Preface
Research Center for ELectron PHoton Science (ELPH), former Laboratory for Nuclear Science(LNS) was established in 1966 attached to Faculty of Science, Tohoku University. In 1967, a largescale 300MeV electron linac was completed, and the 300MeV linac commenced to provide the beams to
not only nuclear physics but many scientific fields. In addition to the higher beam energy, the 300MeV
linac had been operated at a tremendous repetition rate such as 300pps, which is still marvelous forthe current linac technology trend. The 300MeV linac played an important role in a new era of nuclear
physics driven by high-energy electron beam electron beam, and left a number of significant results suchas a study of giant resonance in deformed nuclei via electron inelastic scattering. Furthermore a pulsedneutron from a dense target irradiated by the high-power electron beam was developed for solid-statephysics and other related science, which was conducted by the first director of the Laboratory, Dr. Motoharu Kimura. This historical 300MeV linac is no longer here (the actual maximum energy was ∼220MeV
due to deterioration of accelerating structure shunt impedance in its closing years). Major components of
the 300MeV suffered serious damages due to the Great East Japan Earthquake on March 11, 2011. Since
there was no technical support for the 44-year-old linac, recovering whole function was impossible any
longer. Nowadays superconducting technology has been developed for high average power electron beam,
so that the high-repetition normal conducting linac seems to be left behind. This means it may take ahuge budget to re-construct a 300Hz - 300MeV linac. It was very difficult task to recover the functionsof 300MeV linac. Consequently we have decided to separate major functions of the linac, i.e. production of radioisotopes and beam injection into a 1.2GeV booster synchrotron. Among five 25MW-klystron
modulators, two adequate modulators were recovered as main power sources for a 300Hz - 60MeV linac.
Other usable components and devices in the old linac have been stocked for possible malfunctions in thenear future. A beam transport line into the 1st experimental room where there is a target station for
the radioisotope production was also improved by introducing a new dispersive section and a dispersionfree beam line. The memorial linac was revived as an extremely high beam power linac dedicated to
the radioisotope production. Accordingly handling of the high-power beam has been greatly improved,
so that the stable beam can be provided to users in a short tuning time. Meanwhile, a 1.2GeV booster
synchrotron, the so-called STB-ring, was also recovered and reincarnated as a 1.3GeV booster-storage
ring (BST-ring) by introducing high-performance synchrotron tracking power supplies. Furthermore the
BST ring is now able to store the high beam current more than 100mA theoretically because of replacing
quadrupole magnets with sextupole-quadrupole combined magnets to cure the head-tail instability. A
90MeV injector linac was newly constructed in which an originally developed thermionic RF gun was
introduced for reducing the linac cost. The role of old 300MeV linac is then distributed to the high-power
linac and the injector linac so that parallel operation of two linacs is indeed possible. Detail of recoveringfrom the disaster was reported in an issue “ELPH annual report 2011-2013”.
In 2014, reform of the research building was completed. This might be very much surprising forones who know it used to be. The building looks fine and equips a new conference hall whose seating
capacity is more than 100 people. In addition, utilities in the facility, such as electricity receiving andtransforming station, monitoring system for radiation safety, reservoir pool for polluted water and etc.,
were fixed and mostly improved. In addition to these facts, the alteration of the 300MeV linac, a symbolin the long history of ELPH and LNS, implies an opening of new era of the Laboratory.
Four years have already passed since the big earthquake and tsunami attacked. The scars leftby the tsunami were still visible in every quarter. We should not forget contribution for the local area
alongside of recovering our research activity. In 2014, we have embarrassed particularly by the steep riseof electricity price. However we are going to reverse the situation and let us be substantial parts of thenext generation of the Laboratory. We sincerely ask facility users and related scientific field communities
for strong supports and cooperation.

Director
Hiroyuki Hama

ELPH annual report, 2014
Contents
I. Papers
Current status of meson photoproduction experiments with FOREST
T. Ishikawa, Q. He, Y. Honda, M. Miyabe, N. Muramatsu, H. Shimizu,
Y. Tsuchikawa, H. Yamazaki

1

K0 Λ photoproduction studied with FOREST
Y. Tsuchikawa, R. Hashimoto, Q. He, T. Ishikawa, S. Masumoto, M. Miyabe,
N. Muramatsu, H. Shimizu, Y. Tajima, H. Yamazaki, R. Yamazaki, for the FOREST
collaboration

15

A method to measure the size of hadrons
H. Shimizu, Q. He, Y. Honda, T. Ishikawa, S. Kido, M. Miyabe, Y. Matsumura,
N. Muramatsu, A. Tokiyasu, Y. Tsuchikawa

22

Performance Test of Thin Gap MWPC for In-beam Charged Particle Veto in KOTO
Experiment
27
H. Nanjo, I. Kamiji, K. Nakagiri, M. Sasaki, N. Sasao, M. Sei, Y. Seki, S. Shinohara,
Y. Tajima, H. Yoshida
Development of new detector systems for J-PARC E07
S. H. Hwang, J. K. Ahn, B. Bassalleck, H. Ekawa, Y. Han, S. Hasegawa,
S. Hayakawa, T. Hayakawa, K. Hosomi, K. Imai, M.H. Kim, S.H. Kim, R. Kiuchi,
J. Y. Lee, T. J. Moon, K. Oue, H. Sako, S. Sato, H. Sugimura, K. Tanida, T. Watabe

36

200 MeV/c 陽電子ビームを用いたシリコンストリップセンサーおよび読み出し回路試
作機の性能評価
Evaluation of Test Silicon Strip Sensors and Readout ASICs with the 200 MeV/c
Positron Beam
45
S. Nishimura, H. Ikeda, M. Ikeno, K. Ueno, T. Uchida, K. Kawagoe, S. Koura,
T. Kohriki, N. Saito, O. Sasaki, S. Shirabe, M. Tanaka, J. Tojo, T. Nagasawa,
T. Mibe, T. Yoshioka, for the J-PARC muon g-2/EDM collaboration
Performance evaluation of the readout electro circuit for the PWO counters in the J-PARC
E13 experiment
54
M. Nakagawa, N. Ichige, T. Koike, Y. Sasaki, H. Tamura, M. Ukai, T. O. Yamamoto,Y. Yamamoto
Development of drift chamber for the J-PARC E21 COMET experiment
H. Sakamoto, C. Wu, T. S. Wong, H. Yoshida, Y. Nakazawa, H. Katayama,
T. Yamane, T. Ueda, D. Tsunemori, N. Yokoyama, H. Yong, A. Sato, Y. Kuno,
J. Sato, Z. Zhang, R. P. Litchfield, P. Dauncey

62

Development of a photon tagger with counters based on MPPCs
H. Kanda, T. Fujii, Y. Fujii, M. Fujita, H. Homma, K. Honda, T. Ishikawa,

79

M. Kaneta, Y. Kasai, C. Kimura, J. Kusaka, K. Maeda, S. Nagao, S. N. Nakamura,
A. Ninomiya, T. Nishizawa, K. Nochi, K. Ozeki, T. Sasaki, H. Shimizu,
Y. Takahashi, K. Tsukada, R. Yagi, F. Yamamoto, H. Yamazaki
Test experiment of a prototype RICH counter for the J-PARC E50 experiment
T. Yamaga, R. Honda, T. Ishikawa, K. Kato, M. Naruki, H. Noumi, K. Shirotori,
T. Takahashi

83

Study for the charged particle detector using wave length shifting fibers and MPPC89
M. Miyabe, T. Abe, Y. Inoue, M. Sasagawa, Y. Honda, T. Ishikawa, S. Kido, T. Suda,
Y. Tajima, A.O. Tokiyasu
The performance study of an electro-magnetic calorimeter BGOegg
Y. Matsumura, T. Ishikawa, M. Miyabe, N. Muramatsu, H. Shimizu, H. Hamano,
T. Hashimoto, S. Kido, S. Masumoto, K. Mizutani, K. Ozawa, T. Shibukawa,
K. Shiraishi, A. Tokiyasu, N. Tomida, N. Tran, Y. Tsuchikawa, H. Yamazaki,
R. Yamazaki, M. Yosoi

95

Development of the liquid hydrogen target system for the electromagnetic calorimeter
BGOegg106
N. Muramatsu, T. Ohta, M. Yosoi, Y. Ohashi, W.C. Chang, J.Y. Chen, S. Date,
H. Goto, H. Hamano, T. Hashimoto, Q. H. He, K. Hicks, T. Hiraiwa, Y. Honda,
T. Hotta, H. Ikuno, T. Ishikawa, I. Jaegle, Y. Kasamatsu, S. Kido, Y. Kon,
S. Masumoto, Y. Matsumura, M. Miyabe, K. Mizutani, T. Nakano, M. Niiyama,
Y. Nozawa, H. Ohkuma, H. Ohnishi, M. Oka, K. Ozawa, T. Shibukawa, H. Shimizu,
K. Shiraishi, Y. Sugaya, S. Suzuki, S. Tanaka, A. Tokiyasu, N. Tomida, N. Tran,
Y. Tsuchikawa, H. Yamazaki, R. Yamazaki, T. Yorita
Development of a charge-to-time (QTC) discriminator
T. Ishikawa

113

Commissioning of the Electron spectrometer for the SCRIT electron scattering facility
K. Tsukada, A. Enokizono, K. Kurita, S. Matsuo, Y. Moriya, T. Ohnishi, T. Suda,
T. Tamae, M. Togasaki, T. Tsuru, R. Toba, K. Yamada, S. Yoneyama, M. Wakasugi

125Radiochemical Determination of Photonuclear Reaction Yields for Photon Activation
AnalysisY. Oura, Y. Yamaguchi, Y. Tanaka

132

Study on Metallofullerene Encapsulating Artificial Radio Element of Promethium
K. Akiyama, S. Miyauchi

135

Measurements of thicknesses of Ce targets for (p,γ) reaction
N. Kinoshita, S. Ueno

139

Profile measurement of bremsstrahlung at the irradiation site for RI production
H. Kikunaga for Radioactive-Isotope Science Group144

II. Status Report
Status of accelerator Facilities in FY2014147

Accelerator group
User Support Office Report in FY2014
T. Ishikawa
放射線安全管理室報告
Radiation Safety Report 2014
Radiation Control Office

156

159

III. List of Publication

161

IV. Members of Committees

169

V. Approved Experiments

173

ELPH Annual Report, Tohoku University (2014)

1(ELPH Experiment : #2623, #2640, #2655, #2694)

Current status of meson photoproduction experiments with
FOREST
T. Ishikawa1 , Q. He1 , Y. Honda1 , M. Miyabe1 , N. Muramatsu1 , H. Shimizu1 ,Y. Tsuchikawa1 , and H. Yamazaki1
1Research Center for Electron Photon Science (ELPH), Tohoku University, Sendai 982-0826,
Japan

Meson photoproduction experiments with an electro-magnetic calorimeter FOREST were carriedout from May 2008 to May 2010. The main purpose of the FOREST experiments was to investigate anucleon resonance N ∗ (1670), which is a candidate of anti-decuplet pentaquark baryons, via the γn →
ηn reaction. Ten series of long term FOREST experiments were made before the 2011 Earthquake, andmeasured the differential and total cross sections for the γp → ηp, γd → ηpn, and other reactions.
The photoproduction data were acquired with two STB circulating currents of 1200 and 920 MeV.
The numbers of events collected were 2.13 G, 2.26 G, and 0.24 G events for hydrogen, deuterium, andempty targets in the high energy mode, and those were 211 M, 200 M, and 24 M events in the low energy
one. In this report, the statuses of the analysis on the performance of FOREST from the fiscal year 2014
are presented.

§ 1. Introduction
Quark nuclear physics is a research field where we study the strong interacting matter to understand its properties and interactions coming from underlying fundamental theory Quantum Chromodynamics (QCD). It is a challenge to give an answer to the internal structure of the nucleon and its excitedstates in terms of effective degrees of freedom. Baryon resonance spectroscopy is an important testing
ground for non-perturbative QCD calculations in the low energy scale. Meson photoproduction is utilized for baryon spectroscopy complementary to πN elastic scattering. The γp → π + n and γp → π 0 preactions are intensively investigated at the first stage. Other meson photoproduction processes havebeen investigated in the second stage:
1. multi-meson photoproduction selecting highly excited baryons, and
2. meson photoproduction on the neutron.
A narrow resonance observed in η photoproduction on the neutron is of great interest.
It was observed at Laboratory of Nuclear Science (the former name of ELPH) [6], GRAAL [7], and
CB-ELSA [8]. The resonance would be attributed to a member of anti-decuplet pentaquark baryons
with hidden strangeness since no signature corresponding to this bump has been observed so far in the
proton channel. Fig. 1 shows the baryon octet and anti-decuplet penta-quark baryons. Although theN50 member can be photoproduced from the neutron, photoproduction of the N5+ member having a U-

2spin of 3/2 is forbidden because the U -spin of the proton is 1/2 and that of the photon is 0. The baryon
resonances including this bump has been studied with an electro-magnetic (EM) calorimeter FOREST
at ELPH, Tohoku University by using various photoproduction reactions.

Y=B+S
Θ+
n
Σ−

U3

p
Σ+
1/2

Λ Σ0
Ξ0
1

Ξ−
1/2
Octet
Fig.1.

0

+

Ν5

Ν5

Σ−

Σ0

Q
Σ+
I3

Ξ−− Ξ−
Ξ0
Ξ+
1
1/2
3/2
0
Anti-decuplet

Octet baryons and anti-decuplet penta-quark baryons. The N50 member can be photoproduced from the neutron, but photoproduction of the N5+ member is forbidden due to the
U -spin conservation.

§ 2. Electromagnetic calorimeter FOREST
Meson photoproduction experiments with an electromagnetic calorimeter complex FOREST werecarried out from May 2008 to May 2010 at ELPH, Tohoku University. Bremsstrahlung photons wereused as a beam, being generated with a carbon fiber inserting into circulating 1200 or 920 MeV electrons
in the STretcher booster (STB) ring. Each photon was tagged by detecting the corresponding postbremsstrahlung electron inside a bending magnet of the ring. The details of the photon tagging counter
STB-Tagger II are described elsewhere [9]. The energies of the tagged photon beam ranged from 740 to1150 MeV for circulating 1200 MeV electrons, and from 580 to 880 MeV for 920 MeV ones.
Two γ rays from π 0 → γγ or η → γγ were detected with FOREST. The details of the design of
FOREST are described elsewhere [10] and the status report of FOREST achieved in 2006–2013 can befound in Ref. [11–17]. Fig. 2 shows the schematic view of FOREST.
FOREST consists of different three EM calorimeters: the forward one ‘SCISSORS III,’ the central
one ‘LEPS Backward Gamma detector,’ and the backward one ‘Rafflesia II.’ SCISSORS III is comprisedof 192 pure CsI crystals, LEPS Backward Gamma detector is made up of 252 lead scintillating fiber
modules, and Rafflesia II is composed of 62 lead glass Čerenkov counters. The energy resolution ofeach calorimeter is 3%, 7%, and 5% for 1 GeV photons, which was measured at the positron beamline
for testing detectors at ELPH [18–22]. Plastic scintillator (PS) hodoscopes are placed in front of eachcalorimeter. The forward hodoscopes called ‘SPIDER’ consist of left and right-handed spiral-shaped PS’s,and can determine the incident position of the detected particle. The central and backward hodoscopes
called ‘IVY ’ and ‘LOTUS’ consist of 18 and 12 PS’s, respectively.

3

LEPS Backward Gamma
SCISSORS III

SPIDER

LOTUS
IVY

Rafflesia II

FORESTFig.2.

Schematic view of FOREST. It consists of three EM calorimeters: the forward one with
192 pure CsI crystals ‘SCISSORS III,’ the central one with 252 lead scintillating fiber
modules ‘LEPS Backward Gamma detector,’ and the backward one with 62 lead glassČerenkov counters ‘Rafflesia II.’ The energy resolution of each calorimeter is 3%, 7%,
and 5% for 1 GeV photons. Plastic scintillator hodoscopes are placed in front of thesecalorimeters: SPIDER, IVY, and LOTUS. The photon beam comes from the right side.

Ten series of long term FOREST experiments were made before the 2011 Earthquake, and we callthe periods 2008A–2008C, 2009A–2009E, 2010A, and 2010B. The developed FOREST cryogenic target
system [23] enables us to change targets within 6 hours. The high speed data acquisition system (DAQ)
FOREST-DAQ dedicated to the FOREST experiments [24] was used. The DAQ efficiency was 76% at thetrigger rate of 2 kHz. The details of the FOREST experiments are described elsewhere [15]. The collected
data in the FOREST experiments are summarized in Table 1 in Ref. [16]. Construction of Rafflesia II
finished after the 2008A term ended, and the readout of signals from all the counters in Rafflesia II was
ready from the 2008C. LOTUS was constructed just before the 2009D started. The data taking with thedeuterium target started in the 2008C, and the data for both the hydrogen and deuterium targets wereacquired in a term except for a short term 2009C. The circulating electron energy of the STB ring was
920 MeV for the 2009E and 2010A periods, and 1200 MeV for the other ones.

4§ 3. Progress of the analysis in FY2014
The progress of the analysis in FY2014 is described in this section. The momentum, polar, andazimuthal angle reconstruction for the proton were updated for SPIDER and SCISSORS III [25–27]. The
trigger formation probability especially for SCISSORS III was checked [28, 29]. The energy response to
the proton and photon were investigated in detail [31–33]. The momentum, polar, and azimuthal angle
reconstruction for the photon was also updated for Backward Gamma [30]. The geometry of the Rafflesia
II in the simulation was updated [34, 35]. The knotting process (clustering of the responding plastic
scintillators) was modified [36–38]. The geometries of SCISSORS III and SPIDER including the frameof SCISSORS III were also updated [39–43]. The energy response of SCISSORS III was modified [44],and the target center was also adjusted [45].
3.1 Update of the response of Lead/SciFi modules to the photon
The average number of responding Lead/SciFi modules as a function of photon energy is different
between the experimental and simulation data when a photon injects onto Backward Gamma. The lateral broadening of the EM shower in Lead/SciFi was adjusted in the simulation so that the average
number of responding Lead/SciFi modules in the experimental data were reproduced by the simulation.
Figure 3 shows the photon energy distribution generating one and two blocks together with the probability of generating two blocks as a function of photon energy in response to a photon after the simulation

2000
0

4000
3000
2000
1000
0

Fig.3.

0

200 400 600 800
γ enrgy (MeV)
2010B
n=1

0

200 400 600 800
γ enrgy (MeV)

2009D
n=2

400
200
0

0

600

200 400 600 800
γ enrgy (MeV)
2010B
n=2

400
200
0

0

200 400 600 800
γ enrgy (MeV)=2 PROBABILITY

4000

600

=2 PROBABILITY

6000

Counts / 5 MeV

2009D
n=1

Counts / 5 MeVCounts / 5 MeVCounts / 5 MeV

code has been modified.

1
2009D
0.8
0.6
0.4
0.2
0
0 200 400 600 800
γ enrgy (MeV)
1
2010B
0.8
0.6
0.4
0.2
0
0 200 400 600 800
γ enrgy (MeV)

Photon energy distribution generating one (left) and two (right) blocks, and the probability of generating two blocks as a function of photon energy in response to a photon
after the simulation code has been modified. These are estimated by using the γp → ηpevents. The blue and red histograms show those for the experimental and simulation
results, respectively. The upper and lower panels show the FOREST2009D and 2010B
results.

5

3.2 Check of the trigger formation probability
The trigger logic for the data acquisition system could change more or less the acceptance for the
specified reaction events. Therefore, the trigger formation probability was checked in the various pointsof view: effective threshold of the calorimeter modules and SCISSORS II blocks, and the responding
probability of the blocks. It has been discussed in §3.1 as for the responding probability of the Backward
Gamma blocks.
3.3 Update of the Rafflesia II geometry
The preliminary results for the differential cross sections of the γp → π 0 p reaction differ between
BB and BR, where BB stands for the events that both the two photons are detected with Backward
Gamma, and BR shows the events that they are detected with Backward Gamma and Rafflesia II. Thisdifference is thought to come from the discrepancy of the solid angles of Rafflesia II between the experimental and simulation data. The global z shift of Rafflesia II was adjusted so that the ratio of BR andBB events in the experimental data was reproduced by the simulation for the γp → π 0 p reaction.
3.4 Update of the SPIDER geometry
A discrepancy between the experimental and simulation data exists in the placement of SPIDER
plastic scintillators. The measured polar angles were estimated for the experimental and simulation byusing the γp → ηp events. Figure 4 shows the centroid of the measured polar angle distribution for themost outer overlaps between the first and the second (third) layer of the SPIDER plastic scintillators.
The measured polar angle in the simulation is always larger than that in the experimental data, and

24
23.5
23
22.5
22
21.5
21
20.5
20
19.5
19

Fig.4.

θ (deg) for n13=1

θ (deg) for n12=1

the difference seems constant.

0

100
200
300
Azimuth φ (deg)

24
23.5
23
22.5
22
21.5
21
20.5
20
19.5
19

0

100
200
300
Azimuth φ (deg)Centroid of the measured polar angle distribution for the most outer overlaps between
the first and the second (third) layer of the SPIDER plastic scintillators. The blue andred histograms show those for the experimental and simulation results, respectively. The
vertical bar shows the width (σ) of the measured polar angles.

6

After the modification of the placement of SPIDER plastic scintillators and the global shift of SCISSORS III in z axis, the good agreement between the experimental and simulation data was obtained.
Figure 4 shows the centroid of the measured polar angle distribution for the most outer overlaps between
the first and the second (third) layer of the SPIDER plastic scintillators after the simulation code was

24
23.5
23
22.5
22
21.5
21
20.5
20
19.5
19

Fig.5.

θ (deg) for n13=1

θ (deg) for n12=1

modified. The details of the analysis were described elsewhere [41].

0

100
200
300
Azimuth φ (deg)

24
23.5
23
22.5
22
21.5
21
20.5
20
19.5
19

0

100
200
300
Azimuth φ (deg)Centroid of the measured polar angle distribution for the most outer overlaps between thefirst and the second (third) layer of the SPIDER plastic scintillators after the simulation
code was modified.

3.5 Update of the geometry of SCISSORS III and its frame
A discrepancy between the experimental and simulation data seemed to exist in the proton detection efficiency with SCISSORS III at large polar angles. At first the proton detection efficiency withSCISSORS III was estimated by using the γp → ηp and γp → π 0 p events that two photons are detectedwith Backward Gamma and the proton is detected with SPIDER. The detection efficiency was estimatedthe cluster existing ratio in the selected events. Figure 6 shows the proton detection efficiency as afunction of the momentum for each polar angle that is estimated by using the γp → ηp reaction, andFigure 7 shows that estimated by using the γp → π 0 p reaction. In the γp → ηp reaction, A discrepancy
between the experimental and simulation data appears in the momentum range less than 800 MeV/c inthe polar angle larger than 20◦ . No discrepancy was observed in the γp → π 0 p reaction since no protons
with a momentum less than 800 MeV/c are detected with SPIDER.
The events are classified into four by using the azimuthal angle of the proton detection. The azimuthal angle regions are defined as 1, 2, 3, and 4 for [0, 15◦ ), [15, 45◦ ), [45, 75◦ ), and [75, 90◦ ) in thefirst quadrant, and the regions are defined in the other quadrant by assuming symmetry against the x
and y axes. Figure 8 shows the proton detection efficiency as a function of the kinetic energy for eachpolar angle and each azimuthal angle that is estimated by using the γp → ηp reaction. It seems that
low kinetic energy protons are likely to be blocked by some material.

Efficiency / 20 MeV

7

1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0

0

Fig.6.

250500

4,5 deg

5,6 deg

6,7 deg

7,8 deg

8,9 deg

9,10 deg

10,11 deg

11,12 deg

12,13 deg

13,14 deg

14,15 deg

15,16 deg

16,17 deg

17,18 deg

18,19 deg

19,20 deg

20,21 deg

21,22 deg

22,23 deg

23,24 deg

24,25 deg

750

1000 0250 500 750 1000 0
Proton Momentum (MeV/c)

250

500

750

1000

Proton detection efficiency as a function of the momentum for each polar angle beforechanging the geometry of the SCISSORS III frame, which is estimated by using the γp →
ηp reaction. The blue and red histograms show those for the experimental and simulation
results, respectively. The polar angle is described in each panel. A discrepancy between
the experimental and simulation data appears in the polar angle larger than 20◦ .

Efficiency / 20 MeV

8

1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0

21,22 deg

22,23 deg
0

250 500 750 1000 12500

23,24 deg
250 500 750 1000 1250

24,25 deg
0

250 500 750 1000 1250
Proton Momentum (MeV/c)

Fig.7.

Proton detection efficiency as a function of the momentum for each polar angle beforechanging the geometry of the SCISSORS III frame, which is estimated by using theγp → π 0 p reaction. The blue and red histograms show those for the experimental andsimulation results, respectively. The polar angle is described in each panel. A discrepancy between the experimental and simulation data appears in the polar angle larger
than 20◦ .

The implementation of the SCISSORS III frame made of the iron in the simulation was not realistic
so far. This came from the unrealistic placement of the INS CsI crystals (most outer crystals in SCISSORS III). Therefore, the placement of all the CsI crystals was adjusted by changing the coordinates alittle bit, and the geometry of the iron frame was changed to be realistic. Figure 9 shows the SCISSORS
III frame. No overlap between the iron frame and SCISSORS III crystals was found.
The proton detection efficiency for the simulation data was re-estimated by using the modified codewith a new geometries. Figure 10 shows the proton detection efficiency as a function of the momentum
for each polar angle and each azimuthal angle after changing the geometry of the SCISSORS III framethat is estimated by using the γp → ηp reaction. The discrepancy between the experimental and simulation data disappears. The z coordinate of SCISSORS III was also adjusted again so that the positionof the proton determined by SCISSORS III and that determined by the overlap of SPIDER scintillators
agreed. The details of the analysis were described elsewhere [26, 27].
3.6 Modification of the knotting process
We call a cluster of the responding plastic scintillators in hodoscopes as a knot The knotting process
is modified to incorporate the following together with bug fixes:
1. a charged particle penetrate both the IVY plastic scintillator and CsI crystal,
2. a charged particle penetrate both the IVY and SPIDER plastic scintillators, and
3. a charged particle only penetrate a plastic scintillator in SPIDER (the largest polar angle).
The details of the consideration were found elsewhere [36–38].

Efficiency / 20 MeV

9

Fig.8.

1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0

0

100

200

φ: 1
19,20 deg

φ: 1
20,21 deg

φ: 121,22 deg

φ: 1
22,23 deg

φ: 1
23,24 deg

φ: 124,25 deg

φ: 2
19,20 deg

φ: 220,21 deg

φ: 221,22 deg

φ: 222,23 deg

φ: 223,24 deg

φ: 224,25 deg

φ: 3
19,20 deg

φ: 320,21 deg

φ: 321,22 deg

φ: 322,23 deg

φ: 323,24 deg

φ: 324,25 deg

φ: 4
19,20 deg

φ: 420,21 deg

φ: 421,22 deg

φ: 422,23 deg

φ: 423,24 deg

φ: 424,25 deg

300

400 0

100 200 300 400 0
Proton Kinetic Energy (MeV)

100

200

300

400

Proton detection efficiency as a function of the momentum for each polar angle and eachazimuthal angle before changing the geometry of the SCISSORS III frame, which is estimated by using the γp → ηp reaction. The blue and red histograms show those for theexperimental and simulation results, respectively. The polar angle is described in eachpanel. The discrepancy between the experimental and simulation data appears in thepolar angle larger than 20◦ .

10

Fig.9.

SCISSORS III frame. No overlap between the iron frame and SCISSORS III crystals isfound.

3.7 Update of the determination of the proton kinematic variables
The determination of the proton kinematic variables (momentum, polar, and azimuthal angles)
was updated for SPIDER and SCISSORS III [25–27]. The difference of the parameters between theexperimental and simulation data became smaller.
3.8 Update of the energy response of CsI crystals to the proton
The measured energy distribution for each proton kinetic energy is different between the experimental and simulation data, which causes a wrong estimation of the proton detection efficiency inthe experimental data. Therefore, the light output determination from the energy deposit was modified so that the measured energy distribution in the simulation reproduced that for the experimental
data. Figure 11 shows the measured energy distribution for each 20 MeV kinetic energy bin in responseto the proton after the simulation code has been modified. The measured energy distributions in theexperimental data are well reproduced by the simulation The details of the consideration were foundelsewhere [44].

§ 4. Summary
Ten series of meson photoproduction experiments with FOREST was carried out in 2008–2010. The
main purpose of the FOREST experiments is to study a nucleon resonance N ∗ (1670), which is a candidate of antidecuplet pentaquark baryons via η photoproduction on the neutron. The energy and timing
calibrations of all the detectors have been finished. The software alignment of SPIDER, SCISSORS III,and Rafflesia II has been adjusted again. The estimation of the nucleon detection efficiency has been
completed. The precise determination of the time of flight for the nucleon has also been updated. Now,

Efficiency / 20 MeV

11

1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0

Fig.10.

0

100

200

φ: 1
19,20 deg

φ: 1
20,21 deg

φ: 121,22 deg

φ: 1
22,23 deg

φ: 1
23,24 deg

φ: 124,25 deg

φ: 2
19,20 deg

φ: 220,21 deg

φ: 221,22 deg

φ: 222,23 deg

φ: 223,24 deg

φ: 224,25 deg

φ: 3
19,20 deg

φ: 320,21 deg

φ: 321,22 deg

φ: 322,23 deg

φ: 323,24 deg

φ: 324,25 deg

φ: 4
19,20 deg

φ: 420,21 deg

φ: 421,22 deg

φ: 422,23 deg

φ: 423,24 deg

φ: 424,25 deg

300

400 0

100 200 300 400 0
Proton Kinetic Energy (MeV)

100

200

300

400

Proton detection efficiency as a function of the momentum for each polar angle andeach azimuthal angle after changing the geometry of the SCISSORS III frame, which isestimated by using the γp → ηp reaction. The blue and red histograms show those forthe experimental and simulation results, respectively. The polar angle is described ineach panel. The discrepancy between the experimental and simulation data disappears.

12

600
400
200
0

60,80 MeV
sim x 8.634

200
0

200

400

1000
0

2000

200

400

Counts / 5 MeV

750
500
250
0
150
100
50
0
750
500
250
0
750
500
250
0
750
500
250
0

0

200

400

300,320 MeV
sim x 1.411

0

200

400

380,400 MeV
sim x 1.058

2000
1000
0

0

1000
500
0
600
400
200
0

0

200

400

0

460,480 MeV
sim x 2.541

0

200

400

540,560 MeV
sim x 2.427

0

200

400

620,640 MeV
sim x 2.241

0

200

400

700,720 MeV
sim x 0.976

200

750
500
250
0
750
500
250
0
750
500
250
0

400

200

400

200

400

0

400

0

200

1000
500
0

400

200

400

200

0

200

400

340,360 MeV
sim x 0.984

0

600
400
200
0
200 400
0
480,500 MeV 1000
sim x 2.656

200

400

420,440 MeV
sim x 2.577

200

400

500,520 MeV
sim x 2.644

500
0

0
0
560,580 MeV 1000

200

400

sim x 2.481

200

400

580,600 MeV
sim x 2.432

500
0

200

0

400

640,660 MeV
sim x 2.189

0

200

400

720,740 MeV
sim x 0.544

0

200

400

750
500
250
0
75
50
25
0

200

400

200,220 MeV
sim x 2.451

0

200

400

280,300 MeV
sim x 1.686

500

400

0

400

0

0

260,280 MeV
sim x 1.937 1000

400,420 MeV
sim x 2.042

0

0

1000

200

200

0

0

1000
0

200

120,140 MeV
sim x 1.120500

180,200 MeV
sim x 2.744 2000

100
0100,120 MeV 1000
sim x 0.644

160,180 MeV 3000
sim x 2.609 2000

320,340 MeV
sim x 1.175

400
0

200

600
400
200
0

240,260 MeV 1500
sim x 1.898

200

400

0

0

220,240 MeV 1500
sim x 2.186

1000
0

0

140,160 MeV 3000
sim x 1.849

2000

0

80,100 MeV
sim x 0.604

400

0

200

400

660,680 MeV
sim x 1.915

0

200

400

740,760 MeV
sim x 0.242

0
300
200
100
0
750
500
250
0
750
500
250
0
750
500
250
0

0

400

360,380 MeV
sim x 0.836

0

200

400

440,460 MeV
sim x 2.547

0

200

400

520,540 MeV
sim x 2.614

0

200

400

600,620 MeV
sim x 2.294

0

200

400

680,700 MeV
sim x 1.430

400
200
0

200

0

200

400

760,780 MeV
sim x 0.074

20
10

0

200

400

0

0

200

400

Es (MeV)Fig.11.

Measured energy distribution for each 20 MeV kinetic energy bin in response to theproton after the simulation code has been modified. The blue and red histograms show
those for the experimental and simulation results, respectively.

13

we are working on the slight difference between the experimental and simulation data to finalize the
FOREST data.

Acknowledgment
This work was supported in part by Grants-in-Aid for Scientific Research (B) (17340063), for Specially promoted Research (19002003), for Scientific Research (A) (24244022), and for Scientific Research(C) (26400287).

References[1]

S. Capstick and N. Isgur: Phys. Rev. D 34, 2809 (1986);
S. Capstick and W. Roberts: Phys. Rev. D 47, 1994 (1993);
S. Capstick and W. Roberts: Phys. Rev. D 58, 074011 (1998);
S. Capstick and W. Roberts: Prog. Part. Phys. 45, S241 (2000);
K. Nakamura et al. (Particle Data Group): J. Phys. G 37, 075021 (2010).

[2]

D. Jido, E. Oset, A. Ramos, and U.G. Meißner, Nucl. Phys. A 725, 181 (2003).

[3]

B.S. Zou, Nucl. Phys. A 790, 110c (2007).

[4]

T. Nakano et al., Phys. Rev. C 79, 025210 (2009), and references therein.

[5]

M. Kaliner and H.J. Lipkin, Phys. Lett. B 575, 249 (2003);
R.L. Jaffe and F. Wilczek, Phys. Rev. Lett. 91, 232003 (2003).

[6]

F. Miyahara et al.: Prog. Theor. Phys. Suppl. 168, 90-96 (2007); H. Shimizu: talk at NSTAR2007.

[7]

V. Kuznetsov et al.: Phys. Lett. B 647, 23 (2007).

[8]

I. Jaegle et al.: Phys. Rev. Lett. 100, 252002 (2008).

[9]

T. Ishikawa et al.: Nucl. Instr. and Meth. A 622, 1 (2010).

[10] T. Ishikawa: Internal GeV-γ Analysis Note No. 130A (2009).
[11] T. Ishikawa et al., Research Report of LNS 39, Tohoku University, 35 (2007).
[12] T. Ishikawa et al., Research Report of LNS 40, Tohoku University, 23 (2008).
[13] T. Ishikawa et al., Research Report of LNS 40, Tohoku University, 19 (2008).
[14] T. Ishikawa et al., Research Report of LNS 41, Tohoku University, 7 (2009).
[15] T. Ishikawa et al.: Research Report of LNS 42&43, Tohoku University, 1 (2011).
[16] T. Ishikawa et al.: ELPH Annual Report 1, Tohoku University, 1 (2012).
[17] T. Ishikawa et al.: ELPH Annual Report 2–4, Tohoku University, 43 (2014).
[18] A. Nakamura, T. Ishikawa et al.: Research Report of LNS 42&43, Tohoku University, 75 (2011).
[19] H. Sugai, T. Ishikawa et al.: Research Report of LNS 42&43, Tohoku University, 88 (2011).
[20] K. Mochizuki, T. Ishikawa et al.: Research Report of LNS 40, Tohoku University, 15 (2008).
[21] M. Sato, T. Ishikawa et al.: Research Report of LNS 41, Tohoku University, 22 (2009).
[22] T. Ishikawa et al.: Research Report of LNS 42&43, Tohoku University, 82 (2011).
[23] R. Hashimoto et al.: Research Report of LNS 41, Tohoku University, 31 (2009).

14[24] H. Fujimura et al.: Research Report of LNS 41, Tohoku University, 26 (2009).
[25] T. Ishikawa: Internal GeV-γ Analysis Note No. 353F (2014).
[26] T. Ishikawa: Internal GeV-γ Analysis Note No. 363F (2014).
[27] T. Ishikawa: Internal GeV-γ Analysis Note No. 364F (2014).
[28] T. Ishikawa: Internal GeV-γ Analysis Note No. 354F (2014).
[29] T. Ishikawa: Internal GeV-γ Analysis Note No. 355F (2014).
[30] T. Ishikawa: Internal GeV-γ Analysis Note No. 365F (2014).
[31] T. Ishikawa: Internal GeV-γ Analysis Note No. 357F (2014).
[32] T. Ishikawa: Internal GeV-γ Analysis Note No. 358F (2014).
[33] Y. Tsuchikawa and T. Ishikawa: Internal GeV-γ Analysis Note No. 369F (2014).
[34] T. Ishikawa: Internal GeV-γ Analysis Note No. 360F (2014).
[35] T. Ishikawa: Internal GeV-γ Analysis Note No. 362F (2014).
[36] Y. Tsuchikawa and T. Ishikawa: Internal GeV-γ Analysis Note No. 367F (2014).
[37] Y. Tsuchikawa and T. Ishikawa: Internal GeV-γ Analysis Note No. 368F (2014).
[38] Y. Tsuchikawa and T. Ishikawa: Internal GeV-γ Analysis Note No. 370F (2014).
[39] T. Ishikawa: Internal GeV-γ Analysis Note No. 366F (2014).
[40] T. Ishikawa: Internal GeV-γ Analysis Note No. 373F (2015).
[41] T. Ishikawa: Internal GeV-γ Analysis Note No. 374F (2015).
[42] T. Ishikawa: Internal GeV-γ Analysis Note No. 375F (2015).
[43] M. Miyabe and T. Ishikawa: Internal GeV-γ Analysis Note No. 376F (2015).
[44] T. Ishikawa: Internal GeV-γ Analysis Note No. 361F (2014).
[45] T. Ishikawa: Internal GeV-γ Analysis Note No. 372F (2015).

ELPH Annual Report, Tohoku University (2014)15(ELPH Experiment : #2623, #2640, #2655, #2694)

K0Λ photoproduction studied with FOREST
Y. Tsuchikawa1 , R. Hashimoto2 , Q. He1 , T. Ishikawa1 , S. Masumoto3 ,M. Miyabe1 , N. Muramatsu1 , H. Shimizu1 , Y. Tajima2 , H. Yamazaki1 ,R. Yamazaki1 , and the FOREST collaboration
1

Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826, Japan2

Department of Physics, Yamagata University, Yamagata 990-8560, Japan3

Department of Physics, University of Tokyo, Tokyo 113-0033, Japan

The photoproduction reaction γn → K 0 Λ has been studied with a 4 π electromagnetic calorimetercomplex FOREST at Research Center for Electron Photon Science (ELPH), Sendai, Japan. The K 0
signals were clearly observed via its neutral decay mode: KS0 → π 0 π 0 → γγγγ with incident photon
energy ranging from the reaction threshold to 1.15 GeV. We report the current status for the γd → K 0 Λp
photoproduction.

§ 1. Introduction
Baryon resonances have been experimentally studied by means of meson production reactions tounderstand low-energy scale quantum-chromo dynamics. Photoproduction is one of the useful tools
to reveal the properties of excited baryons. Indeed, they have been intensively investigated via π, η,and multi-π photoproduction reactions. The K photoproduction reactions, which particularly include
charged particles such as K + , also have been well-studied nowadays. However, on the other hand,neutral kaon and neutral hyperon photoprodution reactions have not been studied enough, so that experimental studies are required to confirm some theoretical works. Moreover, K 0 Λ photoproduction
may have the sensitivity to the prominent peak structure observed in the γn → ηn cross section. It isnotable that all of the features on the peak reported by LNS [1], ELPH [2], GRAAL [3], CB-ELSA [4],and MAINZ [5, 6] were consistent with each other. Those results show (1) the center value of the peakis at W ∼ 1670 MeV, (2) the width of the peak is about 20 MeV, and (3) the peak was observed onlyin the ηn cross section while no such structure was observed in γp → ηp reaction cross section. Because of its narrow width, it is questionable that the structure is made by a nucleon resonance. Indeed,
many theoretical interpretations have been advocated. For example, there are possibilities of an exotic
baryon [7], intrinsically narrow states [8], a KY threshold effect [9], and an interference effect of known
resonances [10]. The variety of the scenarios indicates more constraints are needed to understand thestructure. The K 0 Λ system has an isospin 1/2 and includes hidden strangeness which is same as the ηnsystem. Hence, confirmation of the prominent structure via the γn → K 0 Λ reaction is meaningful toreveal its mysterious nature.

16§ 2. Experiment
The K 0 Λ photoproduced events were detected with an electromagnetic calorimeter complex FOREST [11]. The incident photon energy Eγ ranges from the K 0 Λ reaction threshold to 1.15 GeV [12].
FOREST consists of three parts of a calorimeter-hodoscope pair. Forward one consists of 192 pure CsI
crystals and 72 plastic scintillators (PSs), central one consists of 252 Lead/Scintillating fiber modules
and 18 PSs, and backward one consists of 62 Lead glass and 12 PSs. In total, FOREST covers over theentire steering angle range seen from the liquid deuterium target [13]. The energy resolutions of thecalorimeters are 3% [14], 7% [15], 5% [16] for 1 GeV positrons [17].

§ 3. Current status of analysis
The γn → K 0 Λ events were identified by detecting four γs, proton p and π − generated from below
decay chains
K 0 → π 0 π 0 → γγγγ and(1)

Λ → pπ − .

(2)We analyzed the data taken with the liquid deuterium target ignoring the nucleon Fermi motion inthis work. The proton inside a deuteron was assumed as a spectator during the K 0 Λ photoproduction
reactions.
Four γs were identified as neutral clusters that were required to be coincident with each otherwithin [−2, 2) ns. Charge of the incident particle was An event timing criterion of the FOREST tF wasthen given as an average timing of those. Event timing window was also set to [-5, +15) ns from tF .
Two charged particles generated by the Λ decay (Eq. (2)) are searched by means of the timing difference
between its timing and tF . No other neutral particles were required in this analysis. Thus, events
which involved fifth neutral cluster or third charged cluster in the event timing window were rejectedfrom the event selection. Figure 1 shows the timing difference distributions between the remaining
particle and event timing criterion tF . Additional particles (e.g. γ, n, π ± , p) are well observed in thetiming difference distribution. In this energy region, Eγ ≤ 1.15 GeV, the proton has lower velocity thanthat of the charged pion when it flies to forward angle because of the γn → K 0 Λ kinematics. Hence,on the charged particle case, if both of those were detected by the forward calorimeter, later one wasregarded as proton and faster one was regarded as π − . Figure 2 shows the energy correlation between
E: measured energy by the forward calorimeter and ∆E: measured energy by the forward hodoscope foreach particle regarded as the proton and π − . It shows that the charged particles were well separated.
Also the reaction kinematics confines the proton emission angle in the laboratory frame up to 30◦ which
is just a boundary between the forward and central calorimeter. Thus, charged particles detected withthe central or backward calorimeter was regarded as charged pions.
Measured energy, polar angle , and azimuthal angle of the four γs were kinematically fitted [18] to17x 10 22250
2000

Neutral cluster

Counts / 0.1 ns

1750
Charged cluster

1500
1250
1000
750
500
250
0

-4

-2

0

2

4

6

8

10 12 14tremaining - tc (ns)Fig.1. Timing difference distributions of remaining particles and event timing criterion tF . The
blue line shows the timing difference for neutral particles and red one shows that for the
charged particles.

10

5000

10

8

4000

8

6

3000

4

2000

2

1000

ESpπ (MeV)

p
ESp
(MeV)

350
300
250

6

200
4

150
100

2

50
0

0

100

200 300
p
ESe
(MeV)

400

500

0

0

0

100

200 300
ESeπ (MeV)

400

500

0

Fig.2. Energy correlation between ESp : measured energy by the forward hodoscope versus ESe :measured energy by the forward calorimeter of the charged particles regarded as proton(left) and charged pion (right).

satisfy below three constraints
M 2 (γ1 , γ2 ) = m2π0 ,(3)M 2 (γ3 , γ4 ) = m2π0 , and

(4)

2
MX
(γ1 , γ2 , γ3 , γ4 , Eγ ) = m2Λ .

(5)

where M (γi , γj ) is the invariant mass of γi and γj , MX is missing mass as a function of the measured
values of γi and incident photon energy Eγ . Momentum of the K 0 was then reconstructed by summationof its grandchild γs.
Accidentally triggered events contaminate to the selected events. Such events were subtracted bymeans of the sideband subtraction method by using timing difference between a photon tagging counter18

x 10 23000

Counts / 0.1 ns

Prompt Region
2000

Accidental
BG Region1000

0 -8 -6 -4 -2 0 2 4
tTc - tF (ns)68

Fig.3. Timing difference distribution of Tagger and FOREST. The prompt region is shaded by
red and the accidental background regions are shaded by blue.

and that of FOREST tF . Figure 3 shows the timing difference between photon tagging counter: Tagger
and FOREST. Figure 4 shows the 4 γ (i.e. π 0 π 0 from here) invariant mass distribution obtained withkinematic fitted momenta. A clear peak around the K 0 mass (497.614 MeV/c2 [19]) is observed withsame width of the one expected from GEANT4 based Monte Carlo (MC) simulation. The K 0 yield wasestimated about 10k by fitting the distribution with linear combination of 4th polynomial and gaussianfunctions.
The number of the K 0 Λ events were counted by subtracting a simulated background distribution
from the π 0 π 0 invariant mass distribution. Detailed studies proceed to reveal the contaminated reactions. This report shows the results on the assumption that the background distribution is originatedby an non-resonant reaction γn → π 0 π 0 π − p. The background distribution in the π 0 π 0 invariant mass
distribution was fitted by a simulated background distribution. Figure 5 shows the invariant mass distributions for different Eγ of each 50 MeV. The background distributions were almost reproduced by thesimulated distributions for γn → π 0 π 0 π − p reaction.
The FOREST acceptance was examined by use of the MC simulation. Figure 6 shows the acceptanceCM
as a function of the kaon emission angle in the γn center-of-mass (CM) frame cos θK
for different photon

beam energy Eγ . It shows that FOREST can detect overall emission angle of K 0 .
Figure 7 shows differential cross sections as a preliminary result. The cross sections show enhancement as the kaon emission angle becomes backward in the higher Eγ region while they approach flatter
distributions at the lower energies. This result supports the experimental remark in the experimental
observation in the previous measurement of the γn → K 0 Λ reaction reported by K. Tsukada et al. [20].
This fact indicates that the u-channel exchange term may play an important role in this reaction.

19

1800

2

Counts / (5 MeV/c )

1600
1400
1200
1000
800
600
400
200
0

250

300

350 400 450 500 550
0 02
π π Invariant Mass (MeV/c )

600

650

700

Fig.4. The π 0 π 0 invariant mass distribution for different Eγ . Red line shows the fitted function.
Blue dotted line shows only the 4th polynomial component and black dotted line shows
only the gaussian function.

100

cosθCM=[-0.8,-0.6)

cosθCM=[-0.6,-0.4)

100

50

50

50
0
200

400

600

0
200

CM

cosθ

400

cosθ

=[0.2,0.4)

cosθCM=[-0.2,0.0)
50

0
200

600

CM

=[0.0,0.2)

cosθCM=[-0.4,-0.2)

100
100

2

Counts / (10 MeV/c )cosθCM=[-1.0,-0.8)

cosθ

400

600

0
200

CM

=[0.4,0.6)

400

cosθ

0
200

600

CM

=[0.6,0.8)

cosθ

400

600

CM

=[0.8,1.0)

40
40

50

50
0
200

400

600

0
200

400

0
200

600

20

20

20
400

600

0
200

400

0
200

600

400

600

π π Invariant Mass (MeV/c )002

Acceptance (%)

CM
Fig.5. The π 0 π 0 invariant masses at Eγ = [950, 1000) MeV for different cos θK
bins. Blue line
shows fitted background distribution made by MC simulation for the γn → π 0 π 0 π − preaction.

2020Eγ=925.0 MeV

1020Eγ=975.0 MeV

10

20
Eγ=1025.0 MeV

10

20
Eγ=1075.0 MeV

10

Eγ=1125.0 MeV
10

0-1 -0.5 0 0.5 1 0-1 -0.5 0 0.5 1 0-1 -0.5 0 0.5 1 0-1 -0.5 0 0.5 1 0-1 -0.5 0 0.5 1
cosθCM
K

CM
Fig.6. FOREST acceptance for the K 0 Λ photoproduction reaction as a function of cos θK
fordifferent energy bins. A mean value of the incident photon energy is written in eachpanel in MeV unit.

Arbitrary Unit20
10
Eγ=925.0 MeV
Eγ=975.0 MeV
Eγ=1025.0 MeV
Eγ=1075.0 MeV
Eγ=1125.0 MeV
8
6
4
2
0
-1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1
cosθCMK

Fig.7. Preliminary result of γn → K 0 Λ differential cross sections as a function of kaon emission
CMfor different photon energy Eγ . A mean value of anangle in the γn CM frame cos θKenergy range of the photon beam is written in each panel in MeV unit. The y axis isscaled to an arbitrary unit.

§ 4. Summary
Meson photoproduction experiments were carried out at ELPH to study baryon resonances. The
γn → K 0 Λ → π 0 π 0 pπ − → γγγγpπ − events were studied with an electromagnetic calorimeter FOREST.
About 10k K 0 Λ events were confirmed in the π 0 π 0 invariant mass distribution. FOREST successfully
detects K 0 at all of the emission angles in the γn CM frame. The γn → K 0 Λ differential cross sections
showed backward enhancement in higher energy region. The preliminary results agree with the previous
experimental remark reported by K. Tsukada et al. [20].

References[1]

F. Miyahara et al., Progress of Theoretical Physics Supplement 168, 90 (2007).

[2]

T. Ishikawa, Talk at HADRON2013.

[3]

V. Kuznetsov et al., Phys. Rev. Lett. B 647, 23 (2007).

[4]

I. Jaegle et al., Phys. Rev. Lett. 100, 252002 (2008).

[5]

I. Jaegle, et al., Eur. Phys. J. A 47, 89 (2011).

[6]

D. Werthmüller et al., Phys. Rev. C 90, 015205 (2014).

[7]

D. Diakonov et al., Z. Phys. A 359, 305 (1997).

[8]

A. Fix et al., Eur. Phys. J. A 32, 311 (2007).

[9]

M. Döring and K. Nakayama, Phys. Lett. B 683, 145 (2010).

[10] V. A. Anisovich et al., Eur. Phys. J. A 49, 67 (2013).
[11] T. Ishikawa, Int. J. Mod. Phys. E 19, 2393 (2010);
K. Suzuki et al., Mod. Phys. Lett. A 24, 978 (2009).
[12] T. Ishikawa et al., Nucl. Instr. and Meth. 622, 1 (2010).
[13] R. Hashimoto et al., Research Report of LNS 41, Tohoku University, 31 (2008).
[14] A. Nakamura, T. Ishikawa et al., Research Report of LNS 42&43, Tohoku University, 75 (2010);
H. Sugai, T. Ishikawa et al., Research Report of LNS 42&43, Tohoku University, 15 (2008).
[15] K. Mochizuki, T. Ishikawa et al., Research Report of LNS 40, Tohoku University, 15 (2008).
[16] T. Ishikawa et al., Research Report of LNS 42&43, Tohoku University, 82 (2011);

21

M. Sato, T. Ishikawa et al., Research Report of LNS 41, Tohoku University, 22 (2009).
[17] T. Ishikawa et al., Research Report of LNS 40, Tohoku University, 6 (2008);
Y. Tsuchikawa, T. Ishikawa et al., ELPH Annual Report 1, 107 (2010).
[18] T. Ishikawa et al., ELPH Annual Report 2–4, Tohoku University, 119 (2011-2013).
[19] K. A. Olive et al. (Particle Data Group), Chin. Phys. C, 38, 090001 (2014).
[20] K. Tsukada et al., Phys. Rev. C 78, 014001 (2008).

22

ELPH Annual Report, Tohoku University (2014)(ELPH Experiment : #2623, #2640, #2655, #2694)

A method to measure the size of hadrons
H. Shimizu1 , Q. He1∗ , Y. Honda1 , T. Ishikawa1 , S. Kido1 , M. Miyabe1 ,Y. Matsumura1 , N. Muramatsu1 , A. Tokiyasu1 , and Y. Tsuchikawa1
1

Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826

A novel method to measure the size of hadrons is discussed. A Measurement of Bose-Einsteincorrelations (BEC) for identical mesons M makes it possible to extract the radius of hadron H decaying
into M X in the γN → M H → M M X reaction. For example, the root mean square radius of ∆(1232)
can be obtained from an experiment measuring π 0 π 0 BEC by utilizing the ∆ sequential decay process
γN → π 0 ∆ → π 0 π 0 X at the π 0 ∆ photoproduction threshold.

§ 1. Introduction
In the study of hadron structure the information on the size of hadrons is of crucial importance.
Hadron radii, however, are not well measured except for those of some stable hadrons such as the proton, the charge form factors of which have been measured precisely by means of electron-proton elastic
scattering to yield the mean square radius of the proton [1]. Spectroscopy of atomic hydrogen gives alsoprecise values of the proton radius [2]. As far as the measurement of the size of a particle is concerned,
usually the size means the extent of the charge distribution inside the particle. Accordingly electromagnetic probes are employed as measuring tools. We are exploring another method to measure the size of
hadrons, utilizing Bose-Einstein correlation (BEC) effects of two identical bosons.
We succeeded in extracting π 0 π 0 BEC parameters from 2π 0 photoproduction data obtained with
the FOREST electromagnetic calorimeter in a baryon resonance region around 1 GeV [3]. This is thefirst observation of ππ BEC effects in such a low energy region where only a few pions are generated,unlike the case of BEC observations at high energies with large multiplicity. Here we have an idea tomeasure the size of the ∆(1232) resonance by applying a π 0 π 0 BEC analysis to π 0 ∆ photoproduction on
the nucleon.

§ 2. Bose-Einstein correlations of two identical bosons
In general, BEC effects may be expressed with two-particle correlation function CBEC (p1 , p2 ) as
CBEC (p1 , p2 ) =PBEC (p1 , p2 ).
P0 (p1 , p2 )(1)

Here PBEC (p1 , p2 ) denotes the probability density of two identical bosons, subject to Bose-Einstein symmetry, emitted from a source to space-time points y1 and y2 with momenta p1 and p2 , respectively. The∗

Present address: Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900,
Sichuan, P.R. China

23

denominator P0 (p1 , p2 ) corresponds to that of two identical bosons in the absence of BEC. The probability
density PBEC (p1 , p2 ) is expressed as
Z
PBEC (p1 , p2 ) = d4 r1 d4 r2 |ψ2 (p1 , p2 )|2 ρ(r1 )ρ(r2 )where ψ2 (p1 , p2 ) is a symmetrized two-particle plane wave function given byi
1 hψ2 (p1 , p2 ) = √ e−ip1 (y1 −r1 ) e−ip2 (y2 −r2 ) + e−ip1 (y1 −r2 ) e−ip2 (y2 −r1 ) ,
2

(2)

(3)

and ρ(r) represents a normalized emitter source distribution. Here r1 , r2 are the space-time points of
two-boson emitted places in the source. We obtaine|ψ2 (p1 , p2 )|2 = 1 +1 −iq(r1 −r2 )1e+ eiq(r1 −r2 ) ,
2
2

(4)

with q = p1 − p2 andZ
PBEC (p1 , p2 ) =

1
1
d4 r1 d4 r2 1 + e−iq(r1 −r2 ) + eiq(r1 −r2 ) ρ(r1 )ρ(r2 )22= 1 + |f (q)|2 ,using the Fourier transform f (q) of ρ(r),Z
f (q) = d4 re−iqr ρ(r).

(5)

(6)

If the two particles are detected independently,Z
P0 (p1 , p2 ) = d4 r1 d4 r2 |ψ0 (p1 , p2 )|2 ρ(r1 )ρ(r2 )
Z
h
i
1
=
d4 r1 d4 r2 |e−ip1 (y1 −r1 ) e−ip2 (y2 −r2 ) |2 + |e−ip1 (y1 −r2 ) e−ip2 (y2 −r1 ) |2 ρ(r1 )ρ(r2 )2
Z= d4 r1 d4 r2 ρ(r1 )ρ(r2 )
= 1,

(7)

which corresponds to the two-particle probability density without BEC. Therefore the two-particle correlation function can be written by
CBEC (p1 , p2 ) = 1 + |f (q)|2 .

(8)

It should be noted here that the BEC does not mean the correlation caused by the direct interaction
between the bosons, but the correlation just due to the Bose-Einstein statistics.
If a Gaussian type distribution is employed, ρ(r) can be expressed with a function of the worldinterval r 2 from the origin of the source,−(~r 2 − t2 )1,exp
ρ(r) = √2α2( 2πα)4(9)

with
r 2 = t2 − ~r2 .
The Fourier transform of ρ(r1 ) is then written by
 2 2

Z
α q0
α2 q
~2
f (q) = d4 r1 e−iqr1 ρ(r1 ) = −i exp
−
,
2
2

(10)

(11)

24
by means of the Wick rotation in the complex t plane (it = t0 ) and that of ρ(r2 ) likewise. Therefore we
have
Z


2 2
d4 r1 d4 r2 e−iq(r1 −r2 ) ρ(r1 )ρ(r2 ) = |f (q)|2 = exp α2 q02 − α2 q
~2 = e−α Q ,

(12)

and
2

2

CBEC (q) = 1 + e−α Q ,(13)where Q2 ≡ −q 2 . Experimentally we assume the two-particle correlation function can be expressed as
2

2

CBEC (q) = 1 + λe−α Q ,(14)since all the events do not come from the process under consideration. Here λ is introduced to describe
chaoticity which measures the strength of the BEC effects.

§ 3. Application for ∆ sequential decay processes
It is very much important to get Lorentz invariant BEC parameters in the measurement of the∆(1232) radius. The parameter α given in the previous section has something to do with a Lorentz
invariant world interval. The size of ∆(1232) can be measured with the π 0 π 0 BEC method applied toπ 0 ∆ photoproduction events under the following two assumptions.
1. ∆ sequential decay dominance
We assume ∆ sequential decay dominance. As a matter of fact, our experimental data show thatthe ∆ sequential decay process is dominated in 2π 0 photoproduction on the nucleon in the vicinityof the π 0 ∆ photoproduction threshold [3],γN → R∗ → π 0 ∆(1232) → π 0 π 0 N,

(15)

where R∗ is an s-channel intermediate state decaying into π 0 ∆.
2. Space-time coordinates
The space-time coordinates are defined so that the center of the ∆ is the origin of the coordinates
when the first π 0 and ∆ appear simultaneously at t = 0, which is measured at the rest frameof the ∆. In this space-time coordinate frame, the first and second π 0 s take place at r1 and r2 ,

π0
π0

r1
r2

Δ
Fig.1.

Space-time coordinates

25
respectively. And the emittersource distribution
ρ1 (r) for the first π 0 is assumed to be given as−~r 2 + t21
exp
(16)
ρ1 (r) = √2α2( 2πα)4and ρ2 (r) of the second π 0 as1−~
r 2 + t2.
(17)
ρ2 (r) = √exp
2β 2( 2πβ)4
Each of the parameters α and β represents an extent of the distribution in terms of space-time
interval r 2 = t2 − ~r2 .
Under these conditions, Eq. (2) becomesZ
PBEC (p1 , p2 ) = d4 r1 d4 r2 |ψ2 (p1 , p2 )|2 ρ1 (r1 )ρ2 (r2 )Z
1 −iq(r1 −r2 )1 iq(r1 −r2 )44= d r1 d r2 1 + e+ e
ρ1 (r1 )ρ2 (r2 )2
2
1
1= 1 + f1 (q)f2∗ (q) + f1∗ (q)f2 (q)
2
2

 2 2

 2 2
β q0
α q0
α2 q
~2
β2 q
~2
−
exp
−
.
= 1 + exp2222
Therefore the correlation function may be written as
α2 + β 2 2
CBEC (q) = 1 + λ exp −
Q ,
2

(18)

(19)

for 2π 0 emission. The parameter (α2 +β 2 )/2 is a Lorentz invariant quantity of the 2π 0 system, where thesecondly emitted π 0 coming from ∆ decay is delayed due to the life time of ∆. This time component canbe eliminated by a three-dimensional measurement of the distance between the 2π 0 in the ∆ rest frame.
We are actually interested in the three-dimensional size of the 2π 0 emitter. The three-dimensional meansquare distance D 2 of 2π 0 can be given as




Z
−~
r12
−~
r22
1
1
2
2
√
(~
r1 − ~
r2 ) exp
D = √
exp
d3~
r1 d3~r22α22β 2( 2πα)4 ( 2πβ)4= 3(α2 + β 2 )(20)

in the ∆ rest frame. Here the ∆ shows up at the same time when the first π 0 appears at t = 0. At thismoment, the first π 0 event happens at r1 = (o, ~r1 ). (The origin of the space-time coordinates is defined at
the center of ∆ at rest.) The second π 0 appears somewhere in the ∆ at the space-time point r2 = (τ, ~r2 ).
If the pion were a point-like object without dimension, D 2 would represent the mean square distance oftwo places in the ∆ under the condition of α ≈ β. And the mean square radius R2 of ∆ can be obtained
from the relation
D 2 = 2R2 .

(21)

We assume
R = R∆ + Rπ ,(22)

where R∆ and Rπ denote the root mean square radii of ∆ and π, respectively.
The π 0 π 0 BEC size parameter obtained so far is (α2 + β 2 )/2 = 0.828 fm2 , which gives some information on the size of 2π 0 emitter source but not exactly on the size of ∆ because the π 0 ∆ event selection

26

is not completed for the moment. Nevertheless the obtained BEC parameter might yield a size close to
the radius of ∆, since the ∆ sequential decay process is dominated in the γN → π 0 π 0 X reaction at 1
GeV. Thus the root mean square radius of ∆ can be obtained asr3(α2 + β 2 )− Rπ = 1.58 fm − 0.64 fm = 0.94 fm,
R∆ =
2

(23)

where we adopt the pion radius Rπ = 0.64 fm. This is just a demonstration for our method to measurethe ∆ radius. A further data-analysis is going on to select π 0 ∆ events, which will provide π 0 π 0 BEC
parameters to extract the ∆ radius properly.

Acknowledgment
This research was supported in part by the Ministry of Education and Science of Japan (Grant No.
19002003), and JSPS KAKENHI (No. 24244022).

References[1]

J.C. Bernauer et al., Phys. Rev. Lett. 105 (2010) 242001; R. Hofstadter and R.W. McAllister, Phys
Rev. 98 (1955) 217; R. Hofstadter, Rev. Mod. Phys. 28 (1956) 214; P. Lehmann et al., Phys Rev. 126(1962) 1183; L. N. Hand et al., Rev. Mod. Phys. 35 (1963) 335; J. J. Murphy et al., Phys. Rev. C9(1974) 2125; X. Zhan et al., Phys. Lett. B705 (2011) 59.

[2]

B. de Beauvoir et al., Phys. Rev. Lett. 78 (1997) 440; C. Schwob et al., Phys. Rev. Lett. 82 (1999)
4960; R. Pohl et al., Nature 466 (2010) 213; A. Antognini et al., Science 339 (2013) 417.

[3]

Q. He et al., ELPH Annual Report (2011, 2012, 2013) 73.

ELPH Annual Report, Tohoku University (2014)27(ELPH Experiment : #2769)

Performance Test of Thin Gap MWPC for In-beam Charged
Particle Veto in KOTO Experiment
H. Nanjo1 , I. Kamiji1 , K. Nakagiri1 , M. Sasaki3 , N. Sasao2 , M. Sei3 , Y. Seki3 ,S. Shinohara1 , Y. Tajima3 , and H. Yoshida312Department of Physics, Kyoto University, Kyoto, 606-8502

Research Core for Extreme Quantum World, Okayama University, Okayama 700-8530
3Department of Physics, Yamagata University, Yamagata 990-8560

We developed and tested a Thin Gap Chamber with the gas mixture of CF4 and n-Pentane. The
efficiency and timing property for the electron beam were measured. The efficiency over 99.9% can beachieved for minimum ionizing particles with the time-jitter of 20 ns. No instability or no significant
gain drop was observed under the high flux of electron up to 30 MHz/cm2 . It can satisfy the requirementof the KOTO experiment. We also developed an amplifier and shaper with three pole-zero cancellation
circuits. It suppressed the 1/t tail of a MWPC signal and shaped it as narrow as 100 ns. It can resolve
multi pulses in the high rate condition of the KOTO experiment.

§ 1. Introduction
We are conducting the KOTO experiment [1] at J-PARC to search for the rare CP-violating decay,
KL → π 0 νν. The branching ratio is predicted to be 3 × 10−11 in the Standard Model (SM) with thetheoretical uncertainty of ∼1% [2]. Such highly suppressed and well predicted process in the SM is
suitable to detect new physics beyond the SM with some deviation from the prediction. There are somephysics models which predict higher branching ratios as large as two orders of magnitude [3, 4]. We aresearching for such new physics down to the sensitivity of the branching ratio O(10−11 ).
The KOTO experiment uses a 30-GeV intense proton beam slowly extracted to the primary target
in the Hadron Experimental Facility of J-PARC. From secondary particles produced at the target, longlived neutral particles such as KL , neutron, and gamma are selected with a 20-m-long KL beamline.
In the beamline, two collimators shape the beam narrowly with a sharp edge within the solid angle of
7.8 µsr at a 16◦ direction with respect to the primary proton beam. A dipole magnet sweeps out charged
particles. A lead absorber reduces gamma flux. Such neutral beam enters the KOTO detector as shownin Fig. 1 from the left to the right. Some KL ’s decay in the decay volume, which is of our interest.
We identifies the decay KL → π 0 νν by detecting two gammas from the π 0 with an electromagnetic
calorimeter, and by ensuring no other visible particle with a hermetic veto system. A charged-particle
veto counter is needed also in the downstream in-beam area for such purpose.
Neutron and gamma in the neutral beam pass through the decay volume and enter the downstream
in-beam counters. The in-beam charged veto counter should work under the high-flux neutron and28

9: <364%1+ ;** =: :*> *> A*> **!B ?@> **!'**!C**!( :<*>

:<D>

:<LM

#
"
!
$%&

EA-F4/%

84./G-H10I%4JH/.II%K

G.16.2454
3216-+73408*+,-./0123%4542!

#'

Fig.1.

(

)

"!

"#

"'

O

N

"( $%&

Cross-sectional view of the KOTO detector.

gamma, the rates of which are 0.6 GHz in 20 × 20 cm2 area respectively. The required efficiency todetect charged particles from a KL decay is 99.5% in order to reduce backgrounds, which come fromKL → π + π − π 0 , for example.
We prepared a 3-mm-thick plastic scintillator for the in-beam charged veto counter, named Beam
Hole Charged Veto (BHCV) in 2013. It suffered from high counting rate from the beam gamma andneutron, which caused the signal acceptance loss due to accidental veto. Since larger acceptance loss
was expected for planned increase of the beam power in the future, we decided to replace it with a thin
MWPC. A gas chamber with thin film cathodes was adopted because such thin material reduces hits
from gamma and neutron. Furthermore, we selected a MWPC with a shorter wire-cathode gap, Thin
Gap Chamber [5, 6]. It enables fast collection of positive ions from the avalanche process of a MWPC,
which reduces space charge effect, and hence suppresses a gain drop of a MWPC in a high-rate condition.

§ 2. Prototype module of Thin Gap Chamber
We constructed a prototype chamber with the following parameters, the wire spacing 1.8 mm, thewire-to-cathode gap 1.4 mm, and the wire diameter 50 µm. The relatively short gap and thicker wire
realized higher electric field in larger volume.
We used the gas mixture of CF4 and n-Pentane (C5 H12 ), the mixing ratio of which was 55 : 45. The
gas CF4 was known as “fast gas” which realized fast electron-drift velocity. It enables fast response (short
time-jitter) of the chamber. The gas n-Pentane acts as a strong quencher, which is the most efficient UV
absorber among the hydrocarbon gas, and helps its stable operation with its high field in large volume.
The gas volume was 50 mm × 50 mm × 2.8 mm, and 13 wires 50-mm long were stretched in thecenter. The tension of the wires was 300 gw in order to stabilize the positions against the electric force
between the wires. The central 11 wires out of 13 wires were grouped, and the signal was read out as asingle channel. The signal from the outer two wires were not read out, because the electric field of theedge wires was different.
The cathode was made of a Kapton film 50-µm thick. The inner surface was coated with graphite,which formed the cathode electrode. The thickness of the graphite layer was 30 µm, and the surface
resistance was 1 kΩ/2. This thin cathode is an essential part to reduce the counting rate from theinteraction of neutral particles in the KOTO experiment. Compared to a metal cathode, the graphite

29

cathode reduces emission of electrons from the cathode due to the photoelectric effect of UV photons
from the avalanche, thus it helps the stable operation. The Kapton film was stretched with the stress
15 MPa in order to keep the flatness against the electric static force between the wires and the cathode.
The maximum difference of the gap was calculated to be less than 100 µm for the 30 × 30 cm2 area whichcorresponds to the design of the actual chamber for the KOTO experiment. The stress was well within
the elastic range of the Kapton to keep the long-term stability. The long-term stability of the Kapton film
was also tested separately and no significant creep was observed with the stress of 30 MPa in 3 months.
Buffer gas volumes were made on the outside of the gas volume to share the same gas flow, whichenables no pressure difference of the gas between the inside and outside of the cathode film. The buffer
gas volume was closed with an aluminized PET films 12-µm thick, which also acts as an electrostatic
shield covering the chamber.
The frame of the gas volume was made of G10 in order to keep electric isolation between the cathodeground and the high voltage applied on the anode wire. The frame of the buffer gas volume was made ofaluminum. A photos for the construction is shown in where wires were soldered on the frame. Figure 2
right shows the final shape.

Fig.2.

Photos of the prototype chamber. Wires were soldered on the frame (left). Construction
was finished (right).

The signal was readout via a high-voltage-blocking capacitor (470 pF) with a custom-made preamplifier and shaper. The circuit diagram is shown in Fig. 3. A fast low-noise FET-input op-amp,

波形整形部

前段増幅部
C1

C3

1pF

1p

R1

C2

R2

R4

C4

1k

C5

Test
R0

1p

47k
U1

750

4.7p
R3
10k

51

2.7k

100p

U2

R5
3.9k

200
U3

4.7k

C6

U4

R9

47

R12
200

47p

47k
R6

1k

R8

INPUT
C0

R15

R11

R7

U5

R13
4.3k

R10
120k

R16
200

4.7p

OutputR14
750

U1-U5:ADA4817

Fig.3.

Circuit diagram of the pre-amplifier and shaper.

30

ADA4817 [7], was used for the core device, the features of which are shown in Table. 1. The first opTable 1. Typical performance of ADA4817 in the ±5 V operation [7].
MHz
Gain-bandwidth product > 410 √Input voltage noise
4 nV/ √Hz
Input current noise
2.5 fA/ Hz
Input offset voltage
0.4 mV
Input bias current
2 pA
1 pA
Input bias offset current
amp part corresponds to a pre-amplifier, which integrate the input current with the time constant of
47 ns. Then the pole-zero cancellation circuit with the second integration op-amp makes the effective
integration time shorter to be 3.5 ns. The output of the chamber signal at this stage is shown in Fig. 4
left, where the long tail due to the so-called 1/t tail of a MWPC signal can be seen. The following three

Fig.4.

The output of the pre-amplifier part (left) and the output of the shaper (right) are shown.

pole-zero cancellation circuits and op-amps act as a shaper to reduce the 1/t tail of a MWPC signal. The
output of the shaper is shown in Fig. 4 right, where the 1/t tail is totally vanished, and the width of the
waveform is shortened to be ∼ 100 ns.

§ 3. Performance test
3.1 Setup of the beam test
An electron beam with the energy of 500 MeV was used for this test. The setup is shown in Fig. 5.
Three defining trigger counter, T1, T2, and T3 were used, which were plastic scintillators 5-mm thickwith the area of 10 × 10 mm2 . A timing counter T4 or T5 was also used, which was a plastic scintillators
10-mm thick with the area of 50 × 70 mm2 . The signal was read out from the both ends to improve thetiming resolution. The trigger was made with the coincidence of all the plastic scintillators. The timing
was determined with the mean time of the both ends for the timing counter, where the timing resolutionof 0.21 ns was obtained from the timing difference of the both ends.
We used the extraction of the electron beam with a 6-second extraction in a 12-second cycle for thetest under a low counting rate. We also used a special extraction of the electron beam for the test under a31

Fig.5.

Set up of the beam test.

high counting rate condition. Here the smoothing of the beam was not applied and the extraction period
was shortened.
3.2 Test under low counting rate
The output charge of the chamber at the high voltage of 2.9 kV was obtained with a CAMAC chargesensitive ADC as shown in Fig. 6. A minimum ionization peak (MIP) can be seen at 56.8 pC. The
efficiency of 99.95% was obtained with the threshold at 6 pC (separation from the pedestal by 3 times
rms of the pedestal). The timing distribution at the high voltage of 2.9 kV was obtained with a CAMAC
TDC as shown in Fig. 7. The “time-jitter” was defined with the time gate which contains 99.99% of theevents excluding over-flow events. The time-jitter of 20 ns was obtained at the high voltage of 2.9 kV.

Fig.6.

The output charge of the chamber at the high voltage of 2.9 kV
measured with a CAMAC chargesensitive ADC.

Fig.7.

The timing distribution of thechamber at the high voltage of 2.9
kV obtained with a CAMAC TDC.

The high-voltage dependence of the output charge is shown in Fig. 8, where the charge corresponding to the MIP is used. It shows the saturating behavior compared to the expectation in the proportional

32

mode of a MWPC where an exponential dependence is expected. The operating mode seems to be thelimited proportional mode. Proportionality is not important because this chamber is used for the veto.
The limited proportional mode is rather suitable because it is robust against variation of the MWPC
cell structure, such as wire-to-cathode gap, wire spacing, and so on. The high-voltage dependence of thetime-jitter is shown in Fig. 9. The threshold and the definition are the same as in Fig. 7. It saturates∼ 20 ns at the high voltage 2.9 kV or more.

Fig.9.
Fig.8.

Output charge as a function of thehigh voltage.

Time-jitter as a function of the highvoltage.

The inefficiency (1 − efficiency) was calculated with the same threshold and the time gate as in
the definition of the time jitter. The high-voltage dependence is shown in Fig. 10, where the required
efficiency of 99.5% can be achieved at the high voltage of 2.7kV or more.

Fig.10.

Inefficiency (1 − efficiency) as a function of the high voltage.

33

3.3 Test under high counting rate
The shorter beam spill was used to achieve high-counting rate condition. The electron incident rate
was measured with the trigger counter nearest to the chamber (10-cm downstream of the chamber) withthe area of 10 × 10 mm2 . The discriminated pulse was counted with a CAMAC scaler and the external
clock was also counted with the CAMAC scaler simultaneously. The scaler counts as a function of theactual time for a spill are shown in Fig. 11. The extraction period was ∼ 0.1 s in this condition. The
incident rate of the electron can be obtained with the differentiation of the scaler counts as shown in
Fig. 12. The incident flux also can be obtained with the area of the trigger counter. The rate reached to
120 kHz or the flux reached to 120 kHz/cm2 during the spill.

Fig.11.

Scaler count of the trigger scintillator nearest to the chamber as afunction of the actual time measured with a clock.

Fig.12.

Incident rate of the beam electron.
The vertical axis can be read as anincident flux (kHz/cm2 ) because
the area was 10 × 10 mm2 .

The output charge of the chamber as a function of the incident rate is shown in Fig. 13, where no
significant gain drop is observed. Figure 14 shows the output charge distributions for three incident rate
conditions, less than 10 kHz/cm2 , 10-20 kHz/cm2 , and 20-30 kHz/cm2 . Here no significant difference
was observed. It shows the rate tolerance of the chamber up to 30 kHz/cm2 , which is the expected
maximum hit rate in the unit area for the KOTO experiment in the future.
In this performance test, we also used an ADC with 500-MHz sampling which was used in theactual KOTO experiment. Waveforms captured with the ADC in this high rate test are shown in Fig. 15.
The stability of the base line can be seen and over-wrapped multi pulses in the right figure seems to beresolved. We simulated the high counting rate condition by overlaying the captured pulse. A pulse-fitting
method was developed and the simulated waveforms were fitted. We still achieved 99.9% efficiency withthe threshold of the 1/4-MIP level at the high voltage of 2.9 kV.

§ 4. Summary
The basic performance of the thin gap chamber with the gas mixture of CF4 and n-Pentane wasmeasured at the first time. We developed a chamber with the area of 5 × 5cm2 . The wire spacing was
1.8 mm, the wire-to-cathode gap was 1.4 mm, and the wire diameter was 50 µm. The efficiency over
99.9% can be achieved for minimum ionizing particles with the time-jitter of 20 ns at the high voltage

34

Output charge of chamber as afunction of the incident rate in
10 × 10 mm2 .

Fig.14.

600

amplitude [ADC count]amplitude [ADC count]Fig.13.

550
500
450
400

600
550
500
450
400

350

350

300

300

250

250

200
0

Fig.15.

50

100

150
200
250
sample No. (interval 2ns)

The
distributionsoftheoutput charge for the incident fluxes of less than
10 kHz/cm2 ,10-20 kHz/cm2 ,2
and 20-30 kHz/cm .

200
0

50

100

150
200
250
sample No. (interval 2ns)

The waveforms captured with a ADC with 500-MHz sampling in this test. The ADC wasan actual ADC used in the KOTO experiment.

of 2.7 kV or more. We plan to use three chambers in the KOTO experiment and take two-out-of-threelogic, where the requirement of the efficiency for the single chamber can be lowered to be 90.5%. It isalso robust against occasional sparking or trip of the high voltage, although there was no trip of the highvoltage or observable sparking in this test. We didn’t observed no instability or no significant gain drop
under the high flux of electron up to 30 MHz/cm2 , which is expected to be the maximum counting ratein the unit aria for the KOTO experiment. It guarantees that our chamber will work properly satisfying
the requirement of the efficiency in the environment of the KOTO experiment.
We also developed an amplifier and shaper with three pole-zero cancellation circuits. It suppressed
the 1/t tail of a MWPC signal and shaped it as narrow as 100 ns. We simulated the high rate conditionof the KOTO experiment with overlaying the captured waveforms, and expected no significant increaseof the inefficiency due to the pile up of the waveforms in the condition of the KOTO experiment. It guarantees that our amplifier and shaper will work properly in the environment of the KOTO experiment.
Based on the results, we already developed the actual thin gap chamber with the area of 30×30 cm2

35

for the KOTO experiment. Three chambers were constructed and installed in the KOTO experimental
site, and have worked in the physics run in April 2015. The long-term stability including the aging effectwill be studied in the KOTO beam.

Acknowledgment
We would like to express our gratitude to staffs of the Research Center for Electron Photon Science.
Part of this work was supported by JSPS/MEXT KAKENHI Grant Numbers 23224007 and 25400309.

References[1]

T. Yamanaka [KOTO Collaboration], PTEP 2012, 02B006 (2012).

[2]

A. J. Buras, D. Buttazzo, J. Girrbach-Noe and R. Knegjens, arXiv:1503.02693 [hep-ph].

[3]

M. Blanke, arXiv:1412.1003 [hep-ph].

[4]

M. Blanke, PoS KAON 13, 010 (2013) [arXiv:1305.5671 [hep-ph]].

[5]

S. Majewski, G. Charpak, A. Breskin and G. Mikenberg, Nucl. Instrum. Meth. 217, 265 (1983).

[6]

K. Nagai, Nucl. Instrum. Meth. A 384, 219 (1996).

[7]

Analog Devices, Inc., http://www.analog.com/media/en/technical-documentation/data-sheets/
ADA4817-1_4817-2.pdf

36

ELPH Annual Report, Tohoku University (2014)(ELPH Experiment : #2779)

Development of new detector systems for J-PARC E07
S.H. Hwang1 , J.K. Ahn2 , B. Bassalleck3 , H. Ekawa1,4 , Y. Han1 , S. Hasegawa1 ,S. Hayakawa1,5 , T. Hayakawa5 , K. Hosomi1 , K. Imai1 , M.H. Kim2 , S.H. Kim2 ,R. Kiuchi6 , J.Y. Lee7 , T.J. Moon7 , K. Oue5 , H. Sako1 , S. Sato1 , H. Sugimura1 ,K. Tanida1 , and T. Watabe8
1Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195,
Japan
2
3

Department of Physics, Korea University, Seoul 136-713, Republic of Korea

Department of Physics and Astronomy, University of New Maxico, NM 87131, USA
4
5

6

Department of Physics, Kyoto University, Kyoto 606-8502, Japan

Department of Physics, Osaka University, Toyonaka 567-0047, Japan

Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan

7

Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Republic of
Korea
8

Department of Physics, Nagoya University, Nagoya 464-8602, JapanWe are developing a new large acceptance forward spectrometer, KURAMA, for systematic study of
S = -2 system using the hybrid-emulsion method at J-PARC. We have developed new detector system,
which is composed of a single-sided silicon micro-strip detector (SSD), a beam-hodoscope (BH), a beamaerogel-Cherenkov=counter (BAC), a proton-veto-aerogel-Cherenkov-counter (PVAC) and a charge-hodoscope(CH). A test experiment was performed to evaluate performance of new detector systems with 500 MeV/cpositron beams at the ELPH facility, Tohoku University in June 2014.

§ 1. Introduction
Double strangeness (S = -2) systems have gained considerable attention over the past decades, because of their important role to understand baryon-baryon (B-B) interaction in SU (3) flavor. Also it
plays a key role in the understanding of the multi-strangeness matter, such as the core of the neutronstars. For hyperon (Y ) - nucleon (N ) interaction (S = -1), where hyperon consists of three quarks including at least one strange quark, only 35 species of Λ-hypernuclei are known. However, for Y -Y (S= -2) interaction, only a few double-Λ hypernuclei have been reported. Among them, only one double-Λ
hypernuclei event, called N AGARA event, was clearly identified as the decay of 6ΛΛ He hypernuclei inthe hybrid emulsion experiment [1]. The two-Λ binding energy (BΛΛ ) and the Λ-Λ interaction energy(∆BΛΛ ) were measured to be 6.91 ± 0.16 and 0.67 ± 0.17 MeV, respectively [2]. More samples are still
desired to extend the understanding of Λ-Λ interaction in the nuclei. J-PARC proposed experiment E07
is systematic study of S = -2 systems by the hybrid-emulsion method and it is expected to obtain about

37

Fig.1.

A picture of the test module of SSD.

100 double-hypernuclei candidates [3].
A new magnetic spectrometer, KURAMA, is developed to identify outgoing K + in the C(K − , K + )Ξ− X
reaction at forward angles. Originally the KURAMA spectrometer was used for the experiments at the
KEK-PS beamline. For the new experiment, E07, a pole gap of the KURAMA dipole magnet was increased from 50 cm to 80 cm to get a maximum acceptance at the forward scattered angles. To meetrequired acceptance, new detector systems were fabricated , which are a single-sided silicon micro-strip
detector (SSD), a beam-hodoscope (BH), a beam-aerogel-counter (BAC), a proton-veto-aerogel-counter(PVAC) and a charge-hodoscope (CH). We performed a test experiment for new detector systems with
500 MeV/c positrons at the GeV gamma beamline at the ELPH facility, Tohoku University.

§ 2. New detector systems
This section deals with the new detector systems for the new KURAMA spectrometer.
2.1 A single-sided silicon micro-strip detector (SSD)
The hypernuclei can be found by themselves in the emulsion experiments, but it takes long timeto analysis whole emulsion. Ξ− particles are produced via (K − , K + ) reaction in the diamond target
and stopped in emulsion plates. In the hybrid emulsion method, the incident position of Ξ− in theemulsion plate can be reconstructed with vertex information from SSDs together with information fromother counters and trackers [4]. The silicon sensors are single-sided and a p-in-n type manufactured byHamamatsu Photonics [5]. The sensor has total 1,792 strips with a strip pitch of 50 µm and 320 µm
thick. Among them, 1,536 strips are bonded to 12 APV25 front-end chips and the total effective area is
77[W] × 77[H] mm2 .
One stack consists of 4 layers of sensors in XY X 0 Y 0 order and the APVDAQ VME modules areused to acquire a pulse shape of SSDs. In the test experiment, the SSD module with two layers of SSDs

38(a) BACs

Fig.2.

(b) PVAC

A picture of a beam-aerogel-Cherenkov counters (a) and a proton-veto-aerogel-Cherenkov
counter (b).

with the XY configuration was fabricated to evaluate the operation of new sensors at the ELPH facility
as shown in Figure 1.
2.2 A beam hodoscope (BH)
Time-of-flights (ToF) of charged particles are measured by a Beam-Hodoscope (BH) and a Time-ofFlight wall. A good ToF resolution is guaranteed for reliable particle identification, because the massesof the reconstructed charged particles can be calculated by the relation m2 = p2 (1 − β 2 ), where β =L/(c · ToF). L is the flight length and c is the speed of light in vacuum, respectively. Two type of
the plastic scintillators, Eljen EJ-212 and Eljen EJ-230 [6], were used and the size of scintillator is40[H] × 120[W] × 6[T] mm3 . EJ-212 shows better light yield, while EJ-230 has good timing property.
Fishtail light guides were coupled to the both upper and lower sides of the plastic scintillator. Two 2inch-diameter PMTs, Hamamatsu H10570 and Hamamatsu H2431-50 [5], measures scintillation lightsfrom the scintillator. A Teflon sheet in 200 µm thick or an aluminized Mylar were used for wrapping
scintillators to optimize time resolution of BH’s.
2.3 A beam aerogel counter (BAC)
A beam aerogel counter (BAC) is important to reduce backgrounds, such as pions, muons and electrons, at the online level. Two BACs are used at the online level trigger because knock-on electrons
from K − beams make an over-killing signal about 5 % for one counter. Figure 2 (a) shows the fabricated
BACs. The size of window is 170[W] × 70[H] mm2 and the diffusion box has an inclined plane with
61.3 degree. In side of the diffusion box, four layers of n = 1.03 aerogel radiators were stacked at the
upstream of BAC. Two 3-inch fine-mesh PMTs (Hamamatsu R6683 MOD [5]), which were used for the
belle experiment, were jointed in the bottom of the diffusion box. A single layer of GORETEX is used asreflector for one of the BAC, while a triple-layer Teflon sheet is covered for another BAC.

39

Fig.3.

A photo of a charge hodoscope.

2.4 A proton veto aerogel counter (PVAC)
A high reflective index aerogel is recently developed by Chiba Univ.. The aerogel with high reflective
index is used to identify the scattered K + from the Ξ− production at forward angles. A prototype of PVAC
was fabricated to study a design of diffusion box as shown in Figure 2 (b). The radiator of PVAC is an
aerogel with high reflective index of 1.163 and 113[H] × 113[W] × 13[T] mm3 . The size of the diffusion
box is 120[W] × 120[H] × 70[T] mm3 and four 2.5-inch fine-mesh PMTs are attached to both sides tocollect Cherenkov lights. 300 µm thick Teflon sheet was used at the up and downstream windows. On
the other hand, the side of the diffusion box used 700 µm thick Teflon sheet.
2.5 A charge hodoscope (CH)A charge hodoscope (CH) is used to identify the charge and rough naive momentum of the scattered particle by information of hit segment with both CH and ToF wall in the 1st level trigger (matrix
trigger) and the 2nd level trigger (mass trigger and momentum trigger). The CH consists of 64 plastic scintillators with size of 2 x 11.5 x 450 mm3 as shown in Figure 3. Each segment is overlappedwith adjacent segments by 1 mm. The signal is read out by MPPC (multi-pixel photon counter) withwavelength-shifting-fiber (WLS-fiber). Since it is located inside of the KURAMA dipole magnet, hightolerance against strong magnetic field is needed for CH. The WLS-fiber is inserted in the 1mm-depth
groove in a single side of scintillator. The 1x1 mm2 MPPC with the Kuraray Y11 WLS-fiber [7] collects
scintillation lights at a side. The SPIROC board is used in the read-out electronics and the logic signal
from the SPIROC board is used in the 1st and 2nd level trigger.

§ 3. Test experiment
3.1 Experimental setup
Figure 4 shows an experimental setup at the GeV gamma beamline at the ELPH facility. All detectors were aligned along to the beam line. We prepared two large size of trigger counters, 144[W] × 44[H]× 10[T] mm3 , to estimate intrinsic time resolution, which large trigger counter used two Hamamatsu

40

H1949 PMTs and PMTs are coupled with both edges. In additional, small trigger counters, 9.3[W]× 9.4[H] × 4[T] mm2 and 9.5[W] × 9.8[H] × 4[T] mm2 , used to estimate position dependency. Largecounter and small counter were located most both up and downstream sides to identify positron beams.
Among three SSDs, up and downstream SSDs are reference SSDs, which were used for the J-PARC E10
experiment [8]. A shower veto counter was located downstream of aerogel counters. The size of shower
veto counter is 25 × 25 cm2 and it has φ30 mm hole in the center of the scintillator. The hole was aligned
to the beamline and it was used to suppress the shower events from positron beams.

Fig.4.

Experimental setup for a test experiment.

The trigger rate was 5000 count/spill (16s cycle) and about 1% events were survived by requiring
hits on small counters and no showered events.
3.2 Results
3.2.1 SSD
The efficiency of SSDs are measured by comparing with the reference SSDs and these are estimatedto be 98.7 % and 99.4 % for X-layer and Y-layer, respectively. However, X-layer has 10 dead strips in hit
region, whereas those in Y-layer is 1 strip. It can reflect lower efficiency of X-layer. We found that highrms level of X-layer than that of Y-layer. It came from loose connection of the ground line between APV25
front-end chips and their power lines [4]. The problem has been solved to the final SSD modules. We
successfully estimated the beam profile by hit pattern of new SSDs as shown in Figure 5. Figure 5 (a)shows the beam profile of positron beams. The x and y widths of beam are estimated to be 10.6 mm and5.3 mm, respectively. By requiring no hit on shower veto counter, the beam profile became circle shapedue to the hole shape of shower veto counter as shown in Figure 5 (b). Figure 5 (c) shows the beamprofile by requiring small trigger counters. The shape of small trigger can be seen, but the boundary is
not clear. It is caused by the multiple scattering of the positron beams.
3.2.2 BH
We estimated intrinsic time resolution of BHs depending on different positions and different typeof scintillators. Small beam size was selected by requiring hits on the small trigger counters. The time-

41
Beam Profile with the Finger Counter1&2 Cut

20

350
281073−6.924
0.584
300
10.6
5.261
250

10

bpv
Entries 104402
250
Mean x−3.601
Mean y0.5164
RMS x
6.135
RMS y
4.43

30

20

bpfs
Entries
9240
60
Mean x0.4736
Mean y−1.652
RMS x
2.94
50
RMS y
3.601

30

20

200

10

10

40

150

200
0

Y (mm)

Beam Profile with the Veto Counter Cut
bp
Entries
Mean xMean yRMS x
RMS yY (mm)Y (mm)

Beam Profile without Cut
30

0

0

30

− 10

20

− 20

10

150
100
− 10

− 10
100

− 20

50

− 30
− 30

− 20

− 10

0

10

20

30
X (mm)(a) Beam profile

0

50

− 20

− 30
− 30

− 20

− 10

0

10

20

30
X (mm)

0(b) Beam profile w/o shower veto counterhit

Fig.5.

− 30
− 30

− 20

− 10

0

10

20

30
X (mm)

0(c) Beam profile w/ small trigger hits

Reconstructed beam profiles by new SSD√
walk correction of the large counters was performed with the T DCcor = T DCraw − a/ ADCraw + b
relation, where T DCcor is the corrected T DC, T DCraw is the raw T DC and ADCraw is the raw
ADC. a and b are fitting parameters. Three ToF’s are defined as T oFBHH10571 −T rig2 , T oFBHH2431 −T rig2
and T oFBHH10571 −BHH2431 , where are the time-of-flight between BHH10571 and T rig2 , BHH2431 andT rig2 , BHH10571 and BHH2431 , respectively. The intrinsic time resolutions σBHH10571 , σBHH2431 andσT rig2 can be estimated by the following equations,
2
2
σBH
= σBH
+ σT2 rig2
H10571 −T rig2
H10571
2
2
σBH
= σBH
+ σT2 rig2
H2431 −T rig2
H2431
2
2
2
σBH
= σBH
+ σBH
,
H10571 −BHH2431
H10571
H2431

where σ shows resolution of time-of-flight of each combinations. The estimated intrinsic time resolutions
depending on X-incident position are shown in Figure 6. BH with H10571 PMT (Figure 6 (a)) shows
various intrinsic time resolutions than that of BH with H2431-50 PMT. It is caused by small light yield of
EJ-230 and low gain of H10570 PMT. Reflector with an aluminized Mylar shows better timing properties,
because Teflon is random reflector and the pass length of scintillation has large variation. In the caseof H2431-50 PMT, the intrinsic resolutions show similar distributions for different type of scintillatorsand reflectors. The best timing resolution,however, shows 95 ps. We found that H10570 PMT with EJ230 and an aluminized Mylar shows best intrinsic time resolution about 85 ps and almost no position
dependency in X-position.
3.2.3 BAC
To normalize gain of two PMTs, we estimated single-photo-electron (SPE) channel in the LED test
bench at the laboratory test. The SPE level was measured by the zero probability of the Poisson distribution with weak LED intensity as relating with Pzero = e−λ , where λ is mean photoelectrons. Figure
7 shows the estimated number of photoelectrons for two BACs. Teflon reflector is better light collection
efficiency than that of GORETEX, due to the 10 % better intrinsic reflectance for Teflon sheet. The estimated number of photoelectrons are more than 20 photoelectrons for positron beams. The inefficiency
of BACs are negligible because the inefficiency of BAC from the Poisson distribution is 2.1 × 10− 9.

42

200
150
100
EJ-212, Al Mylar
EJ-230, Al Mylar
EJ-230, Teflon

50
0
-6

-4

-2

0

2

4

6

250
EJ-230, Al Mylar
EJ-212, Al Mylar
EJ-212, w/o reflector

200
150
100
50
0
-6

-4

-2

0

2

4

6

Incident beam position (cm)Incident beam position (cm)(a) H10570 PMT(b) H2431-50 PMT

35

TeflonNPE

Intrinsic resolutions for each condition. (a) shows the measurement with H10571 PMT
and (b) is the measurement with H2431-50 PMT, respectively.

NPE

Fig.6.

H2431-50250

Intrinsic TOF resolution (ps)Intrinsic TOF resolution (ps)H10571

35

30

30

25

25

20

y : +1 cm
y : 0 cm
y : -1 cm-5

GoreTex20
0

5BAC1, x position (cm)(a) BAC1, Teflon

Fig.7.

y : +1 cm
y : 0 cm
y : -1 cm

-5

0

5

BAC2,x position (cm)(b) BAC2, GORETEXDistribution of number of photoelectrons at center position.

3.2.4 PVAC
SPE levels for 4 PMTs were estimated from the LED test bench as similar as the BAC’s normalization method. Positron beams were irradiated for 5 positions at PVAC. Figure 8 (a) shows the reconstructed number of photoelectrons of PVAC, when positron beams inject at center. The estimatedmean photoelectrons are 32.6 photoelectrons at center. The histogram has a large tail at high energy
side compared to the Poisson distributions, but the peak position consistents to a result of Monte-Carlosimulation (20.8 photoelectrons). Other 4 positions were also irradiated as shown in Figure 8 (b). The
estimated photoelectrons are 30.8, 31.7, 32.0 and 32.0 for (2.5 cm, -2.5 cm), (2.5 cm, -2.5 cm), (-2.5 cm,
2.5 cm) and (-2.5 cm, -2.5 cm) positions, respectively.
3.2.5 CHMPPC shows very good photon counting characteristic and our MPPC module can clearly countmore than 10 photoelectrons in the LED test bench. During the test experiment, all channels werenormalized to 30 channel of SPE. Figure 9 shows gain dependency of all 64 channels. All channels showY [mm]

43
33

50
40

32.5

30
20

32

10
31.5

0
! 10

31

! 20
! 30

30.5

! 40
! 50
! 50

! 40

! 30

! 20

! 10

0

10

20

30

40

50
X [mm]

30(a) Histogram of number of photoelectrons (b) Number of photoelectrons depending on the incident beam
at center
positionsFig.8.

Histogram of number of photoelectrons of PVAC at center (a) and the reconstructed number of photoelectrons depending on the beam positions (b).

more than 20 photoelectrons. Normally, MPPC has high dark counting rate, 600 kcps, and it needs a littlehigh threshold level to reduce fake events from dark count. By assuming 4 SPE threshold level, efficiency
can be estimated as 99.998 % in the Poisson distribution. The obtained number of photoelectrons meets
our requirement. Efficiency was estimated in terms of Y-position and incident angle as shown in Figure
10 (a) and (b), respectively. The efficiency of Y-positions show about 99.98 % and it is almost closed toour expectation by the Poisson distribution.
We estimated efficiency depending on the incident angle of positron beams. Particles with large
incident angle can hit corner of scintillators, since each segment is overlapped with adjacent segmentsby 1 mm. In additional, if adjacent segments have a space, the inefficiency will be increased. In the
Figure 10 (b), the inefficiency is less than 0.1 %. The inefficiency is small, however this inefficiency islarger than that of our expectation. Because 1 mm overlapping can cover 20 degree of incident angle.
This large inefficiency is mainly space problem between each segment.

Fig.9.

Distribution of number of photoelectrons at center position.

Efficiency[%]

Efficiency[%]

44

100

99.99

100

99.98

99.98

99.96

99.97

99.94

99.96

99.92

99.95
99.9
99.94
99.88

99.93

99.86

99.92
-20

-15

-10

-5

0

5

10

15

20

0

5

Y position from center[cm](a)方向

Fig.10.

10

(b)
角度

15

20

Angle[degree]

Y-dependency (a) and angular dependency (b).

§ 4. Summary
We carried out a test experiment to evaluate the performance characteristics of SSD, BH, BAC,PVAC and CH for the J-PARC E07 experiment. The beam profile was clearly reconstructed by new
SSD system and we have confirmed an operation of new SSD. The estimated intrinsic time resolutionof BH is reached to 85 ps and it is good enough to identify the scattered K − from the (K − , K + ) reaction. Two aerogel counters,BAC and PVAC, were tested and the obtained gain expects good efficiencyof these detectors. Number of photons of all channel of CH show more than 20 photons. The estimatedcharacteristics of all new detectors meet our requirements to perform the J-PARC E07 experiment.

Acknowledgment
The authors gratefully acknowledge the contributions of the staff at the ELPH facility, Tohoku
University.

References[1]

H. Takahashi et al.: Phys. Rev. Lett. 87 (2001) 212502[2]

J.K. Ahn et al.: Phys. Rev. C 88 (2013) 014003[3]

K. Imai, K. Nakazawa and H. Tamura et al.: J-PARC proposal E07, Systematic Study of double
strangeness system by emulsion-counter hybrid method.

[4]

J.Y. Lee et al.: Proceeding of J-PARC 2nd symposium., in press.

[5]

Hamamatsu Photonics, hhttp://www.hamamatsu.co.jpi.

[6]

Eljen Technology, hhttp://www.eljentechnology.comi.

[7]

Kuraray Co., LTD., hhttp://www.kuraraypsf.jpi.

[8]

H. Sugimura, et al.: Phys. Lett. B 729 (2014) 39-44.

[9]S.H. Kim, et al.: Nucl, Instr. and Meth, in press.

ELPH Annual Report, Tohoku University (2014)45(ELPH Experiment : #2781)

200 MeV/c 陽電子ビームを用いたシリコンストリップセンサー
および読み出し回路試作機の性能評価
西村昇一郎 1 , 池田博一 2 , 3 , 池野正弘 2 , 4 , 上野一樹 2 , 4 , 内田智久 2 , 4 , 川越清以 5 ,古浦新司 5 , 高力孝 2 , 4 , 齊藤直人 2 , 4 , 佐々木修 2 , 4 , 調翔平 5 , 田中真伸 2 , 4 , 東城順治 5 ,長澤翼 5 , 三部勉 2 , 4 , 吉岡瑞樹 5 , 他 J-PARC muon g − 2/EDM コラボレーション
1 東京大学大学院理学系研究科 （113-0033 文京区本郷 7-3-1）
2 Open-It （305-0801 つくば市大穂 1-1）
3 宇宙航空研究開発機構 （305-8505 つくば市千現 2-1-1）
4 高エネルギー加速器研究機構 （305-0801 つくば市大穂 1-1）
5 九州大学理学部 （812-8581 福岡市東区箱崎 6-10-1）
6 九州大学 RCAPP （812-8581 福岡市東区箱崎 6-10-1）

Evaluation of Test Silicon Strip Sensors and Readout
ASICs with the 200 MeV/c Positron Beam
Shoichiro NISHIMURA1 , Hirokazu IKEDA2 , 3 , Masahiro IKENO2 , 4 ,Kazuki UENO2 , 4 , Tomohisa UCHIDA2 , 4 , Kiyotomo KAWAGOE5 ,Shinji KOURA5 , Takashi KOHRIKI2 , 4 , Naohito SAITO2 , 4 ,Osamu SASAKI2 , 4 , Shohei SHIRABE5 , Manobu TANAKA2 , 4 , Junji TOJO5 ,Tsubasa NAGASAWA5 , Tsutomu MIBE2 , 4 , Tamaki YOSHIOKA5 ,and for the J-PARC muon g − 2/EDM collaboration
1

Faculty of Science, The Univ. of Tokyo, Hongo 7-3-1, Bunkyo-ku, 113-0033
2

3
4

Open-It, Tsukuba 305-0801

Japan Aerospace Exploration Agency (JAXA), Sengen 2-1-1, Tsukuba-shi, 305-8505

High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba-shi, 305-0801

5

Faculty of Science, Kyushu Univ., Hakozaki 6-10-1, Fukuoka-shi Higashi-ku, 812-8581
6

Kyushu Univ. RCAPP, Hakozaki 6-10-1, Fukuoka-shi Higashi-ku, 812-8581

The muon g − 2/EDM experiment at J-PARC (E34) aims to measure muon g − 2 with a precisionof 0.1ppm, and search for muon EDM with sensitivity down to 10−21 e · cm. In this experiment, muonis accelerated to the 300 MeV/c and injected to the storage ring that supplies a 3 T precise magnetic
field. We plan to measure a track of a decay positron by the highly-segmented positron tracking detector.
The tracker is required to have high rate capability, high stability against a large rate change, good
operation in a high magnetic field, and good position resolution. The silicon strip sensor is useful forour experiment. Two types of test sensors and test readout ASICs were produced and tested by the∗

Present address: Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826

46

ーム

3 T 一様磁場	

  

子ビ
V陽
e
G
3   μA
  333

直径 66 cm

ミュオニウム生成300  K〜25  m
eV

極冷ミ

ューオ
300M ンビーム
eV/c

物質生命科学実験施設 (MLF)
ミューオン基礎物理ビームライン (H-Line)
極冷 μ+ ビーム : 強度 106/sec
運動量 300 MeV/c (γ = 3)
pT/pL 〜 10-5
偏極度 > 50 %

第1図

ミューオン
蓄積リング

J-PARC E34 実験の全体概念図

200 MeV/c positron beam to check the signal-to-noise ratio and time resolution. As a result, signal-tonoise ratio satisfied the requirement of S/N>15 and time resolution was improved about twice by ToTtime walk correction.

§ 1 . 研究背景
ミューオンの異常磁気能率 (g − 2) はブルックヘブン国立研究所 (BNL) での E821 実験において 0.54ppmの精度で測定され、標準理論の予測値と 3.3σ の乖離がある [1]。また CP 非保存量であるミューオン電気
双極子能率 (EDM) についても探索が行われ、現在の上限値は 1.8 × 10−19 e · cm である [2]。J-PARC での新実験 (E34) では g − 2 を 0.1 ppm の精度で、EDM を 10−21 e·cm の感度での測定を目指している [3]。
第 1 図は J-PARC E34 実験全体の概念図である。本実験では 300 MeV/c まで加速したミューオンを 3 T
一様磁場、軌道半径 333 mm の小型蓄積リングに蓄え、崩壊陽電子の飛跡をリング内側にある飛跡検出器
により再構成し、ミューオンのスピン歳差運動を測定する。第 2 図は陽電子飛跡検出器の概念図である。陽
電子飛跡検出器には高レート耐性が求められ、シリコンストリップセンサーの使用を検討している。飛跡検出器は 48 枚のベーンと呼ばれる羽根板からなり、1 ベーンに 24 枚のシリコンストリップセンサーを搭載する予定である。 これまで飛跡検出器の主要部分となるセンサーの開発と読み出し回路の開発が並行して進行し、テストセンサーと読み出し回路試作機の製作、実験室での基礎的な性能評価を行ってきた。今回、その次の段階として、ビームを使ってセンサーと読み出し回路を接続した状態での性能評価を行った。

1.1 シリコンストリップセンサー
第 3 図はシリコンストリップセンサーの仕様である。センサーは軸方向と動径方向の位置をそれぞれ読み出すために 2 種類のセンサーを用い、それぞれ A センサー、R センサーと呼ぶ。共に厚さは 320 µm、p-on-nのシングルサイドで、バイアス抵抗は 10 MΩ である。この仕様に基いて、それぞれのセンサー 64 strip に相当するテストセンサーを製作し、基礎特性の測定を行った。第 1 表はテストセンサーの仕様である。また基礎特性評価の結果を第 2 表にまとめた。テストセンサーが問題なく動作することを確認し、仕様から予47  1"vane Frontend"
electronics  
!

r

r



(side"view)



T."Kohriki 

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ico

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576!mm!!333 !
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第2図

陽電子飛跡検出器の概念図

軸方向(A)センサー	

動径方向(R)センサー	

74mm（外寸）	

74mm（外寸）	
72mm(有感領域)	

ストリップ仕様	
  
間隔	
  	
  	
  100	
  um	
  
幅	
  	
  	
  	
  	
  	
  	
  	
  	
  	
  27	
  um	
  
長さ	
  	
  	
  	
  	
  	
  72	
  mm	
  
本数 1024	
  第3図

104mm（外寸）	
102mm（有感領域）	

102mm（有感領域）	

104mm（外寸）	

72mm(有感領域)	

ストリップ仕様	
  
間隔	
  	
  	
  188	
  um	
  
幅	
  	
  	
  	
  	
  	
  	
  	
  	
  50	
  um	
  
長さ	
  	
  	
  	
  102	  mm	  本数 384	
  シリコンストリップセンサーの仕様

48

第 1表

テストセンサー仕様
仕様
動径方向センサー 軸方向センサー
厚さ0.320 mmストリップ数64
読み出しストリップ
純アルミニウム
読み出しストリップ厚さ
1.5 µmストリップ間隔
0.188 mm0.100 mmストリップ長さ102 mm72 mm
ストリップ幅
0.050 mm0.027 mmストリップ間容量 (概算値)
約 6 pF
約 4 pF
第 2 表 基礎特性評価の結果
動径方向センサー
軸方向センサー
予想値
測定値
予想値
測定値
異常なし
異常なし
プラトー領域確認
プラトー領域確認
93 V
73 V
350 pF360 pF150 pF170 pF
6 pF
7.4 pF
4 pF
6.2 pF23.4 pF
15.9 pF仕様
目視確認
I-V 特性
完全空乏化電圧
バルク容量
ストリップ間容量
検出器容量

想される性能通りの結果が得られた。

1.2 読み出し回路
E34 実験では測定時間構造に特化した独自のフロントエンド ASIC(SlitA) を用いる。第 4 図は SlitA のブロックダイアグラムである。今回は Analog part の試作機を製作し (SlitA2013)、性能評価を行った [4][5]。第 5 図は製作した試作器の写真であり、32 チャンネルを同時に読み出すことができる。時間情報を測定するのに重要な項目として、ゲイン、ダイナミックレンジ、ノイズ (ENC)、パルス幅、タイムウォークの値を調べ、要求値と比較した。性能評価の結果を第 6 図にまとめた。この性能評価から概ね要求通りの性能が得られていることを確かめた。

Preamp+Shaper'Comparator'

TDC+(5ns+0me+stamp)'

InputsMemory+Read+
Controller+(40.96us+memory)'

Vth
CLK+
Write+Start+
Write+Busy+

Read+Ready+Read+Start+
Read+Busy+DAC

Analog+part'

第4図

Digital+part'

Processor'(Zero&suppress,+
edge+detec0on,+
Serializer)

Serial+Outputs++(100Mbps)

Real+0me+
Control+
Slow+control+
I/F+

Conﬁgure+
monitor

読み出し ASIC(SlitA) のブロックダイアグラム
49

test pulse in	variable
resistance	

2 cm	

10 cm	

analog monitor	

GND	

SlitA2013	

-0.9 V	+0.9 V	CLK SDI CLB( for digital control )	

+2.5 V	

digital out	

第5図ASIC 試作器 (SlitA2013) の写真 [5]SlitA2013 á×ãparameter

Requirement

MeasurementøïĢ'>'70'mV/MIP

~'50'mV/MIP

Ďğþ>

<100'ns

<'100'ns'(50'ns@1'MIP)

ăïĊĖąõĠĢý

5'MIP

>'5'MIPčïÿ@15pF

<'2000'e

1490'eĄĚĢČğO

128

64ĂïėðòĤõ<<'5'ns

15'ns

j®

5'mW/ch~'1.9'mW/ch

第6図

SlitA2013 の性能評価まとめ [5]

º¹

50

FS

BDC1 BDC2DSSD1Radialsensorfiber scint.

Axial
sensorSilicon-strip sensors
plastic scint.

DSSD2

fiber scint.

plastic scint.

BDC3 BDC4BSe+
EASIROCWFD (digitizer)
TDC
Trigger

第7図

ビーム試験時のセットアップ§ 2 . 研究目的
E34 実験では統計数と非対称度の関係から崩壊時のエネルギーが 200 MeV 以上の陽電子を信号とする。
SN 比に対する要求値は 15 以上であり、まず、実際の実験環境下での SN 比を見積もるために、200 MeV
陽電子の信号波形を測定する。さらに本実験では時間情報のずれが誤差に効果を与えるため、時間情報の広がりとして時間分解能を測定する。また同時に Time over Threshold (ToT) を測定し、タイムウォーク補
正がどの程度有効であるかを見積もる。

§ 3 . 実験セットアップ
第 7 図はビーム試験のセットアップである。テストセンサーのストリップ方向を x 軸、ストリップに
鉛直な方向を y 軸、ビーム方向を z 軸と定義する。試験目的である A センサーと R センサーを中心に、
陽電子飛跡を再構成するために Belle II 用 DSSD と、10 本の 0.5 mm 角と 6 本の 1 mm 角のシンチレー
ションファイバーからなる BDC4 台を設置した。さらにトリガー用のシンチレーターを最上流と最下流に設置し、それぞれ FS と BS と呼ぶ。FS のサイズは (x, y, z)=(6 mm,5 mm,1 mm)、BS のサイズは(x, y, z)=(12 mm,10 mm,10 mm) である。それぞれの検出器のデータ取得には、汎用 MPPC 読み出しモジュールである EASIROC で BDC の波高を測定、Waveform Digitizer (WFD, CAEN V1742) で DSSD、
テストセンサー、FS、BS の陽電子信号の波形を測定、TDC (CAEN V1190) でテストセンサーと FS、BSの陽電子ヒット時間を測定した。

§ 4 . 実験結果
4.1 実際の実験環境下での SN
第 8 図はビーム試験で得られたテストセンサーの典型的な波形と波高分布である。波高は BDC4 台でトラックが引けることを条件に課し、波形をフィッティングすることにより求めた。波高分布では最小イオン化粒子 (MIP) によるピークが観測され、波高は最頻値で A センサーで 88.0 mV、R センサーで 68.8 mVになり、SlitA2013 のゲインからセンサー上で生じた電荷量に逆算すると、A センサーで 2.1 × 104 e、R センサーで 1.7 × 104 e となった。これに対して J-PARC MLF において測定されたノイズの大きさは A セン
サーで σA = 1160e、R センサーで σR = 990e であったので、実際の実験環境下での SN 比は A、R それ
ぞれ、18.5、17.7 となり、要求値 15 以上を満たすことが分かった [6]。

51

hwaveV1742_0
A-‐‑‒sensor  CH16

hwaveV1742_1

wave  form  [mV]

100

251604

Mean

314.8

RMS

90.59

80
60
40
20
0
0

200

400

600

(b)	
 R-‐‑‒sensor  CH16

hwaveV1742_0
Entries

800

Entries

0

50

100

150

Pulse  height  (mV)

第8図

229.5

30
20
10
0
200

400

600

time  [ns]

800

1000

103

102

R_height_peaksearch
Entries
48566
Mean
6.937
RMS
15.3
r2 / ndf
117.1 / 113
Prob
0.3766
Constant
274.4 ± 11.2
MPV
68.81 ± 0.36
Sigma
5.346 ± 0.190

MPV	
  =	
  68.	  8	  [mV]	
  ＋  44017300   　        [e]­−  330

10

1

1
-50

236.5

RMS

40

104

MPV	
  =	
  88.0	
  [mV]	
  ＋  67021100   　        [e]­−  46010251604

Mean

R_height_PeakSearch

A_height_peaksearch
Entries
48566
Mean
6.296
RMS
14.11
r2 / ndf
108.4 / 97
Prob0.2019Constant
122.3 ± 6.5
MPV88.01 ± 0.61
Sigma
7.061 ± 0.341

102

Entries50(d)	
 R-‐‑‒sensor  CH16

A_height_PeakSearchA-‐‑‒sensor  CH16

103

60

Entries

(c)	

70

-10
0

1000

time  [ns]104hwaveV1742_1

80wave  form  [mV]

(a)	
120

200

250

-50

0

50

100

150

200

250

Pulse  height  (mV)(a), (b) テストセンサーからの典型的な波形、(c)、(d) テストセンサーの波高分布

4.2 テストセンサーの時間分解能
第 9 図はテストセンサーで測定された ToT と時間分布の関係を表している。時間の基準には時間分解能
が 140 ps の BS を使用した。また閾値はノイズの 5σ に設定した。ToT の違いによって 20 ns 以上のタイ
ムウォークがあることが分かる。タイムウォークによる広がりは SlitA2013 性能評価の結果と無矛盾である。この結果から、得られた ToT に対してタイムウォークによる時間の広がりを補正すると時間分解能が改善できると予想される。第 10 図はタイムウォーク補正前後でのテストセンサーの時間分布である。補正前は σA =3.6 ns、σR =5.6 ns であり、補正後は σA corr =2.4 ns、σR corr =2.6 ns となった。このことから

ToT によるタイムウォーク補正により、時間分解能が 1.5 倍から 2 倍改善し、実際の測定でも有効である
ことが分かった。

§5 . ま と め
J-PARC E34 実験ではミューオン g − 2 を 0.1ppm の精度で測定し、EDM を 10−21 e · cm の感度で探索することを目指している。実験に使用する陽電子飛跡検出器にはシリコンストリップセンサーの使用を検討しており、テストセンサーと読み出し回路試作機を製作した。信号となる 200 MeV 以上の陽電子に対する応答を調べるため、200 MeV/c の陽電子ビームを照射し、波形と時間を測定した。その結果、SN 比は実際の測定環境下において要求値 15 以上を達成することが見積もられた。また時間分解能は σA =3.6 ns、σR =5.6 ns であり、ToT によるタイムウォーク補正により σA corr =2.4 ns、σR corr =2.6 ns と一定の効果があることが分かった。タイムウォークは要求値よりも大きな値となっているが、この結果に対しては次期試作機である Slit128A において波高のゲインを増大させることにより、要求を達成する見込みである。

52

Prelim第9図

inary	

ToT と時間分布の関係

(a)	

(b)	

(c)	

(d)	

第 10 図Preliminary	

(a)、(b)ToT によるタイムウォーク補正前の時間分布、(c)、(d) 補正後の時間分布

53

謝

辞

本研究にあたって、石川 貴嗣さん、宮部 学さんを始め、東北大 ELPH の方々には大変お世話になりました。この場を借りて深く御礼申し上げます。

参
[1]

考

文

献

G. W. Bennett et al.: Final report of the E821 muon anomalous magnetic moment measurement
at BNL. Phys. Rev. D73, p. 072003, (2006).

[2]

G. W. Bennett et al.: Improved limit on the muon electric dipole moment. Phys. Rev. D80, p.
052008, (2009).

[3]

N. Saito et al.: Conceptual Design Report for The Measurement of the Muon Anomalous
Magnetic Moment g − 2 and Electric Dipole Moment at J-PARC, Conceptual Design Report(KEK), (2011).

[4]

K. Ueno et al.: IEEE Nucl. Sci. Symp. Conf. Rec. (2013)[5]

調 翔平、他: J-PARC ミューオン g − 2/EDM 実験:シリコンストリップ検出器用 ASIC の性能評価,

ICEPP Symp. 2014. (2014)[6]

長澤 翼、他: J-PARC muon g − 2/EDM 精密測定実験: シリコンストリップ検出器試作機のビームを用いた性能評価, 日本物理学会第 70 回年次大会 (2015)

54

ELPH Annual Report, Tohoku University (2014)(ELPH Experiment : #2784)

Performance evaluation of the readout electro circuit for the
PWO counters in the J-PARC E13 experiment
M. Nakagawa1 , N. Ichige2 , T. Koike2 , Y. Sasaki2 , H. Tamura2 , M. Ukai2 ,T. O. Yamamoto2 , and Y. Yamamoto2
1

Department of Physics, Osaka University, Toyonaka, 560-0043

2

Department of Physics, Tohoku University, Sendai, 980-8578

We are planning to perform a high-precision γ ray spectroscopy using the (K − , π − ) reaction in the
J-PARC K1.8 beam line (J-PARC E13). We use the PWO (PbWO4 ) scintillation counters in order tosuppress backgrounds in the γ ray spectrum from the excited states of Λ hypernuclei. At the same time,
we aim to obtain the inclusive missing-mass spectrum for Λ and Σ hypernuclei via the (K − , π − ) reaction
at the beam momenta of 1.5 GeV/c and 1.8 GeV/c.
Thus, the excited state of Σ hypernuclei will be produced. Especially, we expect the observation of
the excited state of Σ hypernucleus owing to a high momentum transfer. However, it could be difficult
to clearly distinguish the excited state whose natural width is broad from a large amount of background
events coming from the Σ quasi-free production in the missing-mass region. Thus, it is needed reducethe background coming from quasi-free events using energy deposit information of charged particles,
which originate in hyperon decay, in the PWO counters.
In order to obtain the energy information, a conventional QDC will be used. We have to consider
trigger latency of 1 µs in our DAQ system to obtain the ADC information. Then the analog signal of
PMT collecting photons from PWO crystals is delayed by the delay chip. The readout circuits using
three types of delay chips with different impedance (50, 100 and 300 Ω) were made in order to select thebest chip. The signal from PMT is divided at ratio of 10 : 1 to a TDC line for the background suppressor
and an ADC line for the energy measurement.
We tested the readout electro circuit at the electron beam line in the GeV-γ experimental area in
the Research Center for Electron Photon Science (ELPH), in June 2014. We performed the on-beamexperiment for performance evaluation of the ADC line and the off-beam experiment for performance
evaluation of the TDC line. As the result of performance evaluation under the on-beam condition, it wasdifficult to discuss the energy linearity of the PWO counter. We assumed the saturation effect was seenin the high energy deposit side in the spectrum. In addition, we checked the difference of performanceof the delay chips. The same energy resolution were obtained for all type of delay chips.
As the result of performance evaluation under the off-beam condition, performance deterioration of
the TDC line due to the splitting of the PMT signal and the insertion of the delay chips was not seen forthe detection of Compton scattered γ rays, which are backgrounds in a γ ray spectrum, in the off-beammeasurement using a 60 Co source.

55

As these results, we concluded that the performance of the PWO counters was not changed if weused the delay chips. We will use the 300 Ω impedance delay chip because of usability in making thereadout board.

§ 1. Introduction
The investigation of both Λ-N and Σ-N interaction is essential for the understanding of the YN
interaction in the S=-1 sector. However, the Σ-N interaction is not understood precisely yet due to lack ofexperimental data. A Σ particle is basically not bound in nuclei except for the 4Σ He hypernucleus because
the spin-isospin averaged Σ-nucleus potential is repulsive [1]. Then, the 4Σ He system was theoreticallyanalyzed in order to reveal the property of the Σ-N interaction in each spin-isopin state. However, since
the observed bound state was s-state (0+ ), only the contribution from the s-wave of the Σ-N interaction
was studied [2]. In order to extract the property of the p-wave, the experimental study of the exited stateof this system was suggested [3]. Therefore, experimental studies of the exited state of this system are
awaited in order to understand the property of the p-wave of the Σ-N interaction.
We are planning to perform a high-precision γ ray spectroscopy using the (K − , π − ) reaction in the
J-PARC K1.8 beam line (J-PARC E13) [4]. The purpose of the J-PARC E13 experiment is to obtain
the inclusive missing-mass spectrum for Λ and Σ hypernculei via the (K − , π − ) reaction at the beam
momenta of 1.5 GeV/c and 1.8 GeV/c. The wide momentum acceptance of the pion spectrometer named
the SKS-Minus system enables us to obtain such a inclusive spectrum. In addition, we simultaneously
measure γ rays from excited states of Λ hypernuclei using the germanium detector array, Hyperball-J.
In the J-PARC E13 experiment, a liquid helium target which is 3.0 g/cm2 in thickness, will be irradiatedwith high momentum K − beams. Hence, the momentum transfer will be changed from 200 MeV/c to500 MeV/c depending on the reaction angle. The production of the exited state of 4Σ He is expected. On
the other hand, the production of the ground state of 4Σ He is suppressed. Thus, an opportunity to study
the excited state of 4Σ He is given us by using the high-momentum K − beams for the first time. However,it could be difficult to clearly observe the excited state whose natural width is broad because of a large
amount of background events coming from the Σ quasi-free production in the same mass region. Thus,
it is needed reduce the background coming from quasi-free events using PWO (PbWO4 ) scintillation
counters used as a background suppressor in Hyperball-J system. The PWO counters are installedaround the germanium detectors to suppress background events in γ ray spectrum such as a Compton
scattering or hadron penetration. Since the energy of decay particles coming from the ΣN → ΛNconversion in Σ-hypernucleus and an escaped Σ particle in the quasi-free Σ production are different, weare able to reduce the quasi-free events by measuring the energies of the decay particles by the PWO
counters.

§ 2. PWO Counters
We introduce the PWO counters installed in the Hyperball-J system for the background suppression. The purpose of the germanium detectors is to measure the γ rays from the excited states of hy-

56pernuclei. The one of background source is Compton scattering events in the germanium crystals. The
PWO counters suppress the Compton background events by detecting γ rays originated from the Compton scattering. Hence, the germanium detectors are surrounded by the PWO counters.
The PWO counters consisted of PbWO4 crystals and PMTs. The major feature of the PWO crystal isshown in Table1. The PWO crystal is often used as a calorimeter because of thier high effective atomic
number and high density. The decay constant is 6 ns shorter than other inorganic scintillator. The
scintillation lights are one hundredth in comparison with a NaI scintillator. Since the PWO crystal at
the room temperature emits only 0.4 photo-electrons for 100 keV γ ray, we use the doped PWO crystal
and decrease its temparature in the J-PARC E13 experiment in order to increase the number of photon.

Table 1. Features of the PWO crystal [5]effective atomic number
density [g/cm3 ]radiation length [cm]decay constant [ns]photon number [NaI=100]
γ ray absorption [%]

76
8.28
0.89
6
1
67

Since the minimum energy of γ ray from the Compton scattering is as low as a few 100 keV, thethreshold of the discriminator is set to a few 10 keV in order to detect such a low energy γ ray. In
the original plan, we will use only the timing information for the background suppression . However,
the energy of decay particles shuld be also measured in order to reduce the background coming from thequasi-free Σ production in the missing-mass spectrum. In addition, the energy of decay particles emitted
from the hypernuclei and quasi-free Σ is as high as a few 100 MeV.
We need to understand the response of the PWO counters for high energy deposit. In addition, thechange of the performance of the PWO counters as the Compton suppressor when we obtain the TDC
and the ADC simultaneously.

§ 3. Readout electro circuit
In order to obtain ADC information, we have to consider trigger latency of 1 µs in our DAQ system.
Although we usually use cables to wait a trigger, it is not realistic to prepare cables for such a requirement because the number of channels of the PWO counters is 214. Hence, we use delay chips insteadof cables. In addition, when we use TDC and ADC simultaneously, the signal line has to be splited. If
a signal split ratio of the TDC line and the ADC line is 1 : 1, each signal height becames a half. In
this situation, it is difficult to be discriminated with 0.5 p.e. threshold without amplification because of
the small signal height. We have to keep the detection efficiency of the PWO counters as the Compton
suppressor. Thus, the split ratio of the TDC line and the ADC line is set 10 : 1.
Therefore, we prepared the electro circuit which splits signals and delay the signal in the ADC line.
Most of all circuits usually have the input impedance of 50 Ω. If there is a delay chip with the input

57

impedance of 50 Ω and the delay time of 1 µs, such a delay chip should be selected. However, such adelay chip is not available as commercial products. Hence, we prepare three kinds of the delay chips,with different input impedance as summarized in Table 2. In this paper, three delay chips are labeled as
Table 2. Properties of the delay chips

impedance [Ω]delay/chip [ns]number of chips

delay chips
50 100 300
100 300 1000
93
1

the 50 Ω delay chip, the 100 Ω delay chip and the 300 Ω delay chip, respectively. Since our DAQ system
require the delay time of 1µs, the number of needed delay chips are 9 for the 50Ω chip, 3 for the 100Ω
chip, and 1 for the 300Ω chip in each channel. We prepared three kinds of electro circuits using thesedelay chips. In order to suppress signal reflection, impedance matching is taken into account for eachcircuit.
The purpose of the test experiment is to decide the most suitable delay chip by checking the performance of three kinds of the circuits, and to study the change of the performance of the PWO counters as
a Compton suppressor.

§ 4. Experiment
We tested the readout electro circuit for the PWO counters with the beam and without the beamat the electron beam line in the GeV-γ experimental area in the Research Center for Electron Photon
Science (ELPH), in June 2014.
We used the electron beam whose size is 20 mm2 with the beam energy of 250, 450 and 650 MeV.
In this experiment, the PWO counters are not able to stop the electromagnetic shower caused by theelectron beam due to the small size of PWO crystals. The detectors used in this experiment, that is,
the Shower Veto counter (SV), the trigger counter (T1), and the PWO counters (PWO) are shown in Fig
1. SV rejected the shower events before T1. SV was a plastic scintillation counter which consisted ofa plastic scintillator whose size is 200×200×10 mm3 and the PMT. T1 was also a plastic scintillation
counter which consist of a plastic scintillator 10×10×5 mm3 and PMT. The PWO counters consisted of
the PWO crystal whose size of 40×200×20 mm3 and PMT. The DAQ system recorded TDC and ADC of
all detector with the T1 trigger. In addition, we also used FADC (Flash ADC) to record wave form. We
took data to study the difference of the performance of the three types of delay chips (and cable delay)using the electron beam of 450 MeV, and data to check the energy linearity of the PWO counter at thebeam energies of 250, 450 and 650 MeV.
We measured the change of the Compton suppressor performance using the NaI counters (NaI1 andNaI2) instead of the germanium detectors. Two NaI counters and three PWO counters were placed asshown in Fig 2. We used the radioactive source of 60 Co which emit the γ rays of 1173 and 1333 keV fromcascade decay. The data taking required NaI1 and NaI2 coinsidence trigger which the γ rays of 1173

58

Fig.1.

The schema of the setup for the performance evaluation using the electron
beam.

Fig.2.

The schema of the setup of the measurement using a 60 Co source without thebeam.

and 1333 keV irradiate NaI1 and NaI2 at the same time. In this measurement, ADC data for NaIs and
TDC data for PWO counters were taken with this trigger by changing delay chips. In addition, reference
data was taken without the ADC line of PWO counters.

§ 5. Analysis and result
In the analysis of data taken with the beam, we use the center segment of PWO counters as shownin Fig 1. In addition, we do not use data of SV because of almost no shower events after our analysis.
On the other hand, we use the three segments of PWO counters which is shown with shaded areain Fig 2 in the analysis of data taken without the beam.

The energy linearity
We took data at the beam energies of 250, 450 and 650 MeV. We used the 100 Ω delay chip in thismeasurement. The energy distribution for each data are shown in Fig 3. In addition, the correlation
between the beam energy and the mean value of each energy distribution are plotted in Fig 4. It isdifficult to discuss the energy linearity of the PWO counter. Then, we compare data of this experimentwith data of the Geant4 simulation. In addition, simulation data is convoluted with Gaussian by considering electric noise in the actual condition. As a result, the experimental data is not reproduced by
the convoluted simulation data. The experimental data have shorter tail structure in higher energy sidethan the simulation data. Thus, we assume the saturation effect is seen in the high energy deposit sidein the spectrum.

59

2000
0.022

1800

0.02

250 MeV

0.018

450 MeV

0.016

1600
1400

ADC [ch]650 MeV

a.u.

0.014
0.012
0.01
0.008

1200
1000
800
600

0.006
400

0.004

200

0.002
0
0

500

1000

1500

2000

2500

0
0

3000

ADC [ch]Fig.3.

The energy distribution for each beamenergy.

100 200 300 400 500 600 700 800

electron beam energy[MeV]Fig.4.

The correlation between the mean valueof each energy distribution and the beamenergy.

The difference of performance of the delay chips
We check the difference of the delay chips and cable delays as a reference. For this purpose, datataken with the beam energy of 450 MeV was analyzed. In Fig 5, the difference of performance of thedelay chips and the cable delay is shown. The horizontal axis is the normalized energy when setting thepeak value of the distribution for the cable delay to 1. In addition, the virtical axis is nomalized by the
number of the total events. The performance of 50 Ω delay chip is consistent with the performance of thecable delay whose impedance is 50 Ω. In addition, the gain of the 100 Ω delay chip is high. In contrast,
the gain of the 300 Ω delay chip is low.
As we mentioned in the previous section, the energy resolution of the PWO counter including theelectro circuit is not obtained by the energy distribution directly, because those energy distribution are
spread by the escape of a part of the electromagnetic shower. In order to obtain the change of the energy
resolution, we compared shape of each distribution by normalizing all the peak position to 1 as shown in
Fig 6. In addition, the virtical axis is nomalized by the number of the total events. Since all the shapesof distributions are the same, the energy resolution is not affected by delay chips.

The change of the Compton suppressor performance
We evaluated the effect to the TDC line, that is, the performance of the Compton suppressor fromour electro circuits by changing delay chips. We analyzed data taken without the beam. In this analysis,
the events lying around the photoelectric absorption peak of 1333 keV in the energy spectrum of NaI2
were gated in order to guarantee that γ ray of 1173 keV entered NaI1. Then, we check the energy
distribution of γ rays which is detected by NaI1. Here, the suppression factor is defined as the energy

60

0.03

0.03
cable

0.025

cable

0.025

50 Ω
100 Ω

0.02

300 Ω

0.015

0.01

0.005

0.005

0.5

1

1.5

2

2.5

0
0

3

Normalized energy
Fig.5.

The normalized energy distribution using delay chips and the cable when setting the peak position for the cable delay
to 1.

300 Ω

0.015

0.01

0
0

100 Ω

0.02

a.u.

a.u.

50 Ω

0.5

1

1.5

2

2.5

3

Normalized energy
Fig.6.

The normalized energy distribution
when setting all the peak position to 1.

distribution of NaI1 ratio of requiring PWO counters hits and not requiring it. The suppression factor isshown in Fig 7. No divide (no delay chip) for the reference is also shown in this figure. The suppression
factor is around 0.1 in Compton scattering region. The suppression factor decrease over 800 keV because
the γ ray which caused back scattering hardly entered the PWO counters. However, the γ ray whichcaused mutiple scattering often entered the PWO counters.
From these results, we estimated performance deterioration of the Compton suppressor by adding
our electro circuit. The change of Compton suppressor factor is defined as the ratio of the Compton
suppressor factor using dividers and no divide. The change is shown in Fig 8. The deterioration of theCompton suppressor performance is not observed in each delay chip blow 800 keV. On the other hand, it
is observed over 800 keV.

§ 6. Conclusion
We evaluted the three performances of the PWO counters. Although we were not able to obtain theenergy linearity in this experiment, the saturation effect was implied because experimental data and theGeant4 simulation result are in disagreement in the high energy side. As a result that the PWO counteris irradiated by same electron beam in each circuit, the performance of the delay chips is same, whose
gain is changed. The detection efficiency for the Compton scattering event is no affected by adding thereadout electro circuit for all the delay chips. As these results, we conclude that the performance of the
PWO counters is not changed if we use the delay chips. We will use the 300 Ω delay chip because ofusability of making the readout board.

61

PWO coinsidence ratio

0.7

Changing ratio of Compton suppressor

0.8
No divide
10 :1 divide (50 Ω)
10 :1 divide (100 Ω)
10 :1 divide (300 Ω)

0.6
0.5
0.4
0.3
0.2
0.1
0
0

7
6

10 :1 divide (100 Ω)

5

3
2
1

Energy of γ ray[keV]Fig.7.

10 :1 divide (300 Ω)4

00

200 400 600 800 1000 1200 1400

10 :1 divide (50 Ω)

200 400 600 800 1000 1200 1400

Energy of γ ray[keV]
Fig.8.

The PWO coinsidence ratio

The change ratio of the Compton suppressor performance

Acknowledgment
We would like to acknowledge the staff of the ELPH group for their efforts of keeping the stable
operation during the beamtime.

References[1]

T. Nagae et al.: Phys. Rev. Lett. 80 (1998) 1605.

[2]

T. Harada et al.: Nucl. Phys. A507 (1990) 715.

[3]

T. Harada et al.: Phys. Lett. B740 (2015) 312.

[4]

H. Tamura et al.: J-PARC Proposal E13, Gamma-ray spectroscopy of light hypernuclei (2006)
http://j-parc.jp/researcher/Hadron/en/pac 0606/pdf/p13-Tamura.pdf.

[5]

M. Ishii et al.: Prog. Crystal Growth and Charact.23 (1991) 245.

62

ELPH Annual Report, Tohoku University (2014)(ELPH Experiment : #2798)

Development of drift chamber for the J-PARC E21 COMET
experiment
H. Sakamoto1 , C. Wu2,6 , T. S. Wong1 , H. Yoshida1 , Y. Nakazawa1 ,H. Katayama1 , T. Yamane3 , T. Ueda1 , D. Tsunemori1 , N. Yokoyama1 ,H. Yong6 , A. Sato1 , Y. Kuno1 , J. Sato3 , Z. Zhang2 , R. P. Litchfield4 ,and P. Dauncey5
1

Department of Physics, Osaka University, Toyonaka, 560-0045
2

3

Institute of High Energy Physics (IHEP), China

Department of Physics, Saitama University, Saitama, 338-8570
4

University College London, UK
5Imperial College London, UK
6

Nanjing University, China

We carried out beam tests using prototypes of drift chambers for J-PARC E21 COMET experiment to measure gas gain, spatial resolution, and hit efficiency using three sets of gas mixtures,
He:iC4 H10 (90:10), He:C2 H6 (50:50), and He:CH4 (73:27) using two prototype chambers with sense wireof φ25 µm and φ30 µm. Results of the beam test analyzed by May 2015 are described in this report.

§ 1. Introduction
1.1 J-PARC E21
A neutrino-less muon-electron conversion process in muonic atoms that violates charged lepton
flavor is forbidden in the Standard Model (SM). Assuming massive neutrinos the probability to occur
this process would be about 10−52 , which is too small to detect. Some models beyond the SM predictthat probability to occur this process would be order of 10−15 . Current experimental upper limit of
the muon-electron conversion process had been set to be 7×10−13 by SINDRUM-II experiment at Paul
Scherrer Institute (PSI) in 1999. Signature of muon-electron conversion process in muonic atoms is
to detect mono-energetic electrons emitted from muonic atoms. Major background is electrons decayedin orbit (DIO) from muonic atoms, whose energy spectrum is continuous up to the energy of signal.
Therefore in order to achieve a high sensitivity a discrimination of DIO electrons is essential. J-PARC
E21 experiment (COMET) aims to search for the muon-electron conversion process with 10000 times
higher sensitivity than the current upper limit in two stages. The first stage (Phase-I) [1] will start from2017 with a single event sensitivity of 10−15 and the second stage (Phase-II) will start from 2020 with asingle event sensitivity of 10−17 . Schematic view of the beam line for Phase-I is shown in Fig.1.

63

1.2 COMET CDC
Cylindrical drift chamber (CDC) will be utilized to identify conversion electrons in Phase-I. CDC will
be installed at the end of the muon beam line around muon stopping targets as shown in Fig.2. COMET
CDC are required to measure momenta of electrons with an accuracy of about 200 keV/c (0.2%). Hit
occupancy is required to be less than about 10% to suppress pile-up effects. To achieve high resolution
on momentum measurement Helium-based gas mixture will be used to suppress multiple scattering.
Sources contributing to hit occupancy are protons after muon capture, gamma rays after muon capture,
DIO electrons, beam-related neutrons, and beam flash. Protons are easily discriminated using charge
information. Most of DIO electrons of low energy with a high intensity cannot reach CDC region of inner
radius of 50 cm. Beam-related neutrons and beam flash are suppressed by shielding around CDC.
A final design of the wire configuration had been determined in March 2014 according to comments
by IPNS reviewer. We had selected three gas mixtures of CDC in Table 1. In view of multiple scattering,
He:CH4 (80:20) prefers to others while in view of spatial resolution He:C2 H6 (50:50) prefers. In view ofshort drift time to reduce hit occupancy, He:C2 H6 (50:50) prefers.
Specification of sense and field wires is described in Table 2. Gas mixture and wire thickness are to
be determined by prototype tests.

Fig.1. Schematic view of beam line at Phase-I.
A pion capture solenoid, 90 degree muontransport solenoid, and detector solenoid
are installed.

Fig.2. Schematic view around CDC. CDC will
be installed under 1 T solenoid to measure momenta of conversion electrons
from muon stopping targets. [1]

1.3 Prototype Chambers
We have built three sets of prototype chambers. First prototype had been built in October 2013and cosmic-ray tests had been performed. Results of the cosmic-ray tests are described in the next
section. Second and third prototype has been built in November 2014 for a beam test. Main differencesof prototype I and II or III are stereo angle and field wire size. Prototype I and II are shown in Fig.4 andFig.5, respectively. Specifications of each prototype are summarized in Table 3.

64

Table 1. Comparison of different Helium-based low-Z gas mixtures, where X0 is the radiationIPlength, W is mean energy to generate one electron-ion pair, dE M IP /dx, nM
, and
T
M IP
np
mean is energy loss per cm, the number of electron-ion pairs per cm, and thenumber of primary ions per cm for minimum ionizing particles, respectively. [1]Gas
He:iC4 H10 (90:10)
He:C2 H6 (50:50)
He:CH4 (80:20)

X0 (m)
1310
630
2166

W (eV)
39
32
39

dE M IPdx(keV/cm)
0.88
1.63
1.47

IP
nM
(cm−1 )
T
29
60
17

IP
nM
(cm−1 )
p
14
27
11

Fig.3. Comparison of drift velocity as a function of electric fields in top and position-time relationship (XT curve) in bottom. [1]1.3.1 Cosmic-ray Tests by Prototype I
We have done cosmic-ray tests to measure spatial resolutions using prototype I without magnetic
fields and with uniform magnetic fields of 1 T with cooperation of KEK cryogenic group in summer of
2014. Trigger counters of 20×20 cm with Multi-Pixel Photon Counter (MPPC) readout were set in top
and bottom of the prototype. Four 64ch boards by REPIC with readout by optical cables were used toreadout data. For all of the gas mixtures spatial resolutions (including tracking errors) under 1 T were
measured to be less than 300 µm. The residual distribution is shown in Fig.6 and results on spatial

65

Table 2. Main parameters of the CDC [1]Inner wall

LengthRadiusLengthRadiusOuter wall
Number of sense layers
Sense wire

Field wire

Cell

Material
Diameter
Number of wires
TensionMaterial
Diameter
Number of wires
Tensionsquarestereo layer

1490.3 mm
496.0∼496.5 mm
1577.3 mm
835.0∼840.0 mm
20 (including 2 guard layers)
Au plated W
25 µm
4986
50 g
Al
80 µm
14562
70 g
16.2-16.8 mm in azimuthal, 16mm in radial+/- 70mrad

Table 3. Parameters of prototype chambers

Prototype No.
Sense wire
Field wire
Number of sense layers
Cell size
Stereo angle
Wire length
Wide angle coverage
Tension (sense, field)#/wires (sense, field)
Readout boardI
φ30 µm Au plated W
φ126 µm Al
11
15 mm (w) × 16 mm (h)aprox. 25 mrad
60 cm
30 deg.
50 g, 80 g
199, 602
64ch REPIC x4II
φ25 µm Au plated W
φ80 µm Al
11
16 mm (w) × 16 mm (h)aprox. +/- 70 mrad
20 cm
8 deg.
not measured
27, 72
48ch RECBE x1

III
φ30 µm Au plated W
φ80 µm Al
11
16 mm (w) × 16 mm (h)aprox. +/- 70mrad
20 cm
8 deg.
not measured
27, 72
48ch RECBE x1

resolutions are summarized in Table 5. In the cosmic-ray tests statistics were limited therefore we
proposed to carry out a beam test to study hit efficiencies effectively.

§ 2. Beam Test
Purpose of the beam test is to test following items with He:iC4 H10 (90:10), He:C2 H6 (50:50), and
He:CH4 (80:20) using prototype II (φ25µm sense wire) and prototype III (φ30 µm sense wire).
• Gas gain
• Position-time relation (XT curve)• Spatial resolution• Hit efficiency

66

Fig.4. Prototype I built at KEK
Fig.5. Prototype II built at Osaka University

Table 4. Parameters of the cosmic-ray tests at KEK [1]
Gas mixture
HV of sense layers
HV of guard layers
Vth
Magnetic Fields

Fig.6.

He:iC4 H10 (90:10)
1900 V
1200 V3790 mV
0 T, 0.6 T, 1.0 T

He:C2 H6 (50:50)
2600 V
1200 V3790 mV
0 T, 1.0 T

He:CH4 (80:20)
2150 V
1200 V3790 mV
0 T, 1.0 T

Residual distribution measured at the prototype chamber I with cosmic-rays [1]67

Table 5. Preliminary results on spatial resolutions measured by the prototype chamber [1]Gas mixture
He:iC4 H10 (90:10)
He:iC4 H10 (90:10)
He:iC4 H10 (90:10)
He:C2 H6 (50:50)
He:C2 H6 (50:50)
He:CH4 (80:20)
He:CH4 (80:20)

Magnetic Fields
0T
0.6 T
1T
0T
1T
0T
1T

Spatial Resolution
225.1 ± 11.2 µm
228.0 ± 9.7 µm
265.9 ± 18.0 µm
186.1 ± 7.6 µm
249.8 ± 16.3 µm
232.1 ± 91.5 µm
266.9 ± 59.4 µm

2.1 Setup
Momentum of electron beams was set to 460 MeV/c (Magnet current was set to 230 A). We used
Tungsten of a thickness of 0.2 mm as a converter. Two prototype chambers II and III are installed in
the beam line. Tracking chambers for reconstructing electron tracks were installed at upstream (T1X
and T1Y) and downstream (T2X and T2Y) of the prototype chambers. P10 gas was used for tracking
chambers. At the most upstream and downstream side scintillating counters of dimension of 30×30×3
mm and 30×30×5 mm were installed for making trigger signals. Distance of two scintillating counters
was about 80 cm. Scintillating counters were read out by 1-inch PMTs. Each of prototype and tracking
chambers was read out by a 48ch RECBE board developed by Belle II CDC group. In the underground
NIM modules for trigger logic and power supplies of detectors, gas system, and a DAQ-PC were set.
Trigger signal for monitoring trigger rates and Ethernet cable to log in the DAQ-PC were sent to theroom on the 1st floor. Power supply for the tracking chamber was 2ch manual controlled module and 4ch
remote controlled module by CAEN was used for prototype chambers. Schematic view of setup is shownin Fig.7.
2.2 Trigger Logic
Trigger signals were made by taking coincidence with the upstream and downstream PMTs. In
order to avoid a high hit rate VETO of 100 µs long after beam injection was added in the trigger logic.
Trigger signals were then delayed by 700 ns and sent to four readout boards. The diagram is shown in
Fig.8.
2.3 Readout Board
For readout of prototype and tracking chambers, 48ch RECBE boards shown in Fig.9 were used. A
RECBE board has eight ASD (Amp-Shape-Discriminator) chips, eight ADC chips, and a FPGA. Outputof the ASD are an amplified analog signal and discriminated digital signal. Threshold of discriminator iscommon to all of 48ch. The analog signal is digitized by the following ADC chips then ADCs are recordedby the FPGA in every 32 ns. The digital signal is sent to the FPGA and its rising edge is measured
using 1 ns clocks in the FPGA. Once a trigger signal is received ADCs and TDCs in a given window
size with a event header is sent to SiTCP [4]. SiTCP sends data through TCP to a DAQ PC. SiTCP also

68

Fig.7. Setup at beam test. Electron beam of 460 MeV/c pass thorough from left and triggeredby upstream and downstream PMT.

communicates through UDP to realize a slow control. Threshold, window size, and window position canbe set remotely by a slow control. In the beam test for the purpose of synchronizing clocks among four
RECBE boards an external clock of 62.5 MHz of 2.5 V was used. Window size was set as 1 µs.
2.3.1 Firmware
There are three versions of firmwares in the RECBE board; raw mode, suppress mode, and semisuppress mode. In raw mode, ADC and TDC at every 32 ns in a given window size for all channels
are sent to PC. In suppress mode, summed ADC in a given window size and first two TDCs only for hit
channels are sent to PC. In semi-suppress mode, all ADC in a given window size and first three TDCs
only for hit channels are sent to PC. In the beam test it was required to record waveform with keeping
data size small semi-suppress mode was used.

69

Fig.8. Trigger logic at beam test. Coincidence of two PMTs with 100 µs VETO is sent to four
RECBE boards [2]2.4 DAQ
DAQ-Middleware [5] developed by KEK online group was used to do online monitoring and savedata in storage.
2.5 Gas System
P10 gas was flowed to the upstream and downstream tracking chambers in series with about 50
cc/min. Helium gas was mixed with iC4 H10 or C2 H6 or CH4 using a mass flow controller by HORIBA.
Flow rate was set to 200 cc/min at gas exchange then reduced to 20 cc/min after gas exchange finished.
P10 and Helium-mixed gas lines were attached with each exhaust ports. In order to prevent backward
flow bubblers were set before exhaust ports after the run in Dec 7.
2.6 Measurements
Five shifts assigned for this beam test are scheduled as follows.
Dec 5 Beam tuning and trigger logic check.
Dec 6 Noise reduction of tracking and prototype chambers
Dec 7 Data taking of He:iC4 H10 (90:10)
Dec 9 Data taking of He:C2 H6 (50:50)
Dec 11 Data taking of He:CH4 (73:27) and He:iC4 H10 (90:10)

70

Fig.9. 48ch RECBE board developed by Belle II CDC group. Function is to amplifier signals andsample waveform and measure time of discriminated signals. Data is sent to DAQ PC via
SFP slot where either copper twisted cable or optical cable can be attached. External
clock and trigger signal are received from LEMO connectors or RJ-45. In the beam test
LEMO connectors are used. Test pulse input is used to test ASDs.

In the first day trigger rate was measured with adding VETO after beam injection to prevent hightrigger rate. With 100 µs long VETO a trigger rate was about 800 Hz. Efficiency of data taking was morethan 95% through runs. In the second day noise reduction of trigger and prototype chambers was performed mostly by improving grounding around chamber and RECBE boards. HV scanning and thresholdscanning of tracking chambers were performed. In the third day data taking of He:iC4 H10 (90:10) wasdone. HV scanning and threshold scanning were performed. As described in Section 3.1 we had problem
on ADC of prototype chambers therefore we requested one more shift at the end to take data of this day.
In the fourth day data taking of He:iC2 H6 (50:50) was done. HV scanning and threshold scanning were
performed. In the last day data taking of He:iCH4 (73:27) was done. Our proposed ratio of methane gas
was 20% but set to 27% by mistake. HV scanning and threshold scanning were performed. After thatdata taking of He:iC4 H10 (90:10) was carried out. In the last, we moved prototype chambers to take datawith different X positions and angles with respect to X axis and Y axis for testing dependency of cell
shape and beam direction.

71

2.7 Analysis and Results
2.7.1 Gas gain
Gas gain is calculated as below.
Gain =

Nt
,
Ncell
pair

Ncell
pair = Npair

dE celldE/dx

where Nt is the number of total electrons measured, Ncell
pair is the number of primary ions generated byan electron beam in a cell, Npair is the number of electron-ion pairs per cm, dE cell is an energy deposit
in a cell, and dE/dx is an energy deposit in a gas per cm. Npair and dE/dx are described in Table 1.
dE cell is calculated by G4beamline simulation [3] as shown in Table 6. Nt is calculated from a peak ofsummed ADC which is converted into charge using a calibration data as shown in Fig.10. Measured gas
gain curve for each gas mixtures at prototype II and III are shown in Fig.12.
Table 6. Parameters used in gas gain calculation [2]Gas mixture
He:iC4 H10 (90:10)
He:C2 H6 (50:50)
He:CH4 (80:20)

dE cell (keV/cell)
0.983
1.180
0.389

Fig.10. Relationship between input charge andsummed ADC taken by RECBE board
[2]

Ncell
pair (1/cell)
32.39
43.44
4.50

Fig.11. Summed ADC distribution afterpedestal subtraction of Prototype II
with He:iC4 H10 (90:10) at 1730 V [2]2.7.2 XT Curve
A method of measuring position-time relationship is as follows. Position is estimated as closest
approach of testing sense wire from an reconstructed track. In order to reconstruct tracks XT curve of
tracking chambers should be calibrated firstly. Three hits at the upstream and downstream tracking
chamber are used to make an track using a XT curve calculated by Garfield simulation. The track is
extrapolated to a testing wire of tracking chamber to make its XT curve. By fitting the XT curve of the72✁✂✄☎✆✝✁✂✞✟✠✄✡☛✌✁✂✄☎✆✍✁✂✟✄✠✦✁✂✄☎✆✦✁✂✟✧✄★

Gain Curve/He:C2H6=50:50 (PT2=25um PT3=30um)
Gain

Gain

Gain Curve/He:iC4H10=90:10 (PT2=25um PT3=30um)
105

105

Prototype2
Prototype2

Prototype3

104

Prototype3
104
1550

1600

1650

1700

1750

1800

1850

1900

1950

✌✁✂✄☎✆✍✁✂✟✄✠☞

2000 2050
HV [V]

2000

2100

2200

2300

2400

2500

2600

2700
HV [V]

Gain

Gain Curve/He:CH4=80:20 (PT2=25um PT3=30um)
106

Prototype2

105✎✏✑ ✎✒✑✓✔✕✖✕✖✗✘✙✚ ✛ ✚✜✢✣✓✔✕✖✕✖✗✘✙✤ ✛ ✤✥✢✣

Prototype3
2000

Fig.12.

2050

2100

2150

2200

2250

2300

2350

2400
HV [V]

Measured gain curve for each of gas mixtures. Gain of prototype II is roughly twice aslarge as that of prototype III [2]73

testing wire a new XT curve is estimated. Using the new XT curve track is again reconstructed andextrapolated to the testing wire. This iteration was done in three times. Chi-square distributions at
each of iteration are shown in Fig.13. The XT curve of T1X of wire#0 obtained after three iterations isshown in Fig.14.

Fig.13. Chi-square distributions of reconstructed tracks in X-axis at each
iteration steps.

Fig.14. XT-curve of wire#0 in T1X (upstream
tracking chamber) after iterations.

After that XT curves of all tracking chambers are calculated tracking was performed in each of X
and Y directions individually. Residual distributions on X and Y with different chi-square cuts are shownin Fig.15. From this figure cut of chi-square at 7 is applied. Tracking efficiencies of X and Y tracker areabout 50% so that net efficiency is about 25%.
Once X and Y positions at the upstream and downstream are determined, 3-dimensional track was
made. Using the 3D-track closest approaches to wires at prototype chambers are calculated finally. XT
curve of the prototype II of the central wire is shown in Fig.16.

Fig.15. Residual distribution on X (left) and Y (right) for different chi-square cuts.

74

wire#46
T [ns]

800

400

700

350

600

300

500
250
400

200

300
150
200
100
100
50
0
-10

-8

-6

-4

-2

0

2

4

6

8

10
X [mm]

0

Fig.16. XT curve of prototype II measured with He:C2 H6 (50:50) at 2500 V (Run#169).

2.7.3 Spatial Resolution
Measured time is converted to position Xmeas using the XT curve. Residual is calculated by subtracting Xmeas from reconstructed X position. Spatial resolution is estimated by fitting the residual
distribution with Gaussian distribution. The residual includes tracking errors. Fittings are done ineach range of drift distance from 0 mm to 8 mm in 1 mm steps. Residual distribution measured with
He:C2 H6 (50:50) is shown in Fig.17. Finally spatial resolutions in eight regions are averaged. At small
drift distance a spatial resolution becomes worse due to statistics of primary ions, while at large drift
distance it is due to a diffusion and an uncertainty of XT curve.

120
250

center = -0.118487, reso = 0.292453

500

center = -0.107227, reso = 0.198879

eff 0.6 = 2677.000000/2911.000000 = 0.919615

100

eff 0.6 = 6528.000000/6652.000000 = 0.981359

200
eff 2 = 2895.000000/2911.000000 = 0.994504

700

center = -0.048905, reso = 0.148461

eff 0.6 = 4364.000000/4534.000000 = 0.962506

400

eff 2 = 4526.000000/4534.000000 = 0.998236

center = 0.008729, reso = 0.135350

eff 0.6 = 8126.000000/8227.000000 = 0.987723

600

eff 2 = 6643.000000/6652.000000 = 0.998647

eff 2 = 8222.000000/8227.000000 = 0.999392

500

80
150

300

100

200

50

100

400

60
300
40
200

20
100

0
-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

4-5mm

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

5-6mm

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

6-7mm

0.5

1

1.5

2

70

240

500
600

0

7-8mm

220
center = 0.027672, reso = 0.148407

center = 0.007230, reso = 0.157428

center = 0.005711, reso = 0.176024

center = -0.040960, reso = 0.167807

60

200
400

eff 0.6 = 7667.000000/7854.000000 = 0.976190

500

eff 0.6 = 6248.000000/6357.000000 = 0.982854

eff 0.6 = 3391.000000/3503.000000 = 0.968027

eff 0.6 = 809.000000/845.000000 = 0.957396

180
50
eff 2 = 7830.000000/7854.000000 = 0.996944

eff 2 = 6323.000000/6357.000000 = 0.994652

eff 2 = 3478.000000/3503.000000 = 0.992863

160

eff 2 = 829.000000/845.000000 = 0.981065

400
300

140

40

120
300
30
100
200
80
200

20
60
100
40

100

10

20
0
-2

Fig.17.

-1.5

-1

-0.5

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0
-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Residual distributions measured with He:C2 H6 (50:50) at 2500 V (Run#169). Residual
distribution is fitted with Gaussian distribution in range of drift distance from 0 mm to
8 mm in 1 mm steps

75

2.7.4 Hit Efficiency
Hit efficiency is defined as the ratio of the number of events within 0.6 mm of residuals to thenumber of reconstructed events. Finally hit efficiencies in eight regions are averaged. Hit efficiency
as a function of HV for each gas mixtures are shown in Fig.18. Efficiency of He:iC4 H10 (90:10) and
He:C2 H6 (50:50) is about 95% while that of He:CH4 (73:27) is smaller than 95%. It is found that efficiency
drop found at higher HV is due to oscillation of waveform. Details are explained in Section 3.2.

✁✂✄☎✆✝✁✞✟✠✡☛✄☞☛✌
Average Efficeincy in Proto Type 3 (C H10)44Efficiency (D <0.6 mm)

3720
3730

0.9

3740
3750
3760

0.8

3770
3780

res

res

Efficiency (D <0.6 mm)

Average Efficeincy in Proto Type 2 (C H10)
1

0.7
0.6

1

0.8
0.7
0.6

0.5

0.5

0.4

0.4

0.3

0.3

0.2

0.2
128

0.1

243
136250 137
241
227 140228
102
230
240
143
239
238

132

134

110

0

3700
3720
3730
3740
3750
3760
3770
3780
3800

0.9

1300

1400

1500

249
248
247

141

1600

1700

231

232

234

1800

1900

126
124
123
122

0.1

236

246
245
244

0

2000
2100
High Voltage [Vote]

250
141242
227

110
128

132

134

1500

1600

249
248
247

228 140102
230
240
136239 137
238

231

232

234

236

237

246
245
244

135

116

1300

1400

1700

1800

1900

2000
2100
High Voltage [Vote]

Average Efficeincy in Proto Type ✁✂✄✆✍✁✎✠✏☛✄✏☛✌
2 (C H6)
Average Efficeincy in Proto Type 3 (C H6)
2

Efficiency (D <0.6 mm)

3730
3740

0.9

3750
3760

res

res

Efficiency (D <0.6 mm)

2

1

3770

0.8

3780

0.7
0.6

1

3740

0.9

3760
3770
3780

0.7
0.6
0.5

0.4

0.4

0.3

0.3
0.2

0.1

178
194

0

3750

0.8

0.5

0.2

3730

154

1800

155

156

1900

157

2000

158

159

2100

160

161

2200

163

183
182
181
193
179
164

168

2300

2400

169

188
187
186
192
184
172

0.1
194

0

2500
2600
2700
High Voltage [Vote]

155

1800

156

1900

157

2000

158

159

2100

160

161

2200

163

183
182
181
193
179
164

168

2300

2400

171

188
187
186
192
184
172

2500
2600
2700
High Voltage [Vote]✁✂✄✆✁✝✠✑✒✄✓✑✌
Average Efficeincy in Proto Type 3 (CH )4
4
Efficiency (D <0.6 mm)

3750
3760

0.9

3770
3780
3790

0.8

3800
3810

res

res

Efficiency (D <0.6 mm)

Average Efficeincy in Proto Type 2 (CH )
1

0.7
0.6

0.8

3760
3770
3780
3790

0.6
0.5

0.4

0.4

0.3

0.3
0.2
225

0.1
0
1900

3750

0.7

0.5

0.2

Fig.18.

1
0.9

209

2000

208

198

2100

201

202

2200

203

220
226
218
217
216
215
204

2300

0.1
205

2400
2500
High Voltage [Vote]

0
1900

223
210

209

2000

208

198

2100

201

202

2200

203

218
217
216
215
204

2300

205

206

207

2400
2500
High Voltage [Vote]

Efficiency curves measured with prototype II (left side) and III (right) for gas mixturesof He:iC4 H10 (90:10) (top), He:C2 H6 (50:50) (middle), and He:CH4 (73:27) (bottom). Linesof different colors indicate different thresholds of the RECBE boards.

2.8 Results of Spatial Resolution and Hit Efficiency
Results of spatial resolution and hit efficiency are summarized in Table 7.

76

Table 7. Results of spatial resolution and hit efficiency of prototype II and III for each gas mixtures where hit efficiency is maximum.
Prototype
II
III
II
III
II
III

Gas mixture
He:iC4 H10 (90:10)
He:iC4 H10 (90:10)
He:C2 H6 (50:50)
He:C2 H6 (50:50)
He:CH4 (73:27)
He:CH4 (73:27)

HV
1900 V
1900 V
2550 V
2550 V
2300 V
2300 V

Spatial resolution
191 µm177 µm178 µm
182 µm188 µm186 µmHit efficiency
95%
95%
97%
96%
92%
93%

2.9 Conclusion
We measured spatial resolution to be less than 200 µm including tracking errors for all gas mixturesand both prototype chambers. Efficiencies of about 95% were measured for all gas mixtures and bothprototype chambers. These results suggests that both φ25 µm and φ30 µm can be used as sense wire.

§ 3. Investigation of Issues Found in Prototype II and III
3.1 Strange ADC Distribution
We found that ADC distributions of both of prototype chambers II and III showed spike structuresin runs taken on Dec 7 as shown in Fig.19. ADC of tracking chambers looked fine so we thought RECBE
board had no problems. We continued to taking data since TDC distribution of prototype chambers
seemed normal. We didn’t put a bubbler at the gas exhaust line by Dec 7, therefore we tried to put abubbler after the shift on Dec 7 finished. We still saw strange ADC distributions in the morning runs on
Dec 8. ADC distributions showed suddenly normal after the next run when DAQ crashed. We thoughtthat the problem was fixed by adding the bubblers at that time. By off-line analysis after the beam test
we found that ADC distributions are normal. Therefore we conclude that this problem would be causedby bugs somewhere in online analysis or Middleware.

☞✌✍ ✎✏ ✑✒✓✔✕✖✒✗
Trigger/Event Rate [kHz]y [mm]

Trigger/Event Rate

1.2
1
0.8
0.6
0.4
0.2
0
0

100

Drift Time @ TX1

Trigger Rate
Average : 0.825 kHz
Event Rate

500

300

400

700
600

-400

-300

RECBE1_TDC26

-200

-100

RECBE1_TDC35

0

100

200

RECBE1_TDC19

300

TX2

300

1.4
1.2
1
0.8
0.6
0.4
0.2
0

-800

3

2

10

7000

7500

8000

8500

0
-1000

9000

10

3

700
600

0

2

7500

RECBE2_TDC35

8000

8500

0
-1000

9000

RECBE2_TDC19

200

-200

0

0
6000

6000

7500

8000

8500

9000

0
6000

6500

RECBE1_ADC47

7000

7500

8000

8500

9000

0
6000

7500

8000

8500

9000

0-1000140

0 -1000

8000

-400

-200

0

0-1000

-800

-600

-400

-200

0

0
6000

7000

7500

8000

8500

9000

40

140

0 -1000

6000

100
80

-600

-400

-200

0

0-1000-800

RECBE1_TDC43

-600

-400

-200

0

0
6000

7000

7500

8000

8500

9000

0
6000

9000

7000

7500

8000

8500

9000

0
6000

6500

RECBE1_ADC43

7000

7500

8000

8500

9000

0-1000

-400

-200

0

0 -1000

-800

-600

-400

-200

0

0-1000-800

RECBE2_TDC43

6

60

5

50

-600

-400

-200

0

0
6000

4

40

3

30

7000

7500

8000

8500

9000

0
6000

2000

1

-800

-600

-400

-200

0

0 -1000

-800

-600

-400

-200

0

0-1000

-800

-600

-400

-200

0

0
6000

6000

6000

4000

4000

2000

7500

8000

8500

9000

0
6000

6500

RECBE2_ADC43

7000

7500

8000

8500

9000

8500

9000

RECBE2_ADC27
20000
18000
16000

14000

14000

12000

12000
10000
10000

80

6500

7000

7500

8000

8500

9000

0
6000

2000

6500

7000

7500

8000

8500

9000

0
6000

2

20

1

10

8000
8000

60

6000

7000

7500

8000

8500

9000

0-1000

-800

-600

-400

-200

0

0 -1000

6000

4000

4000

5000
20

6500

✘✁✂ ✄☎ ✆✝✄✞✄✞✟✠✡ ☛☛ ✁✂ ✄☎ ✆✝✄✞✄✞✟✠✡ ☛☛Fig.19.

9000

5000

7000

18000
16000

15000

100

40

0-1000

8500

10000

6500

RECBE2_ADC25

20000

120

8000

10000
4000

50

8000

25000

3
100

7500

RECBE2_ADC11

5000

6500

RECBE2_TDC27
180
160

10000

8000

20

7000

15000

10000

2000

-600

RECBE2_TDC25

14000

12000

140

10000

6000

10

6500

20000

20000
15000

20
-800

RECBE1_ADC27

14000

12000

2

0
6000

30000

20

40
20

6500

RECBE1_ADC25

8000

150

8500

25000

6000

12000

10000
200

40

8000

35000

4000

40
2000

6500

RECBE1_TDC27
300

250
5
4
30

7500

RECBE2_ADC3

60

4000

4000

2000

20

-800

60
6
50

7000

30000

25000

8000

80
60

40

2000
0

2000
6500

35000

12000

10000

60

50

-200

RECBE1_TDC25

0
6000

RECBE2_ADC47
14000

80

100

6000
4000

20

7

4000

2000
6500

RECBE2_TDC11
100

10000

60

100

60

6000

6000
4000

-600

RECBE2_TDC3

200
180

8000

40

9000

4000
2000

-800

220

160

8000

8500

8000

8000

10000

6000

0

8000

RECBE2_ADC19

10000

10

5

-200

7500

16000
14000
12000

20
-400

7000

14000
12000

120
6000

6500

18000
16000

10000

120

12000

80

200
150

80

2

6000

14000

15

80

-600

RECBE2_TDC47

160
140

10000

120
100

9000

12000

40

-800

180
12000

16000
14000

8000

0

25

60

7000

RECBE1_ADC11

18000
10000

-200

RECBE2_ADC35

24000

20000

20

40

6500

RECBE1_ADC3
20000

-400

18000

120
100

100

2000

7000

-600

16000

140
120

4000

6500

12000

8500

TY2-0
TY2-1
TY2-2

22000
30

20
-400

-800

RECBE2_ADC26

35

180

80

-600

RECBE1_TDC11

8000

1
7000

160
140

2000

-800

120

100

7500

3

10

6500

60

0-1000

10

400

6000

180

4000
4000

2000

0

7000

4

200

-200

RECBE2_TDC26

8000

6500

ADC Sum @ TY2

10

100

240

6000

-200

6000

10

300

-400

200

2
-400

300

250

0

10

-600

220
200
180
160

-200

TY2-0
TY2-1
TY2-2

1

10000

8

-600

RECBE1_TDC3

-400

800

160

350

-600

Drift Time @ TY2
900

TY1-0
TY1-1
TY1-2

500
10

-800

8000

4

-800

RECBE1_TDC47-800

ADC Sum @ TY1

200

RECBE1_ADC19

6000

8000

6

0 -1000

6500

4

100

10

40
20
0

1

6000

10

300

12000

10000
14
12

0

500

0
-1000

RECBE1_ADC35

16

160
140

-200

TY1-0
TY1-1
TY1-2

400

80

-200

-400

700

60
50

240

-600

600

10000

100
100

-400

TX2-0
TX2-1
TX2-2

4

200

1
0
-1000

800

220

120

150

500
z [mm]

12000

18

180
200

400

RECBE1_ADC26

20

220
200

-600

10

10

Drift Time @ TY1
TY2

250

-800

10

400
300

100

500
600
Elapsed Time [sec]PT2

Hit Rate [kHz]PT300-1000ADC Sum @ TX2

TX2-0
TX2-1
TX2-2

800

2

10

200

TY1

-50

-400

Drift Time @ TX2

TX1-0
TX1-1
TX1-2

3

500
10

100

100

TX1

50

-600

10

300

200

-100
-500

-800

10

4

400

Hit Rate Map

0-1000ADC Sum @ TX1

TX1-0
TX1-1
TX1-2

600

-800

-600

-400

-200

0

0-1000

2000
-800

-600

-400

-200

0

0
6000

6500

7000

7500

8000

8500

9000

0
6000

2000
6500

7000

7500

8000

8500

9000

0
6000

6500

7000

7500

8000

✘✁✂ ✄☎ ✆✝✄✞✄✞✟✠✡ ☛☛☛ ✁✂ ✄☎ ✆✝✄✞✄✞✟✠✡ ☛☛☛Display of online monitor for Run#147 taken in the last on Dec 7. Summed ADC distributions of prototype II and III showed strange structures.

77

3.2 Oscillation after Signal
When HV increased we observed similar XT curves at left and right hand side as shown in Fig.20.
It seems that these dummy XT curves has some correlation with real one. It is found that hits on thesedummy XT curves appear when a beam passes neighboring wires. When a neighboring wire has a signal
an induced current of opposite sign is flowed in the central wire. Since induced current is opposite sign
to signal it cannot be triggered. But as shown at top in Fig.21 waveform is oscillating just after the firstsignal arrived therefore it could be triggered. We found that pulse height of the oscillation increased
when pulse height of signal increased. This is the reason to see dummy XT curves on both sides of thereal XT curve. This effects make a precision of time measurement worse, resulting in expanding widthof residual distribution. This is why an efficiency became small when HV increased as seen in Fig.18.
This oscillation is reproduced by measurements using 90 Sr with prototype chamber II and III at
Osaka University. See bottom of Fig.21. After several trials such as enforcing shielding around RECBE
board and end plates at HV side we successfully eliminate this oscillation by shielding signal cables fromfeed through to the RECBE board. Since shielding around end plates at prototype II and III seems not
sufficient external noise would be picked up into the signal cables. We are planning to test the oscillation
with a next prototype chamber IV where end plates are perfectly covered with aluminum boxes.

Fig.20. Sense wire positions around beampassing area (top). XT curve measured at higher HV setting. Dummy XT
curves are seen at both sides.

Fig.21. Oscillation seen at the neighboring
sense wire at the beam test (top). Reproduced oscillation using prototype
chamber at Osaka University using
90
Sr beta source. (bottom)

78§ 4. Wire Size Decision after the Beam Test
Results of the beam test show good efficiencies of 95% and good spatial resolutions less than 200µm for all of gas mixtures. From aging point of view, past experiments suggest to keep electric fields
on the surface of field wires to be below 20 keV/cm not to accelerate aging speed. Magnitude of electricfields is mostly determined by size of field wire. In case of φ80 µm (prototype II and III) 20 kV/cm isreached at 1700 V, while in case of φ126 µm (prototype I) voltage can be increased up to 2600 V. Frombeam test results, efficiency at 1700 V is too small in case of He:C2 H6 (50:50) and He:CH4 (73:27). Even
with He:iC4 H10 (90:10) an efficiency was around 90%, which still be less than the maximum efficiency of
95%. It is strongly recommended to follow this rule, therefore we had determined to use φ126 µm as
field wire instead of φ80 µm. Size of sense wire had been chosen as φ25 µm in terms of suppressing
multiple scattering and Lorentz angle. We have made a next prototype chamber IV using sense wire of
φ25 µm and field wire of φ126 µm. Cosmic-ray tests under 1 T magnetic fields and beam test under 0 T
using prototype IV are planned.

Acknowledgment
We would like to thank all members in ELPH for assistance and supporting kindly our beam test.

References[1]

COMET collaboration, Technical Design Report, http://comet.kek.jp/Documents files/PAC-TDR2014/PAC-Review-20141110.pdf[2]

Y. Nakazawa et al., COMET Phase-I CDC Prototype Beamtest 1, 70th JPS meeting at Waseda
University, Mar. 21 2015[3]

http://www.muonsinternal.com/muons3/G4beamline[4]

http://research.kek.jp/people/uchida/technologies/SiTCP/[5]

http://daqmw.kek.jp

ELPH Annual Report, Tohoku University (2014)

79(ELPH Experiment : #2800)

Development of a photon tagger with counters based on
MPPCs
Hiroki Kanda1 , Takao Fujii1 , Yu Fujii1 , Manami Fujita1 , Hiroki Homma1 ,Kazuhisa Honda1 , Takatsugu Ishikawa2 , Masashi Kaneta1 , Yuma Kasai1 ,Chigusa Kimura1 , Junichiro Kusaka1 , Kazushige Maeda1 , Sho Nagao1 ,Satoshi N. Nakamura1 , Aki Ninomiya1 , Takashi Nishizawa1 , Kazuki Nochi1 ,Keiichi Ozeki1 , Takayuki Sasaki1 , Hajime Shimizu2 , Yuta Takahashi1 ,Kyo Tsukada1 , Ryouun Yagi1 , Fumiya Yamamoto1 , and Hirohito Yamazaki2
1
2

Department of Physics, Tohoku University, Sendai, 980-8578

Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826

We have been developing an internal photon tagger for the NKS2 experiment. Its electron detector
consists of scintillation counters based on Multi-Pixel Photon Counter (MPPC) with newly developed
read-out systems. The electron detector including a part of counter units was installed in a bending
magnet (BM4) of BST ring and tested with a beam. Obtained time resolution was less than 40 ps in
Gaussian σ at hit rates ranging from a few kHz to 200 kHz. A tagging efficiency was roughly 70%,
which is consistent with the tagging efficiency obtained with STB Tagger. Further development andproduction are being continued.
We have been studying the meson photoproduction on deuteron with tagged photon beams and Neutral Kaon Spectrometer 2 (NKS2) at the Research Center for Electron Photon Science (ELPH), Tohoku
University. NKS2 is a magnetic spectrometer for a charged particle detection. We have provided uniquedata in the neutral kaon photoproduction [1–3] and charged pion photoproduction [4] on the deuteron.
We continue data analyses for kaon photoproduction [5] and double pion photoproduction [6–8].
We have been upgrading the electron detector of the photon tagger [9]. The electron detector detects
momentum analyzed electrons after the bremsstrahlung and thus define timing and energy of radiatedphotons. By increasing number of channels of the electron detector, we aim at increasing its granularityand enlarging an energy range of tagged photon beams. With 1.3 GeV electron, a range of tagged photon
energy is from 0.82 to 1.28 GeV with energy spans ranging from 1 to 6 MeV. The new electron detector
consists of scintillation counters based on Multi-Pixel Photon Counters (MPPCs) supplied by Hamamatsu Photonics K. K. with newly developed read-out systems [10, 11]. We designed a electron detectorof the photon tagger composed of counter units each of which has four position defining counters (TagF)
and one timing counter (TagB). By a coincidence of a TagB counter and one of TagF counters, a trajectory of an electron can be selected to reduce an electromagnetic background from electrons, positrons or
gamma rays coming from other sources.

80

In the first experiment, two counter units were aligned along a trajectory of scattered electrons
after the bremsstrahlung. Thus their timing properties in the same environment as an actual electron
detector of the tagger were measured. The prototype detector case were placed along a vacuum chamberof the accelerator in the pole gap of the bending magnet, BM4. We measured time resolutions of the TagB
counters by electrons sequentially passing through them. In this measurement, we supposed identical√time resolution for the two TagF counters. The time resolution was obtained as s 1/ 2 of a sigma of a
fitted Gaussian to a time difference distribution between two TagBs. It exhibits that the time resolution
is dependent on the bias voltage and its tuning is important (Fig. 1(a)). Sufficiently good time resolution
and its weak dependence to the hit rate were obtained at 200 kHz which is the maximum expected hit

Time Resolution (ps)Time resolution (ps)rate (Fig. 1(b)).
50

(a)
45
40
35

50

(b)
45
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35

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25

20
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74

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76

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40

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80

100 120 140 160 180 200

TagB1 Single count rate (kHz)

Fig.1. Time resolution of TagB (a) with regard to a bias voltage and (b) with regard to a hit rate.

In the second experiment, we fixed three counter units on an actual detector case which were placedin BM4. We tested a tagging efficiency of three counter units with a lead glass Cherenkov counter (LG)which was placed at the downstream of tagged photon beam line. The electron energy was set as 1.3
GeV. The tagging efficiency (ϵtag ) was defined as a following equation:
ϵtag (Ee′ /Ee ) =NLG⊗Bi ⊗Fj
NBi ⊗Fj (Radiator ON) − NBi ⊗Fj (Radiator OFF)(1)

where Ee′ is an expected electron energy detected by a coincidence of i-th TagB and j-th TagF, Ee is theincident electron energy, NLG⊗Bi ⊗Fj is a number of hits on LG in coincidence with i-th TagB and j-th
TagF and NBi ⊗Fj is a number of coincident hits on i-th TagB and j-th TagF in each measurement period.
The combinations of ith-TagB and j-th TagF in true coincidence for both STB Tagger and the present
setup are 4(i − 1) + 1 ≤ j ≤ 4i, where i and j are natural number. STB Tagger consisted of 12 TagBs
and we placed 3 TagBs in our test setup. Description of ”Radiator ON” and ”Radiator OFF” in braces
denote a status radiator motion. A remnant gas bremsstrahlung contributes to ”Radiator OFF” hits, but
it is known to be less than a few percent of ”Radiator ON” hits in the previous studies of STB Tagger.
In our measurement, it was ignored to obtain the tagging efficiency. The obtained tagging efficiencies
are smaller tagging efficiencies obtained with STB Tagger at Ee = 1.2 GeV (Fig. 2). In general, thetagging efficiencies obtained with STB Tagger in the small Ee′ /Ee region are likely to be smaller than

81
those in a Ee′ /Ee ∼ 0.2 region. This tendency is caused by Mϕller scattered electrons, which does notemit photons but creates background hits to the electron detector. By considering this tendency, present
tagging efficiencies are consistent with the ones obtained with STB Tagger. Detailed analyses of hits on
the counters revealed that the coincidence of a TagF and a TagB effectively selects electrons after the

Tagging efficiency

bremsstrahlung.

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0

Ee = 1.2 GeV (2006)
TagB1 E e = 1.3 GeV
TagB2 E e = 1.3 GeV
TagB3 E e = 1.3 GeV

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Ee' / EeFig.2. Tagging efficiency dependent on a ratio of a detected electron energy to an incident electron energy. Black circles show the efficiency measured with STB Tagger and coloredmakers show the efficiency measured with current setup. Red squares show the efficiency
with TagB1 hit required; green triangles, with TagB2; blue diamond, with TagB3.

We assembled all the counter units and mounted them on the detector case (Fig. 3).

Fig.3. Photograph of the detector case of the tagger with all the counter units mounted on it.

Auxiliary circuits for signal transfer and data taking are being designed and developed. We continue
working to complete the development of the new tagger. We plan to finish its commissioning in FY2015.

82

Acknowledgment
We would like to thank the administration and technical staff in ELPH and the faculty of science.
This program was partly supported by Core-to-core program (21002), strategic young researcher overseas visits program for accelerating brain circulation (R2201), and KAKENHI Grant Number 23540334
by JSPS.

References[1]

K. Futatsukawa et al.: EPJ Web of Conferences 20 (2012) 2005.

[2]

B. Beckford et al.: arXiv:1308.1649.

[3]

M. Kaneta et al.: JPS Conf.Proc. 1 (2014) 013071, M. Kaneta et al.: Nucl.Phys. A914 (2013) 69-73.

[4]

Y. C. Han et al.: Nucl. Phys. A834 (2010) 596c-598c.

[5]T. Fujii et al.: Proceedings of J-PARC2014, to be published.

[6]

C. Kimura et al.: Few Body Syst. 54 (2013) 1319-1322.

[7]

F. Yamamoto et al.: JPS Conf.Proc. 1 (2014) 013072.

[8]

H. Kanda et al.: JPS Conf.Proc. 1 (2014) 013075.

[9]

H. Yamazaki et al.: Nucl. Instr. and Meth. 1 (2000) 10.

[10] T. Nishizawa et al.: IEEE trans. Nucl. Sci. 61 (2014) 1278.
[11] H. Kanda et al.: Conference Record, Nuclear Science Symposium and Medical Imaging Conference(NSS/MIC), 2013 IEEE.

ELPH Annual Report, Tohoku University (2014)83(ELPH Experiment : #2802)

Test experiment of a prototype RICH counter for the
J-PARC E50 experiment
T. Yamaga1∗ , R. Honda2 , T. Ishikawa3 , K. Kato4 , M. Naruki4 , H. Noumi1 ,K. Shirotori1 , and T. Takahashi1
1Research center for nuclear physics, Osaka University, Osaka, 567-0047
2

3

Department of physics, Osaka University, Osaka, 567-0047

Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826
4

Department of physics, Kyoto University, Kyoto, 606-8502

In this experiment, we tested MPPC photo-detection plane for RICH counter. A prototype RICH
counter has been constructed and tested with electron beam at GeV-γ experimental hall. The Cherenkov
angle and its angular resolution was measured at different beam momentum, mirror set angle andrefractive index of radiator. Clear Chrenkov ring was observed by selecting Chrenkov photons, andtypical angular resolution was 3.0 mrad. As a results, MPPC can be used as photon sensor of RICH
counter.

§ 1. Introduction
We are planning an experiment for studying charmed baryons via the p (π − , D ∗− ) reaction at the
J-PARC high-momentum beam line [1]. Charmed baryons will be measured by a missing mass method.
Scattered D ∗− will be reconstructed by selecting its decay chain of D ∗− → D̄ 0 π − → K + π − π − . Decay
particles from D ∗− and produced charmed baryon which have momenta of up to 16 GeV/c are detectedby large acceptance spectrometer system. Particle pass is tracked by drift chambers located around
dipole magnet, and its time of flight is measured by TOF wall. Particle identification (PID) is performedby using TOF and forward PID counter. The cross section of the p (π − , D ∗− ) Λc is estimated to be at alevel of nb. On the other hand, the cross section to produce at least a kaon in the final state is a few
mb. A huge amount of events including K + and two π − s will be able to be reduced by identifying not
only D ∗− but also D̄ 0 . However, wrong identification of those particles increases a background level
drastically. For example, wrong identification of positive pions or protons with positive kaons enhances
the background level by a factor of about 20. Therefore, a high performance of the PID counter is desired
for the charmed baryon spectroscopy. We designed a Ring imaging Cherenkov (RICH) counter with
two radiators, aerogel and C4 F10 gas of refractive indices of 1.04 and 1.00137, respectively, in order to
identify pions and kaons in a wide momentum range from 2 to 16 GeV/c [2]. The RICH counter contains
radiators, photo-detection plane and focusing spherical mirror. Because the RICH counter is located at
the most down stream of the spectrometer system, the counter size must be large to cover all acceptance.

∗

Present address: Research center for nuclear physics, Osaka University, Osaka, 567-0047

84

The PID performance of RICH counter is determined by angular resolution of the Cherenkov angle which
depends on position resolution of photo-detection plane. In order to obtain enough resolution with large
acceptance, 2 pieces of photo-detection plane which have size of 1.0 × 2.0 m constructed by more than2000 photon sensors is needed.
We plan to use the multi-pixel photon counter(MPPC) as a photon sensor. The MPPC can detect 1
photon with very nice separation which is advantage to detect feeble Cherenkov photons. Furthermore,
it is not affected by magnetic field as compared to the PMT. However, larger dark current rate of the
MPPC which is typically 100 kHz/mm2 may increase noise hit. Consequently, the PID performance may
become worse.
In this experiment, performance of a prototype RICH counter using MPPC photo-detection plane isstudied.

§ 2. Experimental setup and procedure
2.1 SetupThis experiment was performed at GeV-γ experimental hall. Electron beam which has momentumof up to 700 MeV/c was induced to a prototype RICH counter. Electrons which passes center of thecounter is selected by trigger counters located upstream and down stream of the prototype RICH counter.
2.2 Prototype RICH counter
The prototype RICH counter contains a MPPC photo-detection plane and a focusing spherical mirror (see Figure 1). In this time, we used S12642-0808 module made by Hamamatsu Photonics. It has 64
segments (8 × 8), and each segment is size of 3.1 × 3.1mm2 . The total detection area is 25.8 × 25.8 mm2 .
The spherical mirror is used for focusing the Cherenkov photons and transferring photons to photodetection plane. The curvature radius of mirror is 330 mm which was determined by size of detection
area. The reflection surface is made by Aluminum which has reflectance of about 90% in visible light.
Air and CO2 are used for radiator which has refractive indices of 1.000293 and 1.0005, respectively.
The detector box is filled by each radiator one by one. Then, we can change Cherenkov angle even same
particle velocity. The length of radiator can be modified from 90 cm to 190 cm by moving photon shieldplate.

§ 3. Results
Figure 2 shows TDC distribution of photo-detection plane. In this experiment, two TDC informationof leading and trailing edge of the signal were acquired. However, only leading timing is used in thisanalysis.
Clearly peak corresponding to Cherenkov photons is observed. In this analysis, time cut with 50
ch. window is used to separate between Cherenkov light and dark current. The hit pattern of photondetection plane is shown in Figure 3. The Cherekov ring can be observed and S/N ratio become better byselecting the Cherenkov peak in TDC distribution.

85

Fig.1.

Prototype RICH counter. (left) Overview of the Prototype RICH counter. Electron beam
comes from left side. (middle) MPPC photo-detection plane. MPPC is mounted on readboard. (right) Spherical mirror.

80000
70000
60000
50000
40000
30000
20000
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8

Y segment

TDC timing distribution. A peak around 300 ch. is came from Cherenkov photons. Red
and blue regions indicate cut window for Cherenkov photons and background from darkcurrent, respectively.

Y segment

Fig.2.

Pat
Entries 352875
Mean x 3.726
Mean y 3.817
RMS x
1.717
RMS y
1.735

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Entries
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Fig.3.

2

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63216
3.654
3.552
2.467
2.313

8

X segment

Hit pattern of photon-detection plane. (left) Cherenkov region is selected. The Cherenkov
ring is clearly observed. (right) Dark current region is selected. There is no ring structure.

The Cherenkov angle is calculated by simple equation,


Rring
θc = Tan−1
Rmir

(1)

86

, where Rring and Rmir are radius of the Cherenkov ring and spherical mirror, respectively. Actually,
incident angle of particle must be taken into account to calculate the Cherenkov angle. However, because particles which passes center of the RICH counter are selected, incident angle is fixed to be 0
degree for all event. All detected position in one triggered event are converted to the Cherenkov angle, then all of them are averaged to determine the measured Cherenkov angle for a particle. Figure
4 shows the Cherenkov angle distribution. There is clear peak around 25 mrad which corresponds toθAir = Sin−1 (1/β n) = 24 mrad, where β is particle velocity which is fixed 1.0 and n is refractive index
of air. On the other hand, there is no peak structure when dark current region is selected. We canseparate events from Cherenkov photons and dark current by using TDC timing. The angular resolution is obtained by a peak width in the Chrenkov angle distribution. In this time, evaluation of angularresolution is performed by using RMS value of the Cherenkov angle distribution.
Each data set are analyzed by the same way and evaluated its angular resolution.

500

ThetaMean
Entries31959
Mean
0.02583
RMS 0.003158

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Entries31959
Mean
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RMS 0.009291

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0.000

Average Cherenkov angle (rad)Fig.4.

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Average Cherenkov angle (rad)Average Cherenkov angle distribution. (left) Cherenkov region is selected. A peak fromCherenkov photons is clearly observed around 25 mrad. (right) Dark current region is
selected.

3.1 Incident momentum dependence
Due to multiple scattering of incident particles, the angular resolution may becomes worse. We
studied this multiple scattering effect by changing incident momentum of the electron beam. The angular resolution with electron momentum of 300, 500 and 700 MeV/c is measured. Figure 5 shows
angular distribution at each incident momentum. The angular resolution does not depend on incident
momentum. So, the effect from multiple scattering is small.
3.2 Geometry dependence
The spherical mirror is used for focusing the Cherenkov photons to improve angular resolution.
Actually, the focusing by spherical mirror is not completely parallel to point focusing when mirror angle
against incident particle becomes large. In order to evaluate this effect, set angle of mirror is changed.

87

ThetaMean

1800

ThetaMean

Entries 123941
Mean
0.02584
RMS 0.003831

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Entries31959
Mean
0.02583
RMS 0.003158

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Average Cherenkov angle (rad)Fig.5.

0.030

0.035

0.040

0.045

0.050

Average Cherenkov angle (rad)Average Cherenkov angle distribution at each beam momentum. (left) and (right) figures
are Cherenkov angle distribution at beam momentum of 300 MeV/c and 700 MeV/c,
respectively.

The angular distributions at each set angle are shown in Figure 6. In this case, radiator and incident
momentum are fixed to be air and 700 MeV/c, respectively. As a results, angular resolution doesn’t
depend on mirror set angle so much.

1200

ThetaMean

1000

Entries72564
Mean
0.02574
RMS 0.003131

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ThetaMean

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Mean
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RMS 0.002671

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Average Cherenkov angle (rad)Fig.6.

0
0.000

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0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Average Cherenkov angle (rad)Average Cherenkov angle distribution at each mirror angle. (left) and (right) figures are
Cherenkov angle distribution at mirror angel of 5 deg. and 12.5 deg., respectively.

3.3 Radiator dependence
In this experiment, because of only electron beam was used, the Cherenkov angle is fixed to be
the maximum value even electron momentum is changed. Actually, the RICH counter identifies particles by measuring different Cherenkov angle from each particle. To investigate separation between
different Cherenkov angles, we change refractive index of radiator. The refractive indices and calculated Cherenkov angles are listed on Table 1. Figure 7 shows the Cherenkov angle distribution for eachradiator. The difference of Cherenkov angle between radiators is clearly observed.

88

Table 1. Refractive indices and calculated Cherenkov angles for each radiator
Radiator
AirCO2n1.000293
1.0005θc (mrad)
24.2
31.6

0.025

Air
Entries57102
Mean
0.02478
RMS 0.002813

0.020

CO2
Entries 102997
Mean
0.02865
RMS 0.002127

0.015

0.010

0.005

0.000
0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Average Cherenkov angle (rad)Fig.7.

Average Cherenkov angle distribution with each radiator. Blue and Red spectra are
Cherenkov angle distribution with Air and CO2 radiator, respectively.

§ 4. Summary
The prototype RICH counter which has MPPC photo-detection plane was tested by using electron
beam. Angular resolutions at each incident momentum, mirror set angle and radiator index were measured. As a results, MPPC photo-detection plane was useful for the RICH counter. More detail analysis
is now ongoing.

Acknowledgment
We would like to thank staffs of ELPH for their supports and providing exellent experimental condition.

References[1]

H. Noumi et al.: J-PARC E50 proposal,
http://www.j-parc.jp/researcher/Hadron/en/pac 1301/pdf/P50 2012019.pdf[2]

T. Yamaga : Master’s Thesis, Osaka university (2014)

ELPH Annual Report, Tohoku University (2014)89

Study for the charged particle detector using wave length
shifting fibers and MPPC
M. Miyabe1 , T. Abe1 , Y. Inoue1 , M. Sasagawa1 , Y. Honda1 , T. Ishikawa1 ,S. Kido1 , T. Suda1 , Y. Tajima2 , and A. O. Tokiyasu1
1Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826, Japan2

Department of Physics, Yamagata University, Yamagata 990-8560, JapanThe study for baryon spectroscopy and meson photo-production experiment has been carried out
with an electro-magnetic calorimeter FOREST and BGOegg at Research Center for Electron Photon
Science (ELPH), Tohoku University. High energy gamma detector is generally consists of inorganic
scintillators and charged particle identification detectors like plastic scintillators. However, the space forthe charged particle identification detector is often limited in the design process of the large acceptanceelectro-magnetic calorimeter. In this study, we developed a hodoscope detector using a plastic scintillator,
wave length shifting fibers and multi-pixel photon counters. This hodoscope is designed for the charged
particle detectors surrounding the 90mm-diameter Liquid Hydrogen target system to be installed inside
BGOegg. It is produced by a 5mm-thickness plastic scintillator, which is covered by the wave length
shifting fibers with the diameter of 1mm. Each 4 and 8 fibers are connected to multi-pixel photon
counters. The position resolution of the hodoscope was examined by the positron beam at ELPH, Tohoku
University. As a result of the analysis, we achieved the position resolution σ = 1.17mm with the 8mm
interval read out.

§ 1. Introduction
The study of baryon resonance is one of the effective tool to understand the low energy Quantum
chromodynamics (QCD). A nucleon excited by the incident particle emits mesons like π, η and K, andthen de-excited to the ground state nucleon. With the detection of these emitted mesons, we study the intermediate state of these reactions. On these mesons, π 0 and η immediately decay into two gamma. Withhigh accuracy measuring these high energy gamma, BGOegg enables detailed studies for the baryon resonance. A large acceptance electro-magnetic calorimeter BGOegg include the charged particle detectors
on the inside(Fig.1). BGOegg is an egg-shaped gamma ray detector which consists of 1320 BGO inorganic crystal scintillators of 220 mm in length (equal to 20 radiation length). BGOegg has 22 layers andcovers from 24 degrees to 144 degrees at polar angle. Each layer has 60 crystals and covers 360 degrees
at azimuthal angle. The energy resolution for the positron at 1GeV is 1.3% and the position resolution
amounts to 3 mm. These values are the highest performance in the world [1, 2]. To detect the gamma
with high accuracy, charged particle detectors which has the equivalent position resolution are necessary. In this study, we developed and evaluated the charged particle detector using wave length shifting

90

fibers and multi-pixel photon counters for this purpose.
420

BGOegg200

319

Target cell φ90
165

24 o

200φ

36 o

charge detector

460
295

1320 BGO blocks
Elphs Lab
1.9t

Fig.1. Cross Section view of BGOegg crystals and charged particle detectors§ 2. Design of the detector
BGOegg has an egg-like-shape and consists of 1320 BGO inorganic crystal scintillators. BGOegg
also include the target system and the charged particle detectors on the inside. For our Liquid Hydrogentarget system has the 90 mm diameter and the smallest diameter of BGOegg is almost 200mm, thesecharged particle detectors have to cover the large acceptance and must not interfere BGOegg. In thepresent setup of BGOegg experiment, we use the cylindrically-located 30 plastic scintillators for the
charged particle identification. But in this detectors only, we could not obtain the z position of a charged
particle at all. To avoid this situation, we adopt the design which has a plastic scintillator covered bywave length shifting fibers with reasonable intervals and tilt angle. In this design, we could obtain not
only ϕ-direction information but also the z position information. Figure2,3 shows the overview of thehodoscope consist of a plastic scintillator and wave length shifting fibers. The emitted light from thecharged particle passed the plastic scintillator, are absorbed by the fibers at the surface of scintillator,
and re-emitted with the long wave length light. Re-emitted light propagate to the photon detectors
inside of wave length shifting fibers. Considering the efficiency of absorption, emission and the loss ofthe propagation, the number of photons at the photon detectors are very small(about a few photons).
Therefore, the efficiency of the conversion from light to electric signal is important. For this reason, we
adopt the multi-pixel photon counter as the photon detectors.
2.1 Plastic Scintillator and Wave Length Shifting (WLS) fibers
In this study, we use the wave length shifting (WLS) fibers Y-11 manufactured by Kuraray corporation [3]. The absorption wave length of Y-11 is about 430nm, emission wave length is 476nm. Y-11 has
the multi-cladding configuration, Center core, Inner cladding and Outer cladding are polystyrene(index
n=1.59), polymethylmethacrylate(n=1.49) and Fluorinated Polymer(n=1.42) respectively. An attenuation length is 3.5m. The base plastic scintillator of our hodoscope is EJ-212 [4] made by ELJEN Tech-

91

e+

θ

WLS fibers

Rear surface fiber
Front surface fiber
plastic scintillator

plastic scintillator

Fig.2. Overview of the photon detection with
Plastic Scintillator and WLS fibers

Fig.3. A simple design for 2 sided WLS
fiber hodoscope

nology. The plastic scintillator is covered by 128 WLS fibers in both side. Each 8 fibers are read out by
multi-pixel photon counter. Total number of channels is 16.
2.2 Multi-Pixel Photon Counter (MPPC)
Multi-Pixel Photon Counter (MPPC) is a recently well-developed photon counting device. MPPC isconsist of many Geiger mode avalanche photo-diode (APD) and shows the high performance for photon
counting. MPPC can be operated with low voltage and don’t affected by the Magnetic field. For theefficiency of the photon detection will achieve the 40% with increasing the supply voltage, it is suitable
for the low light yield detectors like this study. In addition, its small size and simple read out system of
MPPC has advantage in the restricted geometry. In this study we use the S12572-050P manufactured
by Hamamatsu Photonics [5]. The acceptance surface, pixel pitch, number of pixels, wave length of the
maximum sensitivity are 3 × 3mm, 50µm, 3600 and 450nm respectively. These parameters are suitable
for the light from WLS fibers. We use the 16 MPPC and 8 WLS fibers connect to each MPPC. Figure 4
shows the accomplished hodoscope picture. The plastic scintillator and WLS fibers were glued by EJ-500,
WLS fibers and MPPC were fixed by the special handmade jig and the optical grease.

Fig.4. The double sided 16ch hodoscope without MPPC

92

§ 3. Experiment
The hodoscope detectors were tested by the positron beam at ELPH, Tohoku University. The experiment was carried out during a day at March 2014. We changed the position of positron beam by moving
the detectors and signal conversion circuits inside of the light shielded black box. Beam profile monitor(BPM) which consist of 32 scintillating fibers(3 × 3mm) are located in upstream of the hodoscope. In
the downstream of hodoscope detectors, a plastic scintillator with 10 × 10mm and 5mm-thickness were
set up. Figure 5 shows the experimental setup.
Using the 4 scintillating fibers around the center of BPM and the downstream plastic scintillator, we
made the trigger signals. From these trigger position information, we specified the position of the penetrated positron. We obtained the ADC and TDC data of all hodoscope channel. Output signal of MPPC
went through the 160ns cable delay and input the photomultiplier amplifier (×10). After the amplifying,
the signals were connected to LeCroy 2249W(ADC) and REPIC RPC-060(TDC). Using these digitizeddata and beam position information, we estimate the position resolution of the hodoscope detector. In
this experiment, irradiation position of beam is 13 point, 2mm interval for x and y direction, and we took
1000 event data at each position. We also took the pedestal data with the clock gate for ADC calibration.
A typical trigger rate was about 2Hz.
Positron Beam

BPM
Black Box

6mm
40mm

Fiber - MPPC

7mm
400mm

TRIGGERPS

5mm

Fig.6. figure of the experimental setup

Fig.5. Overview of the detectors setup.

§ 4. Result and Discussion
At the first, we calculated the ADC distribution for each hodoscope channels with subtraction thepedestal value. These ADC distribution are fitted by the Moyal distribution function. As a result offitting, we obtained the light output of hodoscope channels. Figure 7 shows the typical ADC distribution
and the result of fitting. Figure 8 shows this obtained light output as a function of the distance fromthe positron beam. This light output distribution has a little fluctuation caused by the difference in thegain of each MPPC. After the correction of this fluctuation, we fitted the light output distribution with

93

Fig.7. ADC distributions from the hodoscope channels. The solid line shows the Moyal distribution function.

athe Lorentzian f (x) = 1+( x−c(Fig.9). The position dependence of the light output is well described)2b

Fig.8. Light output distributions as afunction of the distance from thebeam center.

Fig.9. Normalized light output distributions as a function of the distancefrom the beam center.

by the Lorentzian function. The fitted width value(b) of Lorentzian is about 4.4mm. With fixing thisfitted value b, the light output distribution is fitted by Lorentzian per event. As a result of this fitting,
we can estimate the beam center position(c) from the light output. From the Gaussian fitting for the
residual distribution of the reconstruct position and the beam position, we obtained the width σEXP =2.09 ± 0.04mm.
By the way, experimental result σEXP is related to the resolution σBP M of the beam position detector(BPM). We assume the relation as below,
2
2
2
σEXP
= σHOD+ σBP
M√
where, σBP M = 2 × 3/ 12, so the position resolution of our hodoscope detector σHOD
σHOD = 1.17 ± 0.04mm
is obtained.
In the case of the previous design (Fig.3), the z-direction position resolution is estimated with σz =

94

Fig.10. Residual distributions of the reconstruct position(X) and beam position(X0 ). The solidline shows the fitting result of the Gaussian distribution function.

1.17/ sin θ. On the other hand, the z position resolution of BGOegg itself at the hodoscope position isestimated with σBGO = 3.1 × rHOD /200 mm. For example, we suppose that rHOD and θ are 100mm
and 60◦ , the accomplished z position resolution σz is good enough compared to σBGO . Where θ is definedas the angular of z-axis and WLS fibers and rHOD is the inner radius of the hodoscope.

References[1]

T. Ishikawa: Internal GeV-γ Analysis Note No. 231B (2011)[2]

T. Ishikawa: Internal GeV-γ Analysis Note No. 238B (2012)[3]

http://kuraraypsf.jp/psf/ws.html[4]

http://www.ggg-tech.co.jp/maker/eljen/ej-212.html[5]

http://www.hamamatsu.com/jp/ja/4004.html

ELPH Annual Report, Tohoku University (2014)95

The performance study of an electro-magnetic calorimeter
BGOeggY. Matsumura1 , T. Ishikawa1 , M. Miyabe1 , N. Muramatsu1 , H. Shimizu1 ,H. Hamano2 , T. Hashimoto3 , S. Kido1 , S. Masumoto4 , K. Mizutani3 ,K. Ozawa5 , T. Shibukawa4 , K. Shiraishi1 , A. Tokiyasu1 , N. Tomida3 , N. Tran2 ,Y. Tsuchikawa1 , H. Yamazaki1 , R. Yamazaki1 , and M. Yosoi2
1

Research Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826
2

Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047
345

Department of Physics, Kyoto University, Kyoto 606-8502

Department of Physics, University of Tokyo, Tokyo 113-0033

Institute of Particle and Nuclear Studies, High Energy Accelerator Research
Organization(KEK), Tsukuba, Ibaraki 305-0801

We are carrying out a meson photoproduction experiment at the SPring-8/LEPS2 facility. One of
the main purposes of the experiment is to search for η ′ mesic nuclei. The peak structure of the formationof η ′ mesic nuclei will be observed in the missing energy spectrum of forward protons in the C(γ, p)X
reaction. To reduce background events, we plan to tag the decay products of an η ′ mesic nucleus by usinga large acceptance electro-magnetic calorimeter BGOegg. BGOegg can detect γ’s coming from mesons
with a high energy-resolution and a high position-resolution.
We have started to collect physics data with a carbon and a polyethylene target from 2014. We
have performed energy and timing calibration of BGOegg and evaluated its performance. After theenergy calibration, we can observe the peaks corresponding to π 0 , η, and η ′ mesons in the γγ invariant
mass distribution with high mass-resolutions of 6.7, 14.4 and 18.8 MeV, respectively. In this report, thecalibration status and the performance of BGOegg are presented.

§ 1. Introduction
An η ′ meson has larger mass than other pseudo scalar mesons due to the UA (1) anomaly effect. Ina high-density environment such as nuclear medium, the η ′ mass is expected to decrease significantly
by partial restoration of chiral symmetry. By a theoretical calculation based on the Nambu-Jona-Lasinio(NJL) model, the decrease of an η ′ mass is estimated to be ∼150 MeV at the normal nuclear density(Fig.1 [1]). The large mass shift of the η ′ meson will cause a strong attractive potential in a nucleus, andwill result in a bound state of an η ′ and a nucleus. This is called an “η ′ mesic nucleus”.
We are carrying out an experiment to search for η ′ mesic nuclei at the SPring-8/LEPS2 facility
using a multi-GeV photon beam. η ′ mesic nuclei are searched for in the missing energy spectrum of theC(γ, p)X reaction, where proton momenta are measured with TOF-RPCs. Figure.2 shows a theoreticalprediction of the spectrum [1]. If η ′ mesic nuclei are formed, some peak structure will appear below

96

Fig.1. Theoretical prediction of mass shift of pseudo scalar mesons in a high-density environment based on NJL model. ρ0 is the normal nuclear density. [1]the η ′ production threshold in the missing energy spectrum. However, there will be a lot of background
events such as a multi-π production reaction with only proton detection, and S/N ratio is estimated to beapproximately 1/200. To reduce background events, we plan to tag the formation events of η ′ mesic nuclei
by detectiong particles in the final state with a large acceptance electro-magnetic calorimeter BGOegg.
η ′ N → ηN conversion is assumed as a tagged process, and the η is identified by detecting γ’s by using
BGOegg. To identify mesons in final state effectively, BGOegg is required to achieve a high resolution.
We have performed the energy and timing calibration of BGOegg, and have studied the mass-resolution
and the time-resolution achieved as a result of the calibration.

Fig.2. The expected spectrum of the 12 C(γ, p)11 B⊗η ′ as a function of the excited energy. E0 is theη ′ production threshold energy. The imaginary part of the optical potential is assumed tobe W0 = −5 MeV. [1]§ 2. LEPS2 beamline and BGOegg calorimeter
The experiment is carried out at the SPring-8/LEPS2 beamline (Fig.3). The photon beam is produced by backward Compton scattering with an ultra violet laser injected onto the 8 GeV electron beam

97in the strage ring of SPring-8. We can use a tagged photon beam with energies from 1.3 to 2.4 GeV,
which can produce nearly recoilless η ′ mesons. The beam intensity is now about 2 MHz with 4 lasers
injection. We have started to collect physics data from April 2014.

Backward Compton scattering
8 GeV electron
Recoil electron(tagging)

Laser~135 mLEP(GeV γ -ray)

LEPS2 Tagger
BGOeggLEPS2
spectrometer

Beam dump

Fig.3. A schematic view of the LEPS2 beamline

BGOegg is an egg-shaped electro-magnetic calorimeter consisting of 1320 BGO crystals of 20 radiation length, which cover a polar angle from 24 to 144 degrees and the whole azimuthal angle surrounding
the target (Fig.4). Since it has no housing material, there is no dead region between crystals. The detailsof the design and the construction of BGOegg can be found in [2, 3]. To detect charged particles, innerplastic scintillators(IPS) and a cylindrical drift chamber(CDC) are installed in front of the BGO crystals.
BGOegg can detect γ’s coming from photo-produced mesons with a high energy-resolution and a highposition-resolutions of 1.3% and 3.1 mm at 1 GeV, respectively. The resolutions are the world highest
values as an electro-magnetic calorimeter used in the energy region of 1 GeV.

§ 3. Energy calibration of BGOegg
The energy deposit for each crystal is measured by ADC information with
Ei = αi (Ai − A0i )(1)where αi , Ai , A0i are the gain factor, ADC and the pedestal value for ith crystal, respectively. Since thegain factor is different value for each crystal, these values should be determined for all 1320 channels

98

Fig.4. Left : The picture of the electro-magnetic calorimeter BGOegg. Right : Side view of thestructure of BGOegg.

by calibration. We have performed the energy calibration of BGOegg using a real data of a carbon and apolyethylene target.
3.1 Clustering
To reconstruct the particle energy and the hit position, we put some crystals in which a particle
deposits its energy together into a cluster. A cluster is defined as a set of adjacent crystals (See Fig.5).
A particle energy is reconstructed by summing up the energy deposits of all crystals in a cluster, and a
hit position is defined as an energy-weighted-mean of the positions of crystals in a cluster. When innerplastic scintillators corresponding to a cluster are fired, such events are ignored if we assume gamma
hits.

Fig.5. The definition of a cluster. In case of this figure, the cluster A consists of crystals inside
the violet line, and the cluster B consists of crystals inside the blue line. Crystals inorange have TDC information.

We can reconstruct the invariant mass of a meson decaying to γγ from energies and hit positions of
2 neutral clusters by√
Mγγ = 2EA EB (1 − cos θ)

(2)

99

where EA , EB are the energy values of the clusters, and θ is the opening angle of the clusters.
3.2 Determination of gain factors
The gain factors have been determined using π 0 → γγ events so that the π 0 peak position in the γγ
invariant mass distribution should be consistent with the π 0 mass mπ = 134.977 MeV [4]. To determine
the gain factors, we performed a successive approximation by iterating following procedures.

1, Reconstructing γγ invariant mass distribution of all combinations of 2 neutral clusters, and getting
the mean value of π 0 peak for each crystal.
2, Adjusting gain factors by the following function.
(
)
mπ
new
old
αi
= αi
mi

(3)

where αnew
, αoldare the old and new gain factor of ith crystal, respectively, and mi is the mean valueiiof π 0 peak for ith crystal obtained in 1.

These processes was iterated until convergence.
We checked the convergence with χ2 defined by
χ2 =

1320
∑(
i=1

mi − mπ
δmi

)2
(4)

where mi is the mean value of π 0 peak for ith crystal, and δmi is the error of mi . Convergence wasachieved after 15th iteration because χ2 almost stopped decreasing. After convergence, the mean valuesm (MeV)of π 0 peaks are within mπ ± 0.05 MeV for all crystals (See Fig.6).

crystal No.

Fig.6. Left : Transition of χ2 by iteration. Right : The mean values of π 0 peak after convergence.

100

3.3 Run dependence of gain factors and correlation with temperature
We checked the run dependence of gain factors. Fig.7 shows the transition of average gain factor andthe room temperature. The gain factors are stable if the room temperature is kept constant, while thecorrelation between the room temperature and the gain factors is seen when the temperature changes
significantly. The correlation can be explained by the light output of crystals and PMTs as a function of
the tempearture dL/dT ∼ −1.5 %/K.

Fig.7. Run dependence of the average gain factor(blue) and the room temperature(red). The
gain factor increases when the room temperature rises.

3.4 γγ invariant mass distribution and mass resolution
As a result of the energy calibration, the peaks corresponding to π 0 and η mesons are clearly observed in the γγ invariant mass distribution with a high mass-resollution of 6.7 MeV for π 0 , and 14.4
MeV for η. η ′ mesons are also clearly observed with a mass-resolution of 18.8 MeV. This mass-resolution
is enough to identify the η meson, and over 99% of multi-π events will be eliminated in search for η ′mesic nuclei.
The mass resolution of BGOegg is significantly high compared with other detector systems used in
the energy region of 1 GeV. Table 1 shows the comparison of the detector performance between BGOegg
and some other detectors.

101

350

38.72

/ 45
122.3
963.8
18.75
1767.
-2.7730.1086E-02

P1
P2
P3
P4
P5
P6

300

6.192
0.98571.040
14.12
0.1954E-01
0.1444E-04

counts/4MeV

250

200

150

100

50

0
800

850

900

950

1000

1050

2γ invariant mass [MeV/c2]

1100

1150

Fig.8. The γγ invariant mass distribution. Left : The overall distribution with logarithmic
scale. π 0 and η are clearly observed. Right : The distribution of events with 2 neutralclusters with linear scale. η ′ is clearly observed.

scintillator
number of crystals
energy resolution (1GeV γ)
π 0 mass-resolution σπ (MeV)(γγ invariant mass, overall)η mass-resolution ση (MeV)(γγ invariant mass, overall)

BGOegg [5]
BGO
1320
1.3%
6.7

Crystal Barrel [6]CsI(Tl)
1380
2.5%
9.9

Crystal Ball [7] [8]
NaI(Tl)
672
1.7%
10

GRAAL [9]
BGO
480
1.3%
14

14.4

16.6

22

24

Table 1. Comparison of the photon energy-resolution and the meson mass-resolution among somecalorimeters used in the energy region of 1 GeV.

3.5 More precise calibration
The energy calibration was performed to adjust the overall π 0 peak position in the γγ invariant
mass distribution to π 0 mass mπ as explained above. However, the peak position of η mesons is a little
higher than the η mass mη = 547.86 MeV [4]. In addition, the peak position of π 0 is dependent on
π 0 momenta, and shifts in the high momentum region (See Fig.9). The inconsistency of π 0 and η peak
positions is caused by an energy leakage effect. When reconstructing a cluster of a gamma hit, a few % ofenergy leaks out of the cluster. Since the ratio of energy leakage is dependent on the photon energy andthe polar angle of the hit position, a cluster energy should be corrected as a function of photon energies
and polar angles. Fig.10 shows the leaked energy ratio ∆E/E estimated by MC simulation. We checked
the leakage effect by MC simulation, and re-calibrated gain factors taking it into account.

102

Fig.9. Left : The η peak in γγ invariant mass distribution. The mean value of the peak is 555.98
MeV, which is ∼8 MeV higher than η mass. Right : The momentum dependence of theπ 0 peak position. The mean values of the π 0 peak become higher than π 0 mass as π 0momenta become large.

Fig.10. The leaked energy ratio ∆E/E as functions of photon energy(left) and the polar angleof the hit position(right) estimated by MC simulation.

Figure.11 shows the result of re-calibration. The mean value of the η peak has decreased andbecome close to the normal η mass after correction. In addition, the momentum dependence of the π 0
peak position has become almost constant.

103

Fig.11. The effect of the energy correction taking leakage into account. The red and the blue
show before and after correction, respectively. Left : The mean value of η peak is 550.40
MeV after correction becoming close to the normal η mass. Right : The π 0 peak positionis almost independent of π 0 momenta after correction.

§ 4. Timing calibration of BGOegg
Timing information of BGOegg is used for the event selection or the separation of the RF bunches of
2ns interval. To obtain the timing information independently of the crystals, we have performed timing
calibration so that the timing of a gamma hits returns 0. Since we used leading edge discriminators,
there is correlation between timing information and ADC channels due to a time-walk effect (See Fig.12).
Then we have performed a slewing correction by fitting the following function to ADC-timing correlation.
ti = t0i − αi tanh(βi (Ai − A0i )) − γ(Ai − A0i )(5)where Ai , A0i are ADC and pedestal values for ith crystal, respectively, and t0i , αi , βi are free parameters for the fit. (γ is common in all crystals.)

Fig.12. The ADC-timing correlation. The bule line in the right figure is a fitting function.

104
Figure.13 shows the timing difference distribution between 2 γ’s from the same π 0 with energies
over 200 MeV after the timing calibration. The timing difference resolution σγγ is 0.32 ns, corresponding
to the time-resolution of a single crystal of 0.23 ns. This time-resolution is enough to separate the
RF bunches, and also enough to eliminate accidental hits such as cosmic rays which is not negligible
especially in the analysis of the LH2 data.

Fig.13. The timing difference distribution of 2 γ’s from the same π 0 . Sigma of the distribution
is 0.32 ns.

§ 5. Summary
We are carrying out the LEPS2/BGOegg experiment aiming to search for η ′ mesic nuclei. A large
acceptance electro-magnetic calorimeter BGOegg is used to detect γ’s and identify mesons in final state.
We have performed energy and timing calibration with a data of a carbon and a polyethylene target. As
a result of energy calibration, the peaks corresponding to π 0 , η and η ′ mesons have been observed inthe γγ invariant mass distribution with a significantly high mass-resolutions of 6.7, 14.4 and 18.8 MeV,
respectively. As a result of timing calibration, the time-resolution of a single crystal has been achieved
to be 0.23 ns for γ’s with energies over 200 MeV, which is enough to separate the RF bunches and toeliminate accidental hits of cosmic rays.

Acknowledgment
We greatly thank the SPring-8 staff for the stabel operation of the accelerators. This work was
supported in part by Grants-in-Aid for Specially promoted Research (19002003), for Scientific Research(A) (24244022), and for Scientific Research (C) (26400287).

105

References[1]

H.Nagahiro et al., Phys. Rev. C 74, 045203 (2006)[2]

T.Ishikawa et al., ELPH Annual Report 1, Tohoku University, 61 (2012)[3]

M.Miyabe et al., ELPH Annual Report 2-4, Tohoku University, 144 (2014)[4]

Particle Data Group, Chin. Phys. C, 38, 090001 (2014)[5]

T.Ishikawa, Internal GeV-γ Analysis Note, No.231B (2011)[6]

E.Aker et al., Nucl. Instr. Meth. A321, 69 (1992)[7]

D.Watts The Crystal Ball and TAPS Detectors at the MAMI Electron Beam Facility, 11th International Conference On Calorimetry In High Energy Physics (2004)[8]

A.Thomas Recent result from the Crystal Ball Experiment at MAMI, HEPD Seminar (2010)[9]https://bgo-od.physik.uni-bonn.de/ExperimentalSetup/BgoBall

106

ELPH Annual Report, Tohoku University (2014)

Development of the liquid hydrogen target system for theelectromagnetic calorimeter BGOegg
Norihito Muramatsu1 , Takeshi Ohta2 , Masaru Yosoi2 , Yuji Ohashi3 ,Wen-Chen Chang4 , Jia-Ye Chen5 , Schin Daté3 , Hiroya Goto2 ,Hirotomo Hamano2 , Toshikazu Hashimoto6 , Qing Hua He1 , Kenneth Hicks7 ,Toshihiko Hiraiwa2 , Yuki Honda1 , Tomoaki Hotta2 , Hiroyuki Ikuno2 ,Takatsugu Ishikawa1 , Igal Jaegle8 , Yuuto Kasamatsu2 , Satoshi Kido1 ,Yukiyoshi Kon2 , Shinichi Masumoto9 , Yuji Matsumura1 , Manabu Miyabe1 ,Keigo Mizutani6 , Takashi Nakano2 , Masayuki Niiyama6 , Yuki Nozawa6 ,Haruo Ohkuma3 , Hiroaki Ohnishi10,2 , Masaya Oka2 , Kyoichiro Ozawa11 ,Takuya Shibukawa9 , Hajime Shimizu1 , Ken’ichiro Shiraishi1 ,Yorihito Sugaya2 , Shinsuke Suzuki3 , Shintaro Tanaka2 , Atsushi Tokiyasu2 ,Natsuki Tomida6 , Nam Tran2 , Yusuke Tsuchikawa1 , Hirohito Yamazaki1 ,Ryuji Yamazaki1 , and Tetsuhiko Yorita2
1

Research Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826,
Japan
2

3

Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan

Japan Synchrotron Radiation Research Institute (SPring-8), Sayo, Hyogo 679-5198, Japan
4
5

National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
67Institute of Physics, Academia Sinica, Taipei 11529, Taiwan

Department of Physics, Kyoto University, Kyoto 606-8502, Japan

Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
89University of Hawaii at Manoa, Honolulu, HI 96822, USA

Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
10

11

RIKEN Nishina Center, Wako, Saitama 351-0198, Japan

Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization(KEK), Tsukuba, Ibaraki 305-0801, JapanThe liquid target system, which is usable for hydrogen and deuterium, was developed for the
LEPS2/BGOegg experiments at SPring-8. It has a long nose with the 50 mm aperture for the beampath, in order to install the 40 mm-long target cell at the center of the electromagnetic calorimeter
BGOegg. From 2014 November to 2015 February, the liquid hydrogen target was used for the physics
data collection with the laser-backscattering photon beam, whose tagged counts reach about 3 × 1012 intotal.

107§ 1. Introduction
The LEPS2/BGOegg experiments at SPring-8 [1] has started the stable collection of physics datafrom 2014 April by using a few MHz photon beam, which is produced by the backward Compton scattering of the ultra-violet (UV) lasers and tagged in the energy range of 1.3–2.4 GeV [2]. The electromagnetic
calorimeter BGOegg surrounds a target in the polar angle region of 24◦ to 144◦ with a good energy resolution (1.3% at 1 GeV). Charged particles are identified at the inner plastic scintillators (IPS) and thecylindrical drift chamber (CDC) inside the BGOegg, as shown in Fig. 1. The forward acceptance hole iscovered by the planar drift chamber (DC, θ < 21◦ ) and the resistive plate chambers (RPC, θ < 7◦ ). The
resolution of the time-of-flight measurement at the RPC is about 80 psec, so that the proton momentum
can be calculated from the 12.5 m flight length with the resolution of ∼1% at 2 GeV/c. All of the detectors
became finally ready in June.
From April to July, we used the 20 mm-thick nuclear targets of Carbon or polyethylene (CH2 )mainly for the η 0 -mesic nuclei search. The η 0 meson acquires a distinctively large mass by the UA (1)anomaly, appearing in the QCD Lagrangian, and receives special interests compared with usual NambuGoldstone bosons. By the partial restoration of chiral symmetry breaking, the large reduction of the η 0mass by 80–150 MeV is theoretically calculated based on the Nambu-Jona-Lasinio (NJL) model [3] andthe linear sigma model [4] even at the nuclear density.
The UA (1) anomaly possibly induces an attractive interaction between the η 0 and a nucleon (“N”)
in the QCD vacuum. Therefore, the measurement of the η 0 -N scattering length is desired near the
production threshold of γp → η 0 p reaction. In addition, the η 0 possesses a large content of ss̄, whoseFig.1.

The detector setup of the LEPS2/BGOegg experiments.

108
phase relative to non-strange quark content uū + dd¯ is opposite to the case of η meson. It is expectedthat the cross sections of the η and η 0 photoproduction from a nucleon target are sensitive to the excitednucleon resonances, which strongly couple to strange quarks, along with clarifying the interferencewith the ss̄ content in the nucleon. The measurements of the beam asymmetries relative to the linear
polarization vector of photons also provide the spin information of the nucleon resonances.
The experimental data about the η 0 photoproduction from a nucleon target is still poor, and the
LEPS2/BGOegg experiments intend to measure its total and differential cross sections and photon beam
asymmetry by using a highly polarized photon beam. Such measurements of the elementary cross sections are necessarily important to understand the possible formation of the mesic nuclei, too. The experiments using the nucleon target is useful not only for the η 0 photoproduction but for various physics
opportunities, including the excited nucleon resonance searches in the s-channel of single or double meson (ω, π 0 π 0 , π 0 η, etc) photoproduction. Thus, we developed a liquid hydrogen target system, whichis also usable for a deuterium target, in parallel with the nuclear target runs. The new liquid target
system have been utilized at the physics data collection from 2014 November.

§ 2. Construction of the liquid hydrogen target system
The liquid hydrogen target system has a 1 m-long nose structure to place a 40 mm-long target
cell at the center of the large acceptance electromagnetic calorimeter BGOegg. (See Fig. 2.) The nosepart is extended from the chamber box, where the refrigerator (Sumitomo Heavy Industries, 4K GM
refrigerator RDK-408D2) is mounted on the top. The refrigerator is connected to the buffer tanks, whoseFig.2.

The side view (left) and the upstream end view (right) of the liquid hydrogen target system. The expanded side view of the target cell is also shown in the upper-left corner.

109

total volume is 300 L, by using the supply and return pipes made of Cu. The hydrogen gas is filled inside
this closed volume at ∼1.7 atm, and partially liquefied at the 98 mL reservoir under the refrigerator.
As a result of the liquefaction, the pressure of the remaining hydrogen gas becomes about 1 atm. Theliquefied hydrogen is transferred to the target cell by the self-weight while the temperature is kept at∼20 K with a heater and an automatic controller (LakeShore Model331).
The most outside of the chamber box and the φ90 nose structure is made of SUS304 to maintainthe vacuum as a thermal shield. In order to reduce the material amount around the target cell, the front
part (470 mm) of the nose is produced by a cylinder of carbon-fiber-reinforced plastic (CFRP) with the
thickness of 1 mm. Inside these vacuum containers, the whole cooling system including the refrigerator,
the reservoir, and the Cu cold finger is covered by radiation shields. The radiation shield around thetarget is also made by a 0.5 mm-thick CFRP support and Al foil. The cold finger is extended from therefrigerator inside the nose, and the cell base for the target mount is attached to the front part of the cold
finger. In order to reserve the photon beam path (σ ∼6.5 mm), those structures have enough aperture atleast with a 50 mm diameter. The front cap of the CFRP nose and the upstream wall of the SUS chamberbox also have the windows covered by 75 µm-thick polyimide films (Ube Industries, UPILEX RN). The
front faces of the CFRP nose and the Al foil radiation shield are apart from the target cell in order toachieve the better separation of the reaction products from the target and the background hits from thefront materials at their detection by the BGOegg.
The target cell is produced by gluing 125 µm-thick UPILEX films to the cell base with Stycast.
(See the upper-left part of Fig. 2.) The front cap of the cell is molded with moderate curvature, so thatthe real thickness becomes thinner to ∼50 µm. The cell volume is about 140 mL with a diameter ofFig.3.

The schematic view of the hydrogen gas flow line and the vacuum control line.

110

65 mm. The liquid hydrogen is fully filled through the lower pipe hole of the cell base, and returns to thereservoir from the upper pipe hole. For the thermal insulation of the target cell and the cooling system,
the vacuum is made inside the CFRP and SUS containers by using a turbo molecular pump and a scroll
pump, connected with the bottom of the SUS chamber box. The possible leakage of the hydrogen gas
from the cell is also exhausted by those pumps. Figure 3 shows the pipe connections for the vacuum
control and the hydrogen gas flow at the constructed target system.

§ 3. Operation at the BGOegg experiments in 2014 Nov – 2015 Feb
In 2014 October, several tests were performed for debugging the cell structure, connecting the hydrogen gas and vacuum lines without any leakage, confirming the cooling system operation with thetemperature and pressure monitors, and so on. Figure 4 shows the liquefaction status at the target cellin the view from the nose front. After the full liquefaction at the cell, the hydrogen gas pressure becomes∼1 atm at the pressure gauge, located near the buffer tanks. The liquefied hydrogen volume at the target cell, the transfer pipes, and the reservoir was calculated to be 267 mL based on the pressures before
and after the liquefaction. The temperatures at the target cell and the refrigerator head just above thereservoir were monitored by thermocouples, and the difference of the cell and head temperatures was afew K even with the nose structure.
The combination of the nose structure with the target cell and the vacuum chamber box with therefrigerator is placed on the sliding rail stage with many ball-type rollers. The nose structure wasinstalled inside the BGOegg along the guide rail, which was fixed on the large plate for enabling thetwo-dimensional position adjustment by screws. (See Fig. 5.) The stage height was also optimized by the
adjuster bolts, which were attached at the bottom of the individual stage leg and anchored to the floorof the experimental area. The target system was aligned by adjusting the cell position and the center ofthe upstream UPILEX window relative to the beam position markers. Further fine tuning was done bychecking the azimuthal hit distribution at the BGOegg calorimeter with the injection of a photon beam.
In the case of experiments with nuclear targets, this liquid target system can be slided away to the side
space off the photon beam axis, so that the experimental setup should be easily changed depending on
the physics plans.

Fig.4.

The pictures of the target cell during the hydrogen liquefaction. The liquid surface increases while the gas pressure at the buffer tanks decreases from the left picture to theright picture.

111

Fig.5.

The picture of the hydrogen target system on the sliding rail stage. The nose part isinstalled into the BGOegg calorimeter.

The whole target system was stably working from 2014 November to 2015 February at the physics
data taking. About 3 × 1012 of tagged photons were irradiated on the liquid hydrogen target in total.
In order to study the possible systematics of the detector acceptances at the measurements of spin
observables, the linear polarization vector of the photon beam was alternatively changed to the verticalor the horizontal directions. The energy and timing calibrations of individual detectors are being doneby using the collected data. The π 0 and the η mesons will be identified in the invariant mass distibutionof 2γ, which are detected at the BGOegg calorimeter. In the nuclear target data collected before the 2014
summer, those mesons have been already reconstructed with the good mass resolutions of 6.7 MeV/c2
and 14.4 MeV/c2 , respectively. The ω meson also have been successfully reconstructed from the π 0 γ
invariant mass (Br=8.3%) using the same nuclear target data. The photoproduction of the η 0 meson
will be identified by the invariant mass distributions of π 0 π 0 η (Br=21.6%) or 2γ (Br=2.2%). The 2γ
decay mode has a smaller branching fraction, but the acceptance is a few times larger and covers the η 0
production angles in more forward region. A proton in the final state of the above meson photoproduction
processes will be confirmed by the missing mass, which is calculated using the photon energy measured
at the tagging detector of a recoil electron.

§ 4. Summary
The LEPS2/BGOegg experiments have started the physics data collection from 2014 April. Firstof all we used a Carbon or CH2 target for the η 0 -mesic nuclei search, while the liquid hydrogen target
system with a 1 m-long nose structure was developed to install the 40 mm target cell inside the electro-

112

magnetic calorimeter BGOegg. A part of the hydrogen gas, stored in the large volume buffer tanks, isliquefied at ∼20 K by the refrigerator, so that the liquid hydrogen is filled at the reservoir and the target
cell. The target cell is made by 125 µm polyimide films and the material amount of the nose aroundthe cell is reduced by using CFRP cylinders. The constructed target system was installed for collecting
the γp reaction data from 2014 November to 2015 February. This data will be analyzed, for example, tomeasure the cross sections and the photon beam asymmetries in the photoproduction of η 0 , η, ω, π 0 π 0 ,π 0 η, etc for the study of nucleon resonances.

Acknowledgment
We greatly thank to the staff at SPring-8 for the support to the beamline construction and commissioning and the stable operation of the accelerators. This research was supported in part by the Ministryof Education, Science, Sports and Culture of Japan and JSPS KAKENHI Grant No. 24244022.

References[1]

N. Muramatsu, ELPH Report 2044-13 (2013) or arXiv:1307.6411.

[2]

N. Muramatsu et al., Nucl. Instr. Meth. A737 (2014) 184.

[3]

H. Nagahiro et al., Phys. Rev. C 74 (2006) 045203.

[4]

S. Sakai and D. Jido, Phys. Rev. C 88 (2013) 064906.

ELPH Annual Report, Tohoku University (2014)

113

Development of a charge-to-time (QTC) discriminator
T. Ishikawa1
1

Research Center for Electron Photon Science (ELPH), Tohoku University, Sendai 982-0826,
Japan

A charge integrating analog-to-digital converter (ADC) is too expensive only for the monitoring of
the gain and applying a pulse-height time-walk correction. In addition, a very long cable for delaying
analog signals is required for the ADC readout. It is difficult to introduce many ADC modules easily
any more by taking into account the cost of ADC modules and long delay cables. Recently, a multi-hit
time-to-digital converter (TDC) module is available, which can digitize both the timings of the leading
and trailing edges of signals. Thus, it is not necessary to use an ADC module if the output width of adiscriminator corresponds to the charge integration. The function converting the charge integration into
the width of the logic signals is called as a charge-to-time converter (QTC). We have asked Fuji DiamondInternational Co. Ltd. to produce a discriminator with a QTC function fitted to the signals for plastic
scintillators. The results of testing the developed QTC discriminator are given in this report. The QTC
discriminator has been made into a product as GeVγ-1370.

§ 1. Introduction
The ordinary ADC module integrates the charge during the gate period, and digitizes the charge
integration to give the energy deposit in a detector. The gate signal is often generated with a trigger
circuit of a data acquisition system, and is delayed in a finite time. This delay determines the lengths ofdelay cables for analog signals to match them with the gate period. Long cables with an order of µs are
required to obtain the energy deposit in scintillating fibers of STB-Tagger II at ELPH.
A flash ADC (FADC) module is a candidate to obtain the energy deposit. But A FADC chip with avery high frequency (more than several hundred MHz) is required for analog signals of plastic scintillators. We have a lot of difficulties to introduce very high frequency FADC chip:
1. high cost,
2. cooling FADC, and3. very high speed processing of digitized data
are required. On the other hand, some filter circuits are necessary when low frequency FADC chips are
adopted.
Recently, a multi-hit (MH) time-to-digital converter (TDC) module is available, which can digitize
both the timings of the leading and trailing edges of signals. The V1190 and V1290 modules of CAEN
SpA are often used MHTDC modules. Both the ADC and TDC modules are required for each signal toobtain the timing and the energy deposit. Yet, it is not necessary to use an ADC module if the output

114

width of a discriminator corresponds to the charge integration. The function converting the charge
integration into the width of the logic signals is called as a charge-to-time converter (QTC). Generally,
QTC is realized in the following way [1, 2]:
1. the input signal is amplified,
2. the charge is integrated in a capacitor,
3. The capacitor is discharged with a constant current.
Figure 1 shows the simplified circuit and charge in a capacitor.

D
Vo
C
Ii
−

Io
Vo

Vc

+

R
Id
Vd
Fig.1.

Simplified circuit and charge in a capacitor. The circuit consists of the integrator, andconstant current source Id which discharges the capacitor. The output voltage Vo of thecircuit gives a linear triangle signal.

The quiescent voltage for the capacitor C is given by the diode D. The constant current Id througha register R is defined as
Id =Vc − VdR(1)from the difference between Vc and Vd . In the idle state, all the output current Io from the operational
amplifier (OPAMP) flows through the diode D, and makes Id = Io . An input pulse makes Io smalleraccording to the current of the input signal Ii , and the charge is integrated in the capacitor C. The
circuit comes back to the idle state when the capacitor C is fully discharged by a constant current Id .
The output current of the OPAMP is
Io = Id − Ii ,(2)

and Ii = 0 in the idle state. The charge Q0 in the idle state is determined by the diode D, An input pulse
makes the charge Q in the capacitor C becomesZ
Q = Q0 − I0 (t) dt + Id t,(3)t

and output voltage becomes
Z t
Q0
1
Id
Vo = Vc +−I0 (t) dt +
t.
C
C 0
C

(4)

115

If the current Ii according to the input pulse becomes 0 in a short time as compared with the discharging
time, the behavior of Vo is expressed by the fourth term in eq. (4). A QTC discriminator should give atrue state when Vo exceeds given threshold basically.

§ 2. Developed QTC discriminator
A QTC discriminator should be desired as a high precision leading edge discriminator. Therefore,
the input signal is divided into two, and one is used for generating a leading edge of the output pulse,
and the other is input to the integrator circuit giving a linear triangle pulse. This is realized by a flip-flop
circuit so that the output signal is started by the comparator output for the former signal, and stopped
by that for the latter triangle pulse. Figure 2 shows the behavior of the QTC discriminator, and Figure 3
shows its photo.

flip-flop
input

入力

①

output

CK

VTH1

①

comparator
R②

Lin output②
amplifierintegrator
PZC

Fig.2.

Lin output

outputVTH2comparator

Behavior of the QTC discriminator. The main circuit of the QTC function described in §1
is given by an amplifier, integrator, and pole-cancellation circuit (PZC).

The VTH1 is a threshold for generating a output pulse, and VTH2 is that for determining of the widthof the pulse. The requirements for the developed QTC discriminator are
1. the leading edges with high precision according to the given threshold VTH1 , and2. the widths of the output pulses expressed by a (one polynomial) function according to the charge ofthe input signal.
The prototype QTC discriminator was produced by Fuji Diamond International Co. Ltd. to satisfy these
conditions.

§ 3. Testing the prototype QTC discriminator
We tested the prototype QTC discriminator by using the output signals of photomultiplier tube
(PMT) connected with a plastic scintillator. The plastic scintillator used was EJ-212 produced by ELJEN
Technology, and it measured 30 × 30 × 20 mm3 . It was connected to a PMT Hamamatsu H6410, and the
supplied voltage is −1100 V with a current of 279 µA. The waveform of the input and output signals of
the prototype QTC discriminator was acquired by employing a digital phosphor oscilloscope, Tektronix

116

Integration
VTH2
VTH2
GND

PZC
Lin output
NIM output
ECL output

VTH1
VTH1
GND

Fig.3.

+12 V
GND
−12V

Photo of the prototype QTC discriminator produced by Fuji Diamond International Co.
Ltd.

DPO-4104, with a sampling frequency of 5 GHz. Figure 4 shows the experimental setup for testing theprototype QTC discriminator.
EJ-212

CH1: PMT

Divider
H6410

CH2: Lin. Output
QTC
Discriminator

CH3: NIM output
MSO-4104

Fig.4.

Experimental setup for testing the prototype QTC discriminator. The input signal to
the QTC discriminator is given by the output signal of a photomultiplier tube (PMT)
Hamamatsu H6410 connected with a plastic scintillator EJ-212 with a size of 30 × 30 × 20mm3 . The waveform of the input and output signals of the prototype QTC discriminator
was acquired by employing a digital phosphor oscilloscope, Tektronix DPO-4104. The
output signal of PMT is divided into two, one is delivered to CH1 of DPO-4104, and theother is input to the QTC discriminator. The linear and NIM outputs of it is given to CH2
and CH3 of DPO-4104, respectively.

The input signal to the QTC discriminator was given by the output signal of PMT. The output signalof PMT is divided into two, one was delivered to CH1 of DPO-4104, and the other was input to the QTC
discriminator. The linear and NIM outputs of it was given to CH2 and CH3 of DPO-4104, respectively.
The waveform acquisition was made by using a library [3] developed by T. Ishikawa et al. The triggerof DPO-4104 was the falling edge of CH3 (NIM output) with a threshold of −400 mV. The measured
voltages are [−270, +30), [−100, +900), and [−1800, +200) mV for CH1, CH2, and CH3, respectively.
The waveform was recorded by 0.2 ns step with a time [−379.8, 420.0] ns. Table 1 summarizes theacquired data. To reject the accidental double pulses in the analysis, The width of the output signals of

117

PMT with a −5 mV threshold is longer than 30 ns by checking CH1 waveform. The events was rejectedthat the voltage of −270 mV was recorded in CH1. Figure 5 shows the typical waveforms for the output
signals of PMT and those of the QTC discriminator.
Table 1. Acquired data. The discriminator threshold (VTH1 ), the number of events, the effective
number of events which satisfy the conditions.
run
008
009
010
011
012

threshold−19.9 mV
−6.8 mV−45.0 mV
−60.9 mV
−31.9 mV#events
10,00010,000
3,000
3,000
3,000

#analyzed events
9,878
9,947
2,890
2,878
2,937

To obtain the amplitude V0 , timing t0 , rising time τR , and decay time τD , the functiont − t0t − t0V (t) = −V0 freq
exp −
τR
τD

(5)

is fitted to the waveform of the PMT output signal event by event. The error of each point is assumed
to be 1.12 mV, which is the resolution corresponding to the least significant bit. The fitting process wasmade with a time range [−20, −5) ns, and iterated five times with a time range [t0 − 4τR , t0 + 4τD ).
Figure 6 shows the output waveforms of PMT together with a fitted functions.
The obtained parameters are V0 = 60.6 ± 0.7 mV t = −14.76 ± 0.10 ns
0

(6)



τR = 2.34 ± 0.05 ns τD = 4.62 ± 0.10 ns
for the first event in run008, and
V0 = 324.0 ± 0.8 mV t = −11.29 ± 0.02 ns
0

(7)



τR = 2.33 ± 0.01 ns τD = 5.35 ± 0.02 ns
for the third event in the same run. The maximum pulse height Vmax is determined from the maximum
difference of the recorded pulse height in each event. The ground level VGND is also determined by theaverage pulse height in a time [−70, −30) ns. The charge integration is obtained by using a pulse height
V over a time [−30, +10) ns
Z
1Q=(V (t) − VGND ) dt =50 ΩX[−30,+10) ns

V (t)
∆t −
50 Ω

X
[−70,−30) ns

V (t)
∆t,
50 Ω

(8)

where ∆t = 0.2 ns stands for the period of the pulse height measurement. The Vmax is 38.4 and 183.6 mV,
and the charge integration Q is 6.8 and 37.5 pC for the first and third events in run008. Figure 7
shows the correlations between the charge integration Q and the amplitude V0 , that between Q and the118

File qtc000008.dat, Event: 00003

0

0

-50

-50

-100

-100

-150

PMT output-150

PMT output

400Lin. output

400Lin. output

200

0

Pulse Height (mV)

Pulse Height (mV)

File qtc000008.dat, Event: 00001

0

0

0

-500

-500

-1000

NIM output-50-25 0 25 50 75 100125150175200
Timing (ns)Fig.5.

200-1000

NIM output-50-25 0 25 50 75 100125150175200
Timing (ns)Typical waveforms for the output signals of PMT and those of the QTC discriminator.
The left panel shows the waveforms of the first event in run008, and the right one shows
those of the third event in the same run. The upper, central, and lower panels show
the waveforms of the PMT output (CH1), the linear output (CH2), and the NIM output(CH3). The green and red lines correspond to the voltage of 0 mV and the timing of 0 ns,
respectively.

maximum pulse height Vmax , and that between V0 and Vmax . All the correlation shows a proportional
function, and they give V0 /Q = 8.5 ± 0.2 mV/pC, Vmax /Q = 5.2 ± 0.2 mV/pC, Vmax /V0 = 0.61 ± 0.03 for
all the events in run008.
Since the Q, V0 and Vmax are proportional each other, the waveforms of the output signals of PMT
can be assumed to be the same. To confirm this, the rising and decay time parameters are also investigated. Figure 8 shows the rising time parameters τR and the decay time parameter τD . Both of them
are constant, all the events in run008 give τR = 2.3 ± 0.1 ns and τR = 5.2 ± 0.2 ns.
The set value of the threshold VTH1 and the effective value of the threshold Veff are investigated bylooking at the distributions of the maximum pulse height Vrmmax . Figure 9 shows the maximum pulse
height (Vrmmax ) distribution run by run. The effective threshold Veff is determined by the minimum
value of Vrmmax . The Veff is −31, −13, −65, −83, and −47 mV for run008–run012. The correlation
between VTH1 and Veff is also plotted in Fig. 9. Although VTH1 and Veff is different, Veff can be expressedby a one dimensional polynomial function of VTH1 . Taking the error of Veff to be 1 mV, VTH1 is expressedPulse Height (mV)

Pulse Height (mV)

119

0
-100

0
-100

-500

Pulse Height (mV)

Pulse Height (mV)

-30

-20

Event: 00003
-1000
-10
0
10
Timing (ns)0 10 20 30 40 50 60
Q (pC)

Fig.7.

0

Event: 00001
100
200
Timing (ns)0

Event: 00003
100
200
Timing (ns)

400
300
200
100
0

Vmax (mV)

Typical waveforms of PMT output signals (left) and those of NIM output signals of the
QTC discriminator. The upper panels show the waveforms for the first event in run008,
and the lower show those for the third event in the same run. The green lines stand forthe voltage of 0 mV, and the red curves show the fitted functions expressed in eq. (5) and(10).

Vmax (mV)

V0 (mV)

400
300
200
100
0

-500

Event: 00001
-1000
-20
-10
0
10
Timing (ns)0-30

Fig.6.

0

0 10 20 30 40 50 60
Q (pC)

400
300
200
100
0

10 3
10 2
10
0

1

100 200 300 400
V0 (mV)

Correlations between the charge integration Q and the amplitude V0 (left), that between
Q and the maximum pulse height Vmax (central), and that between V0 and Vmax (right).
The correlations are given by the events in run008.

as a function of Veff(−Veff ) = (4.3 ± 0.9) + (1.327 ± 0.024) (−VTH1 ) .

(9)

A function
V (t) = Vc − Va freqt − tlτl
1 − freqt − ttτt(10)is fitted to the NIM output of the QTC discriminator to obtain the ground level Vc , the amplitude Va , theleading edge timing tl , the rising time of the leading edge τl , the trailing edge timing tt , and the falling
time of the trailing edge τt event by event. The error of each point is assumed to be 7.81 mV, which is theresolution corresponding to the least significant bit. The fitting process was made five times with a time
range [−30, +270) ns. Figure 6 shows the waveform of the NIM output signals of the QTC discriminator

120Counts / 0.05 ns

Counts / 0.05 ns

3000
1000

2000
1000
0

Fig.8.

0

0.5

1

1.5

2 2.5
τR (ns)

3

3.5

4

500

0

0

1

2

3

4
5
τD (ns)67

8

Rising time parameter τR (left) and decay time parameter τD (right). These parameters
are given by the events in run008.

for the first and third events in run008. The obtained parameters are
Vc = 5.3 ± 0.2 mV





 Va = 906.6 ± 0.8 mV t = 0.14 ± 0.00 nsl τl = 0.21 ± 0.00 ns






tt = 23.62 ± 0.00 ns τt = 0.26 ± 0.00 ns
for the first event in run008, and
Vc = 6.8 ± 0.2 mV





 Va = 902.3 ± 0.4 mV t = 0.30 ± 0.00 nsl τl = 0.20 ± 0.00 ns






tt = 89.39 ± 0.00 ns τt = 0.26 ± 0.01 ns

(11)

(12)

for the third event in run008. The width of the NIM output signal tW is determined by the time difference
between the leading and trailing edges event by event. The width is 23.49 and 89.09 ns for the first andthird events in run008, and becomes longer as the charge integration larger.
To confirm that the NIM output is stable. th ground level Vc , the amplitude Va , the rising timeof the leading edge τl , and the falling time of the trailing edge τt are investigated. Figure 10 shows
the distributions for the ground level Vc , the amplitude Va , the rising time of the leading edge τl andthe falling time of the trailing edge τt . All the variables are constant, and Vc = 6.0 ± 0.7 mV, Va =905.9 ± 2.4 mV, τl = 0.18 ± 0.05 ns, and τt = 0.27 ± 0.02 ns in run008. The τl and τt is approximately
the same value of the sampling period of DPO-4104 (0.2 ns), which indicate the transition time of thestates is very short.
The correlation between the charge integration Q and the width of the NIM output signals tw isinvestigated run by run. Figure 11 shows the correlation between Q and tW . The tW is proportional to
Q for all the runs. The very small threshold deteriorates the linearity between Q and tW at very close-83 mV (set -60 mV)
80 qtc000011.dat
60
40
20
0
0
50 100 150 200
Vmax

Counts / 2 mV

500
0

Fig.9.

050Counts / 2 mV

-65 mV (set -45 mV)
100 qtc000010.dat
75
50
25
0
0
50 100 150 200
Vmax

1000

Veff (mV)

100 150 200
Vmax-31 mV (set -20 mV)1000 qtc000008.dat
750
500
250
0
0
50 100 150 200
Vmax

Counts / 2 mV

-13 mV (set -7 mV)
qtc000009.dat

Counts / 2 mVCounts / 2 mV

121

-47 mV (set -32 mV)
100 qtc000012.dat
75
50
25
0
0
50 100 150 200
Vmax
100
80
60
40
20
0

0

20 40 60 80 100
VTH1 (mV)Maximum pulse height (Vmax ) distributions for the runs, and the correlation between
the set value of the threshold VTH1 and the effective value of the threshold Veff . The
panels show the Vmax distributions for run009, run008, run012, run010, and run011 fromthe upper left. The green lines show Veff . The VTH1 and Veff are described in each panel.
The lower right panel shows the correlation between VTH1 and Veff . The absolute value isadopted for these values.

to the threshold (run009). The tW is fitted by a function of Q expressedtW (Q) = CW Q + t0W ,(13)

and the charge to time conversion factor CW and the minimum width corresponding to the charge
integration of 0. The obtained parameters are
(10.72 ns, 2.10 ns/pC)






 (7.95 ns, 2.15 ns/pC) 
0tW , CW =(7.50 ns, 2.15 ns/pC)





(7.57 ns, 2.14 ns/pC) (7.85 ns, 2.12 ns/pC)

for Veff = −13 mV (run09),
for Veff = −31 mV (run08),
for Veff = −47 mV (run12),(14)

for Veff = −65 mV (run10), andfor Veff = −83 mV (run11).

The t0W is a little bit large, and CW is a little bit small for the run with a very small threshold (run008).
Except for this run, both the CW and t0W parameters are constant independently of the given threshold
VTH1 .
The correlation between the charge integration Q and the leading edge timing of the NIM outputof the QTC discriminator tL are investigated. The leading edge timing of the NIM output of the QTC
discriminator tL is determined by tl − t0 , where tl and t0 is the timings for the PMT and NIM output
signals measured by DPO-4104. Figure 12 shows the correlation between Q and tL . The correlation issimilar to the ordinary leading edge discriminator. This is because the leading edge is determined only
by a comparator. Since the tW is a one dimensional polynomial function of Q, and t0 can be given fromtL by using tW .

122
4000
Counts / 0.5 mVCounts / 0.5 mV

1000

3000
2000
1000
0

-20

-10

0
10
Vc (mV)

750
500
250
0
880

20

890

900 910Va (mV)

920

930

0.2

0.4
0.6
τt (ns)0.8

1Counts / 0.01 ns

Counts / 0.01 ns

6000
4000

4000

2000

2000
0

Fig.10.

0

0.2

0.4
0.6
τl (ns)

0.8

1

0

0

Distributions for the ground level Vc (upper left), the amplitude Va (upper right), therising time of the leading edge τl (lower left), and the falling time of the trailing edge τt(lower right) for the NIM output of the QTC discriminator. All the values are determinedby the events in run008.

The details of the analysis for testing the prototype QTC discriminator are described elsewhere [4].
A slight problem on the difference between set and effective threshold values has been fixed, and a QTC
discriminator has been made into a product as GeVγ-1370. GeVγ-1370 will be tested by using a time offlight measurement of the positron beam.

§ 4. Summary
A discriminator with a charge-to-time converter (QTC) has been designed, which converts the
charge integration into the width of the output logic signals. The prototype QTC discriminator was
manufactured by Fuji Diamond International Co. Ltd. The leading edge timing of the output logic signals given by the discriminator is similar to the ordinary leading edge one. The width of the output
signals is expressed by a one dimensional polynomial function of the charge integration. This discriminator together with a multihit TDC is very useful for both the measurements of the timing and theenergy deposit. A slight problem has been fixed, and a QTC discriminator has been made into a productas GeVγ-1370.

Acknowledgement
The author thanks Mr. Yasuo Takeda, and Mr. Toshimitsu Takeda in Fuji Diamond International
Co. Ltd. for accepting the cooperation of the development of the QTC discriminator. This work was
supported in part by Grant-in-Aids for Scientific Research (A) (24244022) and for Scientific Research (C)

123

10 3

100

100

100

10 2

50

10

0
0 10 20 30 40 50 60
Q (pC)150

50

tW (ns)150 -47 mV (set -32 mV)
qtc000012.dattW (ns)150 -31 mV (set -20 mV)
qtc000008.dat

tW (ns)150 -13 mV (set -7 mV)
qtc000009.dat

00
0 10 20 30 40 50 60
0 10 20 30 40 50 60
Q (pC)Q (pC)
-65
mV
(set
-45
mV)
-83
mV
(set -60 mV)
150
150
qtc000010.dat
qtc000011.dat
100tW (ns)50
00 10 20 30 40 50 60
Q (pC)

0
0 10 20 30 40 50 60
Q (pC)

Correlation between the charge integration Q and the width of the NIM output signals
tw . The panels show the correlation between Q and tW for run009, run008, run012,
run010, and run011 from the upper left. The VTH1 and Veff are described in each panel.
The lower right panel shows the correlation between VTH1 and Veff . The tW is proportional to Q for all the runs. The very small threshold deteriorates the linearity between
Q and tW at very close to the threshold (run008).

tL (ns)20 -13 mV (set -7 mV)
qtc000009.dat
17.5
15
12.5
10

20 -31 mV (set -20 mV)
qtc000008.dat
17.5
15
12.5
10

tL (ns)Fig.11.

50

0 10 20 30 40 50 60
Q (pC)

10 3
10 2
10
1

tL (ns)0 10 20 30 40 50 60
0 10 20 30 40 50 60
Q (pC)Q (pC)
20 -65 mV (set -45 mV)
20 -83 mV (set -60 mV)
qtc000010.dat
qtc000011.dat
17.5
17.5
15
15
12.5
12.5
10
10

tL (ns)20 -47 mV (set -32 mV)
qtc000012.dat
17.5
15
12.5
10

tL (ns)tW (ns)100

0 10 20 30 40 50 60
Q (pC)
Fig.12.

0 10 20 30 40 50 60
Q (pC)

Correlation between the charge integration Q and the leading edge timing of the NIM
output signals tL . The panels show the correlation between Q and t+ for run009, run008,
run012, run010, and run011 from the upper left. The VTH1 and Veff are described in eachpanel.

124(26400287).

References[1]

C. Parl et al.: Fast Charge to Pulse Width Converter for Monolith PET Detector, IEEE Trans. on
Nucl. Sci. 59, 1809 (2012).

[2]

Y. Lin: Application of the Charge to Time Conversion Technique in Radiation Spectroscopy,
Progress in Nuclear Science and Technology 1, 206 (2011).

[3]

T. Ishikawa: Internal GeV-γ Analysis Note No. 151A (2009);
T. Ishikawa: Internal GeV-γ Analysis Note No. 177A (2010).

[4]

T. Ishikawa: Internal GeV-γ Analysis Note No. 356C (2014).

ELPH Annual Report, Tohoku University (2014)

125

Commissioning of the Electron spectrometer for the SCRIT
electron scattering facility
K. Tsukada1 , A. Enokizono3 , K. Kurita3 , S. Matsuo3 , Y. Moriya1 , T. Ohnishi2 ,T. Suda1 , T. Tamae1 , M. Togasaki3 , T. Tsuru1 , R. Toba4 , K. Yamada3 ,S. Yoneyama1 , and M. Wakasugi2
1

Research Center for Electron Photon Science, Tohoku University, Sendai, 982-0826
2

RIKEN Nishina Center for Accelerator-Based Science, Wako, 351-0198
34Department of Physics, Rokkyo University, Tokyo, 171-8501

Department of Electrical Engineering, Nagaoka University of Technology, Niigata, 940-2137

We have developed the SCRIT electron scattering facility to realize electron scattering experiments
off unstable nuclei. In December 2014, a commissioning experiment was carried out using a tungsten
wire target just after the construction of an electron spectrometer and new luminosity monitor systemcompleted. The elastically scattered electrons were successfully identified with the electron spectrometer. The present status of analysis are reported here.

§ 1. Introduction
Electron scattering provides the most powerful and reliable information of the nuclear structure.
Many stable nuclei have been investigated and our understanding of nuclear structures have been established by electron scattering experiments in the latter half of the 20th century after the Nobel-prize
experiments by R. Hofstadter and his colleagues [1]. This method, however, could be applied almost only
stable nuclei because of the difficulty to prepare the target material for unstable nuclei. Now, it is revealed that some of nuclei far from stability have exotic structures such as halo, skin, magicity loss, andnew magic numbers, and many scientific efforts for understanding unstable nuclear structures are being
made over the world. Because of the great advantages of electron scattering for the nuclear structurestudies, actualization of electron scattering off unstable nuclei has been awaited.
Under these circumstances, we proposed a completely new target-forming technique, namely SCRIT(Self-Confining Radioactive isotope Ion Target) which makes electron elastic scattering off unstable nuclei possible [2]. After the success of the feasibility study of the SCRIT system [3, 4], we have developped
the SCRIT electron scattering facility at RIKEN RI Beam Factory, Japan. In 2011 and 2012, a series ofexperiments has been performed, and the minimum required luminosity for elastic scattering, ∼ 1027[/cm2 /s], was proved with using stable nuclei, 133 Cs and 132 Xe [5].
To realize electron scattering off unstable nuclei, a high resolution and wide acceptance electron
spectrometer have also been developped. In this report, the first measurement of electron scatteringwith the electron spectrometer is reported.

126§ 2. Experimental apparatus
2.1 overview of the facility
The facility consists of a 150-MeV injector racetrack microtron, an ISOL system, 700-MeV electron
storage ring equipped with the SCRIT system, and the electron spectrometer. The electron beam energy
can be controlled from 100 MeV to 700 MeV. The current of the stored electron beam is currently 350 mA
at the maximum. Details of the electron accelerators and ISOL system can be found elsewhere [5, 6].
2.2 Electron spectrometer (WiSES)The electron spectrometer (WiSES:Window-frame Spectrometer for Electron Scattering) consistsof a dipole magnet [7], FDC (Front Drift Chamber), RDC (Rear Drift Chamber), plastic scintillator hodoscope, and a helium bag. Figure 1 shows a schematic view of WiSES and the SCRIT system.
The geometrical parameters and materials of the drift chambers are listed in Table1 and 2. Byusing FDC and RDC, we can reconstruct trajectories of scattered electrons in the magnetic field andestimate their momenta. Our goal of momentum resolution is δp/p ∼ 1×10−3 for 300 MeV electron. The
plastic scintillator hodoscope generates trigger signals. The solid angle of the spectrometer is evaluatedto be about 80 msr by GEANT4 simulation. In order to reduce the multiple scattering of electrons, aberyllium plate of thickness 2 mm is used as the SCRIT chamber window, and the helium bag made ofvinyl sheets of thickness 30 µm is installed between FDC and RDC.

Fig.1.

Schematic view of WiSES. A window of the SCRIT chamber is made of the beryllium plateof thickness 2 mm. The space between FDC and RDC was filled with helium. A trajectory
between FDC and RDC was reconstructed by a Runge-Kutta calculation.

Figure 2 shows an acceptance map of WiSES which covers a wide angular region, 30< θ <55 [deg.]and -10< φ <10 [deg.]. At the forward region, especially, the vertical acceptance become large because

127

of a vertical focusing by the magnetic fringe field.
Table 1. Geometrical parameters of FDC and RDC.
#readout
1002
128

RDC
FDC

Cell typehoneycomb
honeycomb

Table 2. Materials of FDC and RDC.
Window
Gas
Sense wire
Al-mylar 25µm He+CH4 (50:50) Au-W 30µmφ
Al-mylar 20µm He+CH4 (50:50) Au-W 30µmφ

Azimuthal Angle [deg]

RDC
FDC

Layer configuration
UU’VV’XX’UU’VV’
XX’XX’

Cell size
10 [mm]
18 [mm]Field (Shield) Wire
Au-Al 80µmφ
Au-BeCu 100µmφ

15
10
5
0
-5

-10
-15
25

30

35

40

45

50

55

60

Polar Angle [deg]Fig.2.

Acceptance map of WiSES evaluated by a GEANT4 simulation. It is assumed that electrons are scattered at the center of the SCRIT system. Because of the vertical focusing
due to the fringe field at the entrance and exit of the magnet, the vertical acceptancebecome large in the forward region.

§ 3. Commissioning run
In December 2014, a commissioning experiment was performed to evaluate the perfomance of
WiSES. Metal wires of diameter 50 µm made of tungsten and titanium were separately mounted asstable nuclear targets in the SCRIT chamber, and their position could be remotely controlled. Because
their differential cross sections for elastic scattering are known, the perfomance of the spectrometer
could be evaluated by checking the reproducibility of the differential cross sections. Figure 3 shows theinside of the SCRIT chamber.
The titanium wire was, unfortunately, found to be broken after the chamber baking, so the experiment was done with only the tungsten wire. The stored electron beam energy of 150 MeV was mainly
used because the differential cross section has an inflection point in the acceptance region and reasonable magnitude for that beam energy. The differential cross section calculated by DREPHA code [8]which is a DWBA calculation is shown in Fig. 4.

128

10-22
10-23

184

W target
Ee=100 MeV
Ee=150 MeV

10-25

Ee=300 MeV

10-27
10-29
10-3120dσ [cm2/Sr]dΩ

A picture of the SCRIT chamber’s inside. The beryllium window was removed to replace
the SCRIT electrode. The electron beam goes through the SCRIT system, and scatteredby nuclear ions trapped along the beam line. During the commissioning experiments, thetungsten wire attached on the fork was used as a stable nuclear target.

dσ [cm2/Sr]dΩFig.3.

10-22
10-23

W target
Ee=100 MeV
Ee=150 MeV

10-25

Ee=300 MeV

10-27
10-29

30

40

50

60

10-31

Polar angle [deg]Fig.4.

184

0.5

1

1.5

Momentum transfer [fm-1]

The differential cross sections for 184 W target calculated by DREPHA code. Left figure
shows the angular dependence, and right one the momentum transfer dependence.

§ 4. Data analysis
Because RDC has tilted wires, the electron tracks can be three-dimensionally reconstructed. On
the other hand, because FDC has only vertical wires, only horizontal information is available. Note thatthe time origin for FDC must be calculated using the flight length information between FDC and RDC
since the trigger counter defining the timing was set beyond RDC.
The most probable trajectory between FDC and RDC is derived by the MINUIT program includedin cern ROOT library. The position and direction differences from reconstructed tracks at RDC (δxRDC ,0δx0RDC , δyRDC , δyRDC) and a momentum difference from that of the electron beam, δp/p, are used asparameters. Then, the position and direction difference at FDC (δxF DC , δx0F DC ) can be calculated by

129
the 4th Runge-Kutta method. In the MINUIT, the following χ2 is minimized,

!2 
!2

2
2
0
0
δx
δx
δy
δy
1
RDC
RDC
RDC
RDC

+
+
+
χ2 =
0
N −1
σxRDC
σx0RDC
σyRDC
σyRDC

+

δxF DCσxF DC

2+

δx0F DC
σx0F DC!2 
.

In present analysis, the magnetic field calculated by a finite element method, OPERA-3D, is used, andthe magnitude of the field is scaled with the measured value by an NMR. After the minimization, themomentum of trajectory is defined, and the vertex point and direction on the beam line are derived
from position and direction at FDC. Figure 5 shows the vertex point distributions. A peak at the centeris corresponding to the tungsten wire, and one beside the target is a shadow of one side of the fork
fixing the wire. Because the fork is located off the beam axis and the vertex points are reconstructedwith an oblique angle, the shadow is projected upstream target. Two peaks at VZ = ±400 [mm] arecorresponding to entrance and exit electrodes of the SCRIT system. Structures at VY = ±25 [mm] arealso the parts of the SCRIT system. The vertical and horizontal resolutions are evaluated to be 7.1 [mm]and 11.5 [mm] in σ, respectively.

Vy [mm]

100

100

(a)

beam direction

100(b) -35<Vz<35(c) 100<Vz<300

Fork

50

50

50

σy= 7.1mm
0

0

0

-50

-50

-50

-100

-100

Tungsten
-100

103

-400

-200

0

200

400

(d) -5.0<Vy<5.0
σz=11.5mm

102
10
1
103

-400

-200

0

200

-400

-200

0

200

(e) -100<Vy<100

400

102
10
1

Fig.5.

400

Vz [mm](a) Vertex point distribution reconstructed by FDC and RDC for the 150-MeV data set. A
clear enhancement at the center corresponds to the tungsten target. A peak beside target
is shadow of the fork fixing tungsten wire. Other structures correspond to the SCRIT
electrodes. (b) A projection onto Vy within −35 < V z < 35 [mm]. Vertical resolution
is evaluated to be 7.1 [mm]. (c) A projection onto Vy within 100 < V z < 300 [mm].
Black blocks represent materials position of the SCRIT electrode. (d) A projection onto
Vz within −5 < V y < 5 [mm]. Horizontal resolution is evaluated to be 11.5 [mm]. (e) A
projection onto Vz within −100 < V y < 100 [mm].

130

Figure 6 shows a reconstructed momentum distribution with the vertex point cuts, -35<Vz<35[mm] and -21<Vy<21 [mm]. A clear peak corresponding to the elastic scattering can be seen. Low
momentum tail in Fig. 6 can be roughly explained by considering the effects of radiation (radiative tail)at the reaction and the energy deposit at the beryllium window. Figure 7 shows angular dependence ofthe momentum distributions. Black line shows the experimental results, and red one the simulation. In
the simulation, the angular distribution was calculated by DREPHA code [8], and the radiative tail is
included [9] in a particle generator of the simulation.
Although each simulation data is scaled by the number of events in Fig. 7, those scaling factors areslightly different each other so far. This is due to a lack of knowledge of geometries of the spectrometerand the magnetic field map. We need more study to decide the acceptance.

Ee = 150 MeV
χ2FDC<10 & χ2RDC<10

10000|Vz|<35 mm|Vy|<21 mm

5000

0
100

110

120

130

140

150

160

Momentum [MeV/c]
Fig.6.

Reconstructed momentum distribution.
21<Vy<21 [mm], are applied.

Vertex point cuts, -35<Vz<35 [mm] and -§ 5. Conclusions and future prospects
The SCRIT electron facility will realize electron scattering off unstable nuclei for the first time. The
primary goal for this facility is to determine their charge density distributions by elastic electron scattering. Construction of the electron spectrometer, WiSES, completed and the commissioning experimentwith a tungsten wire target was carried out in December 2014. The elastically scattered electrons weresuccessfully identified, and the momentum distributions can be roughly explained by the simulation
taking into account the angular distribution by the DWBA calculation and the radiative tail.
Because the target ion transport line from the ISOL system will be ready soon, the electron scattering experiment with series of the Xe isotopes and 132 Sn trapped by the SCRIT system will be performed
this year.

Acknowledgment
This work is supported by Grants-in-Aid for Scientific Research (S) (Grands No. 22224004) from
JSPS.

131

104

30.5<θ<31.5

103

31.5<θ<32.5

32.5<θ<33.5

33.5<θ<34.5

34.5<θ<35.5

35.5<θ<36.5

102

103

120

140

160
100

36.5<θ<37.5

120

140

100
160

37.5<θ<38.5

120

140

1

1

100
160

38.5<θ<39.5

10

10

1

1

1

1
100

10

10

10

10

120

140

160
100

39.5<θ<40.5

120

140

160
100

40.5<θ<41.5

120

140

160

140

160

140

160

120

140

160

120

140

160

41.5<θ<42.5

102

10

10

10

10

10

1

1

1

1

1

10

1

3

10100

120

140

160
100

120

140

120

140

160
100

140

100
160

120

140

160
100

120

140

160
100

45.5<θ<46.5

120

47.5<θ<48.5

46.5<θ<47.5
10

10

10
10

120

140

100
160

1

1

1

1

1
100

120

44.5<θ<45.5

10

10

100
160

43.5<θ<44.5

42.5<θ<43.5

102

120

140

1
100
160

120

140

160
100

120

140

160
100

120

102

48.5<θ<49.5

49.5<θ<50.5

51.5<θ<52.5

50.5<θ<51.5

10

120

140

160
100

120

140

55.5<θ<56.5

54.5<θ<55.5

10

100
160

120

140

1

10

-1

1

1

1

1

1
100

10

10

10

10

10

52.5<θ<53.5

56.5<θ<57.5

100
160

120

140

160
100

1
120

140

160
100

10

10

10

1

1

1

-1

-2

-1

-1

-3

-2

-2

53.5<θ<54.5

1
1
100

Fig.7.

120

140

100
160

120

140

160
100

120

140

100
160

120

140

160
100

120

140

100
160

Angular dependence of the momentum distributions. Black histogram shows the experimental results. Red histogram shows the simulation taking into account the radiative
tail and the energy deposit at the beryllium window. Each simulation is scaled by thesurface of histogram.

References[1]

B. Hahn, D. G. Ravenhall and R. Hofstadter: Phys. Rev. 101 (1956) 1131.

[2]

M. Wakasugi et al.: Nucl. Instr. and Meth. A 532 (2004) 216.

[3]

M. Wakasugi et al.: Phys. Rev. Lett. 100 (2008) 164801.

[4]

T. Suda et al.: Phys. Rev. Lett. 102 (2009) 102501.

[5]T. Suda et al.: ELPH Annual Report 2011-2013 Vol. 2, Tohoku University, 201 (2013).

[6]

T. Ohnishi et al.: Nucl. Instr. and Meth. B 317 (2013) 357.

[7]

T. Tamae et al.: ELPH Annual Report 2011-2013 Vol. 2, Tohoku University, 1 (2013).

[8]

B. Drepher, DREPHA: a phase-shift calculation code for elastic electron scattering, communicatedby J. Friedrich.

[9]J. Friedrich: Nucl. Instr. Meth. 129 (1975) 505.

132

ELPH Annual Report, Tohoku University (2014)(ELPH Experiment : #2775)

Radiochemical Determination of Photonuclear Reaction
Yields for Photon Activation Analysis
Yasuji Oura1 , Yuki Yamaguchi1 , and Yoshihisa Tanaka1
1

Department of Chemistry, Tokyo Metropolitan University, Hachioji, 192-0397

Relative reaction yields of (γ, n) reaction induced by bremsstrahlung of maximum end-point energyof 30 MeV and 20 MeV were reported for the target nuclides with mass number from 12 to 204. Relative
yields were systematically increased with an increase of target mass number. With this correlation, any
yield ratio is roughly able to be estimated.

§ 1. Introduction
We have been determining yields of photo nuclear reaction, especially (γ, n) reaction, to be valuablefor photon activation analysis (PAA) because of a lack of useful data set of yields of (γ, n) and (γ, pxn)
reactions induced by bremsstrahlung, which are used for an elemental analysis by PAA. Segebade etal. published a textbook on photon activation analysis in 1988 [1], in which induced radioactivity ratios
normalized with radioactivity of 57 Ni produced by 58 Ni(γ, n) reaction are listed. As far as we know, thislist is an only useful data set for PAA.
Our measurement was started at first with bremsstrahlung from an electron linac at Kyoto University Research Reactor Institute and yields of photo nuclear reaction producing radionuclides with along half life ( > 8 hours) were determined [2, 3]. In FY2013 yields of photo nuclear reaction producing
radionuclides with a short half life ( < 8 hours) as well as a longer half life for target nuclides with ≥35 of mass number were determined by using a linac at Research Center for Electron Photon Science(ELPH), Tohoku University.
In FY2014 we continuously determined photo nuclear reaction yields at ELPH and a main objectivein this study was that yields for target nuclides with < 40 of mass number was determined.

§ 2. Experimental
About 50 to 100 mg of high purity powder reagents such as C, KF, NaCl, Sc2 O3 , Cr, Fe2 O3 , Mn, Co,
Cu, ZnO, Ga2 O3 , SrCl2 , Y2 O3 , ZrO2 , Mo, CdO, Na2 H4 TeO6 , KI, CsCl, Yb2 O3 , and PbO2 were wrapped inaluminum foil to be formed a disk (10 mmφ) shape. For Au target and Ni monitor, 10 mmφ of Au foil
(0.01 mm thick) and 10 mmφ of Ni foil (0.04 mm thick) were used, respectively.
The targets together with Ni monitors in a quartz tube were irradiated for 5 min and 10 min withbremsstrahlung beam of maximum end-point energy (E0 ) of 30 and 20 MeV, respectively. After irradiation, target disks were subjected to gamma-ray spectrometry by a Ge detector. To reduce true coincidence

133effect, a sample was placed at about 20 cm far from a detector. Since the bremsstrahlung beam flux was
not determined, reaction yields normalized with one of 58 Ni(γ, n)57 Ni were calculated.

§ 3. Results and discussion
Target mass yield ratios of (γ, n) reactions for E0 = 30 MeV and 20 MeV studied at ELPH are shownin Fig.1 1 together with data obtained in experiment #2757. (Some data obtained in experiment #2757
were made corrections.) Yield ratios of reactions producing meta-stable nuclides are shown separately by
open circles. Yield ratios (58 Ni ≡ 1 ) shown by solid circles generally increase smoothly with increasing
target mass number from 12 C to 204 Pb both for E0 = 30 and 20 MeV, although some yield ratios arescattered. On the contrary, yield ratios of reactions producing meta-stable nuclides shown by open
circles are smaller than systematic yield ratios for ground state nuclides.

Fig.1.

Target mass yield for (γ, n) reactions at E0 = 30 MeV and 20 MeV. Relative yield values
normalized with a yield of 58 Ni(γ, n)57 Ni are shown. Open circles show yield ratios ofreaction producing a meta-stable nuclides

Yield ratios at E0 = 20 MeV were roughly consistent with those at E0 = 30 MeV except for sometarget nuclides. The yield ratio of 12 C(γ, n)11 C at E0 = 20 MeV was about 10 times smaller than one
at E0 = 30 MeV. A high threshold energy (18.7 MeV) of 12 C(γ, n)11 C probably results in this low ratio
observed at E0 = 20 MeV, because bremsstrahlung with E0 = 20 MeV have little photons inducing 12 C(γ,n)11 C reaction. Yield ratio of 39 K(γ, n)38 K at E0 = 20 MeV was also about 10 times smaller than anestimated systematic yield. Since yield ratio of 39 K(γ, n)38 K at E0 = 30 MeV was not determined yet, weshould determine a yield ratio at E0 = 30 MeV to confirm that the deviation for 39 K at E0 = 20 MeV iscaused by a difference of irradiation energy.
Specific radioactivity of 57 Ni induced by 58 Ni(γ, n) reaction for 1 hour at E0 = 30 MeV and 20 MeV
were about 48 kBq/mgNi and 6 kBq/mgNi, respectively. Using these specific radioactivity and induced
radioactivity ratio values compiled by Segebade et al. [1], we can estimate radioactivity produced by (γ,134n) reaction at ELPH.
Although observed values at less than 50 of a target mass number are not enough, the systematic
correlation between relative reaction yield ratio and mass number observed in this study can help an
estimation of (γ, n) reaction yield ratios for various elements. We are going forward to determine yieldratios especially at less than 50 and apply yield ratios to photon activation analysis using an internal
standard method.

Acknowledgment
The authors are indebted to Dr. H. Kikunaga and the accelerator operating crew members of Tohoku
University for their invaluable cooperation in irradiation of samples and/or accelerator operation.

References[1]

C. Segebade et al.: Photon Activation Analysis, Walter de Gruyter (1988).

[2]

Y. Oura et al.: CO2-1 in KURRI Progress Report 2012 (2013).

[3]

Y. Oura et al.: CO5-5 in KURRI Progress Report 2013 (2014).

ELPH Annual Report, Tohoku University (2014)135(ELPH Experiment : #2785)

Study on Metallofullerene Encapsulating Artificial Radio
Element of Promethium
K. Akiyama and S. Miyauchi
Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1
Minami-Ohsawa, Hachioji, Tokyo 192-0397
The metallofullerenes encapsulating artificial radio element of Promethium (Pm) was studied.
Promethium isotopes were produced from natural Sm by the photon irradiation at Research Center
for Electron Photon Science, Tohoku University. The highest productivity of produced Pm isotopes wasfound to be that of 143 Pm. Promethium metallofullerene was produced by an arc discharge method. The
valence state of Pm in the metallofullerene was strongly suggested to be trivalent from the similarity of
HPLC elution behavior for Pm metallofullerenes with those for trivalent metallofullerenes.

§ 1. Introduction
Endohedral metallofullerenes (EMFs) are known as a clathrate compound and are attracting interest of the expectation for the potential application brought from their unique physical and chemical
properties. The large number of studies about the EMFs have been reported, so far. Especially for the
EMFs of lanthanide, it has been studied for a variety of encapsulated elements from the dawn of metallofullerene research. However, only metallofullerene of promethium (Pm) has been still missing [1]. It
is well known that Pm is one of the artificial elements belonging to lanthanide elements and do not haveany naturally occurred stable isotope. The chemical property of Pm is considered to be almost same as
those of other neighboring lanthanides, actually most stable oxidation state in water is +3 similar toneighboring element of Nd. In general, Pm is produced from processing nuclear fuel and neutron irradiation of Nd in High Flux Isotope Reactor. However, 147 Pm produced by these methods is not suitable
for the metallofullerene research because of their small γ-ray emission rate and their long half life.
Some of lanthanide elements in fullerene cage are reduced by the electron rich environment offullerene inside. Actually, the valence state of Sm, Eu, Tm, and Yb in fullerenes is divalent even thoughmost stable valence state of these elements in the air is trivalent [1]. Pm is located between Nd and
Sm on the periodic table. Considering about the chemical properties of Pm as mentioned above, it isvery important to investigate the valence state of Pm in fullerene cage from the view point of lanthanide
chemistry. In this paper, we report the synthesis of Pm metallofullerene and their properties observed
from elution behavior on the high performance liquid chromatography (HPLC).

136§ 2. Experimental
2.1 Production of promethisum
To investigate the optimal condition for the irradiation and the produced radio activity of each Pm
isotope from natural Sm isotopes by (γ, n) and (γ, p) reaction with bremsstrahlung converted fromelectron beam, we employed nat Sm oxide for the production of Pm. About 0.1 g of Sm oxide was sealed
into quartz tube under reduced pressure. Photon irradiation of the samples was performed at ResearchCenter for Electron Photon Science, Tohoku University with the beam energy of 20, 30, 40, and 50 MeV
for 0.5 hours.
2.2 Pm Metallofullerene production
Irradiated Sm oxide was dissolved into concentrated nitric acid and 147 Nd radio tracer was added inthis solution for the comparison. This solution was heat to dryness and then EtOH was added to dissolve
resultant nitrate salts. This EtOH solution was dropped on a porous carbon rod with 10 mm diametersand 60 mm length to adsorb the nitrate salts and then dried. This porous carbon rod was placed in anelectric tubular furnace and sintered at 700 o C under N2 gas flow. After the sintering, this rod was set
into the fullerene generator as an anode for the arc discharge. The promethium EMFs were producedby the arc discharge method [2], [3] with DC 100 A under 60 kPa of He atmosphere. The produced
soot containing Pm EMFs was dissolved to CS2 and then filtered to remove insoluble substance. After
filtration, TiCl4 was added in this solution for the pre-separation of EMFs [4]. This pre-separated EMFs
solution was evaporated to dryness and then toluene was added to dissolve fullerene species for the
HPLC analysis.
2.3 HPLC analysis
The EMFs toluene solution was injected into HPLC system (Pump: Hitachi L-7110, flow rate: 3.2
mL/min, UV detector: GL-Science GL-7450, λ = 340 nm) with a HPLC column of Buckyprep (Nakarai
tesque inc., size: 10 φmm × 250 mm). The eluate from HPLC was collected for every 1 minute withthe range from 38 to 90 minute of the retention time. The γ-ray from each fractionated sample wasdetermined by a germanium semiconductor detector (SEIKO EG&G, GEM25P4).

§ 3. Results and Discussion
3.1 Produced radioactivity of Pm
Figure 1 shows γ-ray spectrum of irradiated Sm2 O3 sample with beam energy of 50 MeV. From
this spectrum 143 Pm (742 keV), 144 Pm (618 keV), 146 Pm (454 keV), 148m Pm (630 keV), 145 Sm (61keV), and 153 Sm (103 keV) were observed in this Sm sample. The productivities of each promethium
isotope with each beam energy were listed in table 1. The highest radioactivity was found to be that of143

Pm among these Pm isotopes. So the suitably longer half-life and higher radioactivity are required

for the metallofullerenes synthesis, we employed 143 Pm for the metallofullerenes synthesis.

137

Fig.1.

γ-ray spectrum of Sm2 O3 sample irradiated at the beam energy of 50 MeV.

Table 1. Determined productivity of each Pm isotopes.
Productivity [Bq/g·h]
143

Pm
144
Pm
146
Pm
148m
Pm
Target weight [g]20(1.2±0.1)×103
NA
NA
80±7
0.1069Beam Energy [MeV]30(3.4±0.3)×103NA36±7(6.1±0.3)×102
0.104640(8.8±0.9)×103
NA(1.5±0.3)×102(2.1±0.1)×103
0.106450(1.5±0.1)×104(1.4±0.2)×102(2.5±0.3)×102(3.9±0.2)×103
0.10433.1.1 HPLC elution behavior of Pm EMFs
According to the above mentioned results, 143 Pm was produced by the 50 MeV photon irradiationof Sm2 O3 for 6 hours. Figure 2 shows observed radioactivity of 143 Pm and 147 Nd for each HPLC fraction
together with obtained HPLC profile monitored by UV detector. The radioactivity of both 143 Pm and147

Nd was only observed at 62 min. In general, the metallofullerene M@C82 encapsulating trivalentlanthanide, such as La@C82 , Ce@C82 , Pr@C82 , Nd@C82 , etc., have almost same chemical properties aseach other and is observed around the HPLC retention time of 60 min under the studied condition (surrounded by an open square) [5]. On the other hand, metallofullerene encapsulating divalent lanthanide,such as Sm metallofullerenes, is known to be mainly eluted with empty fullerenes of C84 (around 40
min in this condition) [6], [7]. Considering about the HPLC elution behavior of trivalent and divalent
metallofullerenes, our results strongly suggest that observed radioactivity of 143 Pm together with thatof 147 Nd is derived from metallofullerene Pm@C82 encapsulating trivalent Pm.

Conclusion
Artificial element of Pm was produced by the photon irradiation at Research Center for Electron
Photon Science, Tohoku University. The highest productivity of Pm isotopes were found to be that of

138

Fig.2.

143

HPLC elution behavior of Pm metallofullerene.

Pm among the produced Pm isotopes in this study. Promethium metallofullerene was successfully

produced by arc discharge method. The valence state of Pm in produced metallofullerenes was strongly
suggested to be trivalent from the similarity of HPLC elution behavior for Pm metallofullerenes withthose for trivalent metallofullerenes.

Acknowledgment
We deeply thank to the facility staffs of research center for electron photon science at Tohoku University for supplying the high-quality electron beam. And also we thank to Professor Hidetoshi Kikunaga
and Doctor Kyo Tsukada for helping us in the sample irradiation.

References[1]

H. Shinohara: Rep. Prog. Phys. 63 (2000) 843.

[2]

W. Kratschmer et al.: Nature 347 (1990) 354.

[3]

K. Akiyama et al.: J. Am. Chem. Soc. 123 (2001) 181.

[4]

K. Akiyama et al.: J. Am. Chem. Soc. 134 (2012) 9762.

[5]

K. Akiyama et al.: J. Phys. Chem. A 104 (2000) 7224.

[6]

K. Sueki et al.: Chem. Phys. Lett. 291 (1998) 37.

[7]

T. Okazaki et al.: Chem. Phys. Lett. 320 (2000) 435.

ELPH Annual Report, Tohoku University (2014)

139(ELPH Experiment : #2787)

Measurements of thicknesses of Ce targets for (p,γ) reaction
Norikazu Kinoshita1, Shingo Ueno2
1
2

Institute of Technology, Shimizu Corporation, Koto-ku, Tokyo 135-8530

Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192
The thicknesses of 136Ce and 138Ce targets for the cross section measurements of the proton capture

reaction were determined using a photon activation analysis. The targets prepared with a plasma sputtering
process were activated together with natural Ce as a standard using a bremsstrahlung with a maximum energy of
20 MeV. Activities of 139Ce produced by the 140Ce(γ,n) reaction were determined with a gamma-ray spectrometry.
The thicknesses of 136Ce and 138Ce atoms were derived from the 139Ce activities, number of 140Ce atoms in thestandard, and nominal isotopic abundance used for preparation of the targets.

§1. Introduction
Most elements heavier than iron are synthesized via neutron capture processes known as the s process
and r process [1,2]. However, in the solar system, there are 35 neutron-deficient stable isotopes between Se andHg with low isotopic abundance. These nuclei, not created by the s process or r process, are termed p nuclei. The
p process, by which p nuclei are synthesized, proceeds via a photo-disintegration reaction [3-5], proton capture
reaction [6,7], and neutrino process [8] on the pre-existing heavy s and r seed nuclei at temperatures between 1.5− 3.5 GK. This high temperature can be obtained in explosive environments, such as in the O/Ne layers of Type IIsupernovae and in the deflagration flame fronts of Type Ia supernovae [9,10].
From the investigation of the isotopic abundance relative to atomic number Z, the p nuclei was found topossess approximately 1% abundance for lighter nuclei with Z = 34 − 50 and 0.01 − 0.3% abundance for medium
and heavier nuclei with Z > 50 [11]. The p nuclei with a larger atomic number have thus a smaller isotopic
abundance than that with a smaller atomic number. On the other hand, 92Mo and 144Sm with neutron magic
numbers present abundances of 14.77% and 3.07%, respectively. The neutrino process is a strong candidate forthe nucleosynthesis of 92Nb, 136, 138Ce, and 138La in the Type II supernovae [12,13]. The 12C(12C,p)23Na reaction is
one of candidate for the proton source in the Type Ia supernovae [6]. The neutrino process is hard to explain thegreater abundance of 92Mo and 144Sm. Photo-disintegration as well as the proton capture reaction has a key forunderstanding isotopic abundances of the overall p nuclei.
Our group have measured cross sections of (p,γ) and (p,n) reactions on 136, 138Ce, 142, 143Nd, 144Sm atenergies between ~3 MeV and ~8 MeV for an accurate numerical computation of abundances of the p nuclei withmass numbers of 130 − 150 in the stellar environment. Thin targets of the isotopes will be bombarded by the
proton beam for the cross section measurement. The thin targets were prepared using a molecular plating method

140

for isotopes of Nd and Sm [14]. Thicknesses of the targets are determined by measuring the solutions before andafter the molecular plating with an ICP-MS. On the other hand, targets of the Ce isotopes cannot be prepared by
the molecular plating method. Thus, we prepared the Ce targets with a plasma sputtering process [15]. The
prepared target is hardly dissolved in HCl or HNO3 because Ce is a refractory element; thickness of the target
cannot be determined with an ICP-MS. Activation analysis which allows to determine trace amount withoutsample digestion, is only method for measurement of the refractory element. In the present work, we intended todetermine the thicknesses of 136Ce and 138Ce target prepared by the plasma sputtering process using a photon
activation analysis.

§2. Experiment
Targets of enriched isotopes of 136Ce and 138Ce with a diameter of 7 mm were prepared using a plasma
sputtering process. The Ce isotopes were deposited on a 50-µm-thick aluminum foil with a purity of 99.999%.
Several targets of 136Ce and 10 mg of natural CeO with a purity of 99.9% sandwiched by Au foils as a flux
monitors with a diameter of 7 mm and thickness of 10 µm, were encapsulated in a quartz tube. The stack for
activation of 138Ce was prepared with the same manner as that of 136Ce mentioned above. A schematic diagram of
the target stacks is shown in Fig. 1.

136Ce or 138Ce

Pt converter

electron beamtargets

natural CeO

bremsstrahlung
quartz tube
quartz wool

Fig. 1

Au foilquartz wool

Configuration of target stack for activation using bremsstrahlung

The isotopic compositions of 136Ce and 138Ce enriched isotopes are summarized in Table 1 together witha natural Ce. The Ce has 4 isotopes of mass numbers 136, 138, 140, and 142. In an photon activation analysis,
activity of 139Ce with a half-life of 137.6 days produced by (γ,n) reaction from the most abundant nuclei of 140Ce
is the best for a gamma-ray spectrometry. The 139Ce can be produced by the 142Ce(γ,3n)139Ce reaction as well as
the 140Ce(γ,n)139Ce reaction. The thresholds of 140Ce(γ,n)139Ce and 142Ce(γ,3n)139Ce are 9.2 MeV and 21.8 MeV,
respectively. In the present work, bremsstrahlung with a maximum energy of 20 MeV was bombarded to suppress
142

Ce(γ,3n)139Ce reaction.

141

Table 1

Isotopic abundances of 136Ce, 138Ce, and natural Ce.
136

138

140

142

Ce-136

21.5%

1.3%

70.8%

6.4%

Ce-138

0.2%

12.9%

83.5%

3.4%

natural Ce

0.185%

0.251%

88.450%11.114%

Electron beams with 20 MeV for an energy and 100 µA for a beam current were bombarded to a
2-mm-thick Pt converter. The stacks were individually activated for 4 hours with bremsstrahlung with a maximum
energy of 20 MeV at 10 cm downstream of the Pt converter. After the activation, a gamma-spectrometry was
carried out using an HPGe detector at Kanazawa University.

§3. Results and discussion
Thicknesses of six targets each of 136Ce and 138Ce were determined in the present work. As an example,
gamma-ray spectra of natural Ce sample and one of targets of 136Ce and 138Ce are shown in Fig. 2. Gamma-ray
peaks of 139Ce produced by 140Ce(γ,n)139Ce reaction and 141Ce produced by 142Ce(γ,n)141Ce reaction wereidentified in all samples. Many peaks observed in the 136Ce sample were assigned to be 135Ce. Other significant
gamma-ray peaks were not identified in the spectra. Activities of 196Au, as of the end of irradiation, in the Au
monitor foils placed at downstream and upstream of samples were determined to be 23.8 ± 0.3 kBq/mg and 23.3 ±0.3 kBq/mg for the 136Ce stack, respectively. The activities in the 138Ce stack were determined to be 24.9 ± 0.3
kBq/mg and 24.9 ± 0.4 kBq/mg. We ignored variation of the bremsstrahlung flux in the stacks because the 196Au

Count rate (counts/sec/0.5 keV)

activity in the foils placed at downstream and upstream of samples agreed well each other within the errors.

Fig. 2

102
101

141

Ce

139

Ce

100

natural Ce
Ce-136Ce-138

10-1
10-2
10-3
10-4

0

200

400
600
Energy (keV)

800

100

Examples of gamma-ray spectra of natural Ce, 136Ce, and 138Ce activated with the bremsstrahlung.

142

Amounts of 140Ce atoms in each sample were determined by comparing number of 140Ce atoms innatural Ce as a standard, count rates of 139Ce in target samples and natural Ce as a standard. Thicknesses of 136Ceand 138Ce in each target prepared by a plasma sputtering process were calculated using the amount of 140Ce atoms
and nominal isotopic abundance as shown in Table 1. The thicknesses of 136Ce and 138Ce targets are summarizedin Table 2. Thickness of 136Ce and 138Ce in each target were determined to be ~1017 atoms/cm2 for 136Ce targets
and ~1016 atoms/cm2 for 138Ce targets. We’ll determine cross sections of (p,γ) and (p,n) reaction on these targets
using proton energies of 3 − 8 MeV.
Table 2 Thicknesses of the Ce isotopes in 136Ce and 138Ce targets prepared by a plasma sputtering process136

Ce (atoms/cm2)

138

Ce (atoms/cm2)

140

Ce (atoms/cm2)

142

Ce (atoms/cm2)

136

Ce target-1(5.00±0.15)×1016(3.02±0.09)×1015(1.65±0.05)×1017(1.49±0.04)×1016

136

Ce target-2(5.07±0.10)×1016(3.07±0.06)×1015(1.67±0.03)×1017(1.51±0.03)×1016

136

Ce target-3(1.44±0.03)×1017(8.71±0.19)×1015(4.74±0.11)×1017(4.29±0.10)×1016

136

Ce target-4(1.52±0.03)×1017(9.16±0.19)×1015(4.99±0.11)×1017(4.51±0.10)×1016

136

Ce target-5(7.03±0.14)×1016(4.25±0.08)×1015(2.31±0.04)×1017(2.09±0.04)×1016

138

Ce target-1(5.86±0.13)×1014(3.78±0.09)×1016(2.45±0.06)×1017(9.97±0.23)×1015

138

Ce target-2(7.39±0.13)×1014(4.77±0.09)×1016(3.08±0.06)×1017(1.26±0.23)×1015

138

Ce target-3(2.88±0.07)×1014(1.86±0.04)×1016(1.20±0.03)×1017(4.90±0.12)×1015

138

Ce target-4(5.78±0.11)×1014(3.73±0.07)×1016(2.41±0.05)×1017(9.83±0.19)×1015

138

Ce target-5(5.63±0.13)×1014(3.63±0.09)×1016(2.35±0.06)×1017(9.57±0.23)×1015

Acknowledgement
We wish to acknowledge the assistance of Dr. Kikunaga and the staff of ELPH, Tohoku University, withregard to the activation experiment and operation of the electron linac. This work was supported in part by aGrant-in-Aid for Scientific Research Program of Japan Society for the Promotion of Science (26800161).

References[1]

M. Arnould et al.: Phys. Rep. 450 (2007) 97.

[2]

F. Käppeler et al.: Rev. Mod. Phys. 83 (2011) 157.

[3]

M. Rayet et al.: Astron. Astrophys. 227 (1990) 271.

[4]

T. Rauscher et al.: Astrophys. J. 576 (2002) 323.

[5]

H. Utsunomiya et al.: Nucl. Phys. A 777 (2006) 459.

[6]

C. Travaglio et al.: Astrophys. J. 739 (2011) 93.

[7]

H. Schatz et al.: Phys. Rep. 294 (1998) 167.

[8]

C. Fröhlich et al.: Phys. Rev. Lett. 96 (2006) 142502.

[9]

T. Plewa et al.: Astrophys. J. 612 (2004) L37.

143

[10]

W. Rapp et al.: Astrophys. J. 653 (2006) 474.

[11]

J. Magill et al.: Chart of the Nuclides, 8th Edition, (EC-DG JRC-ITE, Karlsruhe, Germany, 2012).

[12]

T. Hayakawa et al.: Phys. Rev. C 77 (2008) 065802.

[13]

T. Hayakawa et al.: Astrophys. J. Lett. 779 (2013) L9.

[14]

W. Parker et al.: Nucl. Instr. Meth. 26 (1964) 61.

[15]

A. Caillard et al.: Pow. Sour. 162 (2006) 66.

144

ELPH Annual Report, Tohoku University (2014)

Profile measurement of bremsstrahlung at the irradiationsite for RI production.
H. Kikunaga for Radioactive-Isotope Science Group1
1

Research Center for Electron Photon Science, Tohoku University, Sendai, 980-8578

Profile measurement of bremsstrahlung at the irradiation site for RI production in the 1st Experimental Hall has been carried out by using a photon-activation method and autoradiography. The beamprofile is essential for estimation of the amount of the radioactivity produced in the photo-nuclear reactions.

§ 1. Introduction
Radioactive isotopes are useful for various applications in medical, pharmaceutical, chemical, physical, and biological sciences. Most of those are artificially produced in nuclear reactions using accelerators. In the Research Center for Electron Photon Science, Tohoku University, many radioactive isotopes
have been produced in the photo-nuclear reactions. However, the measurements of the production yieldsof the photo-nuclear reactions, which is essential for estimation of the amount of the radioactivity produced in a target, is difficult because that changes depending on the experimental setup. In many cases,
the production yields have been determined as the ratio of the production yield of a monitor reaction andthat of a reaction of interest. In other words, it is necessary for estimation of the amount of the radioactivity produced in the objective reactions to determine the production rate of the radioactivity producedin the monitor reaction with the experimental setup. In this report, we determined the production rateof a monitor reaction, namely nat Ni(γ,n)57 Ni reaction using our experimental setup.

§ 2. Experimental
The nickel foils with 10 µm thickness, 17 mm width, and 100 mm length were used as profile monitors. The 70 MeV electron linear accelerator at Research Center for Electron Photon Science, Tohoku
University was used. The accelerator was operated at electron energies of 20, 30, 40, and 50 MeV witha mean current of around 0.1 mA. The monitor foils were set in the water-cooling irradiation system
shown in Fig. 1 and were placed in 30 mm away from a platinum converter. The irradiation was carriedout for 3 minutes for each foils.
After the irradiation, the monitor foils were subjected to autoradiography using an imaging plate
to measure the distribution of radioactivities, which are mainly Ni-57 (T1/2 = 35.6 h [1].) produced inthe (γ,n) reaction. The imaging plate (BAS-IP-SR2025) was exposed by the monitor foils for 35 min after
approximately 25 hours from the end of bombardment.

145

Based on the results of the autoradiography, samples pieces with 10 mm diameter around the center of the radioactivity distribution were punched out from the Ni monitor foils, and then were subjectedto γ-ray spectrometry using a high-purity Ge semiconductor detector after 3 days from the end of bombardment.
10

30mm

SUS
1mm

Nifoil 10ʅm
100䘡17mm

Alsupport
1mm

Pt
2mm

eͲ
Bremsstrahlung

Water

Fig.1.

Water

Schematic diagram of the water-cooling irradiation system in the 1st Experimental Hall.

§ 3. Results
Fig. 2 shows photographic images taken using an imaging plate with a read-out spatial resolutionof 50 µm and their vertical and horizontal profiles. The photographic images are arranged in the orderof the electron energies of 20 MeV, 30 MeV, 40 MeV, and 50 MeV from the left side. The beam size of thebremsstrahlung at the irradiation site for RI production became smaller up to 40 MeV, and was almost
the same at 40 MeV and 50 MeV. A typical γ-ray spectrum for the Ni sample with 10 mm diameteris shown in the Fig. 2. The γ-peak of 57 Ni, which is the most prominent nuclide, 56 Ni, 57 Co, and56

Co are observed in the spectrum. The specific activities of 57 Ni normalized to the mass of irradiatedmaterial, beam current and duration of irradiation are 1.97(6) × 103 Bq/mg/µA/h for 50 MeV, 1.23(4) ×
103 Bq/mg/µA/h for 40 MeV, 6.00(17) × 102 Bq/mg/µA/h for 30 MeV, and 1.04(3) × 102 Bq/mg/µA/h for 20
MeV. Note that these values notably depends on the beam condition such as focus of the electron beam.
Unfortunately, the operation parameters of the accelerator have not determined due to the instabilityof its aging components. To provide for a stable supply of radioactive isotopes, the stabilization of theaccelerator is one of the necessary improvement.

References[1]R. B. Firestone and V. S. Shirley: Table of Isotopes, 8th ed.(John Wiley and Sons, New York, 1996).

146㻲㼃㻴㻹㼤㻌㻩㻌㻝㻤㻚㻟㻌㼙㼙㻲㼃㻴㻹㼤㻌㻩㻌㻝㻠㻚㻠㻌㼙㼙㻝㻜 㼇㼙㼙㼉㻝㻜 㼇㼙㼙㼉㻝㻜 㼇㼙㼙㼉

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㻠㻜㻌㻹㼑㼂㻜 㼇㼙㼙㼉

㻝㻣㻜㻡㻜㻌㻹㼑㼂

Photographic images taken using an imaging plateNi

57

Co, Ni

511 keVFig.2.

㻜㻝㻣㻣㻚㻠㻟㻜㻌㻹㼑㼂

㻲㼃㻴㻹㼥㻌㻩㻌㻝㻡㻚㻠㻌㼙㼙㻥㻜㻲㼃㻴㻹㼥㻌㻩㻌㻝㻣㻚㻞㻌㼙㼙㻝㻜㻜㻲㼃㻴㻹㼥㻌㻩㻌㻞㻜㻚㻜㻌㼙㼙㻲㼃㻴㻹㼥㻌㻩㻌㻞㻜㻚㻝㻌㼙㼙

㻝㻜㻜

㻝㻟㻟㻚㻢

56

Co

57

Ni

Ni
Co

56

56

Ni
56

Ni
56

103

57

Ni

Ni

104

56

Counts / channel

57

105

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㻝㻤㻣㻚㻝
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㻜㻲㼃㻴㻹㼤㻌㻩㻌㻟㻤㻚㻣㻌㼙㼙

102
101
100

0

500

Fig.3.

1000
Energy / keV

1500

An example of a γ-ray spectrum of a Ni sample.

2000

ELPH Annual Report, Tohoku University (2014)

147

Status of Accelerator Facilities in FY2014
Accelerator groupResearch Center for Electron Photon Science, Tohoku University, Sendai, 982-0826

The electron accelerator complex in this center consists of high intensity 60 MeV linac, 90 MeV
injector linac, 1.3 GeV booster synchrotron and 50 MeV linac as a test accelerator for coherent THz
source. Since the restart of user time in Dec. 2013, these machines have been well operated without any
significant trouble. In this report, machine status and some improvements performed in FY2014 arepresented.

§ 1. Low Energy Linac for RI Production
1.1 Overview of machine operation
Stable operating energies were 20, 30, and 50MeV with Linac repetition 300pps at the beginning.
As users requested the irradiation of a target with various energies, it is now extended 10 to 50MeV by
10MeV steps, and the beam currents are ranged from 80 µA to 120µA depending on the operated energy.
The machine is optimized for the mass production of radioactive isotopes that as much electron beam
should be transported to the target. Currently, the electron beam with ±10% of the operating energy
is transported to the experimental hall. Beam line at the experimental hall is only straight line along
upstream an accelerator beam line to achieve maximum transportation. Overall layout of 60MeV Linac
and the Experimental hall #1 is shown in Fig.1.
1.2 Guide electron beam to the target
The operation of 60MeV Linac is scheduled once or twice a week, and everything is shutdown
while there is no operation. Currently, it takes about an hour for starting-up a Linac before it is readyto irradiate the target. Comparing to the past, starting-up time is greatly reduced by employing 2
profile monitors to the downstream of experimental beam line. Beryllium plate with φ30mm and 0.5mm
thickness is used for tuning beam size and profile, and one with same dimension with φ10mm inner holeis used as a beam position monitor. Fig.2 shows Electron beam profile extracted to air (left ), and its
position before the target (right).
1.3 Beam extraction window
The electron beam is extracted from vacuum by 50 µm Ti film. The film was used to be sandwichedby flat surfaces of a conflate flange with φ 50mm inner opening and an air blower for cooling sealedwith indium paste. The flange was outdated standard, and the detail of Ti film was unknown except

148

Fig.1.

Fig.2.

Overall 60MeV Linac and the Experimental hall #1.

Electron beam profile extracted to air (left ), and its position before the target (right).

its thickness. This is now redesigned and replaced with the ICF152 conflate flange with φ 50mm inner
opening brazed Ti 99.5% film with 50µm thickness as shown in Fig.3.

149

Fig.3.

Beam extraction window brazed Ti film with 50µm thickness.

1.4 Beam Current Monitor
Beam current had been logged by an analog current averaging module and a digital current integrator. Now the system had been replaced with an oscilloscope averaging 4µs region of interest as shownin Fig.4. Logging is coincident with the control software of the Linac operation. It averages current pera pulse every a minute, and saves in user pc with time stamp. It would be automatically stopped whenan operator turned off a beam. Fig.5 shows an example of the current log after Ti window.

Fig.4.

Typical beam pulse of 50MeV operation. Channel 1: beam current at gun exit, Channel 2:
beam current after Ti window, Channel 3: RF pulse, and Channel 4: beam current after
A8.

150

Fig.5.

Current log after Ti window. Averaged (Blue) and total beam current irradiated (Red)§ 2. 90 MeV Injector Linac for the 1.3 GeV Booster Synchrotron
The injector linac employs a thermionic cathode RF gun with an alpha magnet as its electron source.
It consists of two independent cavities designed to manipulate the longitudinal phase space distributionof electron beam, named the Independently-Tunable Cells (ITC) RF gun. To obtain low emittance beam,a LaB6 single crystal cathode with a diameter of 1.78 mm had been used.
In the last year, it was observed that an emission current of the gun periodically drop during beam
operation, and it was not possible to perform a stable beam injection to the booster synchrotron. The
problem was short circuit of the cathode heater line with the ground, and it was found that temporally
revising an insulation of the cathode heater line helps to suppress this phenomena. For the best stable
operation, it was decided to replace the RF gun.
New RF gun is almost equivalent to the previous gun except it employs a CeB6 single crystal cathodewith a diameter of 3.0 mm. It adopted the cathode of a size larger than the previous one. It is aim
to suppress a back-bombardment effect for a stable operation without emittance deterioration. Mainparameters of new ITC RF gun are shown in Table 1.
Table 1. Main parameters of ITC RF gun.

Resonant frequency [MHz](cathode cell / accelerating cell)
Coupling (β)
Quality factor (Q0 )Shunt impedance (Rs ) [MΩ]

Design2856 / 2856

Measured
2855.9906 / 2856.0063

4∼59500 / 12500> 0.8 / >1.1

4.185 / 4.4071
8721 / 12000
0.886 / 1.271

151

Fig.6.

Cathode folder of new ITC RF gun

Fig.7.

Installed new ITC RF gun cavities

In new RF gun, a ceramic insulator was inserted into the cathode heater line to prevent a shortcircuit. In order to absorb the extension and distortion of the cathode posts due to thermal expansion,a metal spring was also adopted to the heater line as shown in Fig.6. In addition, a cooling efficiency

152of the RF gun cavities was improved by increasing the number of water channel to keep a constanttemperature of gun cavities for stable operation. New RF gun had been installed in the injector linac in
February, 2015 (Fig.7).

§ 3. 1.3 GeV Booster-storage ring (BST ring)
One of the main issues performed in FY2014 is the realignment of the synchrotron magnets. In
the early beam commissioning of the BST ring, we had encountered the problem of very large bare COD(closed orbit distortion), and then we could not circulate the beam without the steering magnets in spiteof the proper alignment accuracy. Furthermore, there are only four steering magnets for each plane
to correct the COD, so that we were forced to move two dipole magnets (BM4 and BM5) to inside thering more than 15 mm to mitigate the large horizontal COD. After some study to improve the machine
performance, it was turned out that the wrong positioning in some combined function magnets caused
this large COD. In some of these combined magnets to bring the sextupole component into the ring
optics, the mechanical fiducial plate had unusually large rotation angles with respect to the beam axis,
and thus these magnets should have to be positioned with their proper rotation angles. However, thosemagnets had been actually placed with wrong rotation angle due to the mishandling of the reference
coordinates based on the fiducial plate, so that it caused the large offset of magnetic center for thosecombined function magnets. In order to correct such offsets realignment was performed for all magnets
in February 2015, employing a laser tracker, Leica AT401, which has excellent resolution of the order of
0.01 mm for our typical situation.

Fig.8.

Displacements of the magnetic center in the reference coordinate system before (upper)
and after realignment work (lower). Red and blue plot show horizontal and verticaldisplacement, respectively. Note that the vertical scale is ten times magnified in lower
graph.

153

Fig. 8 shows displacements of the magnetic center with respect to the reference position, which wereobtained by using the reflector target mounted on the fiducial plate of each magnet. All the positionsof the magnets were carefully measured before moving those magnets for the realignment, and then it
was confirmed that some combined function magnets had actually large horizontal offsets more than
1 mm, which were consistent with the estimated values to explain the measured bare COD. It can bealso seen in the figure that the vertical displacement shows a sinusoidal behavior due to a slight tiltof the reference median plane. After the realignment work, displacements of the magnetic center werecorrected fairly well as shown in Fig. 8. Note that the vertical scale is ten times magnified in lower
graph.
Fig. 9 shows bare CODs before and after the realignment. As a result of the realignment, the largebare COD more than 20 mm in horizontal plane was improved drastically. Vertical bare COD was also
improved, and thus it became possible to accelerate some fraction of the injected beam to the maximum
energy without steering magnets. Two dipole magnets had been moved so far, however, those could goback to their original positions by the realignment. After the tuning work such as correction of COD,
phase-space matching for injection beam and modification of ramp-up patterns of synchrotron magnets
etc., the ring current more than 20 mA has been obtained with the maximum energy, which is almost
the same as the operated current before the disaster in spite of the much lower injection energy.

Fig.9.

Measured bare CODs before (blue) and after realignment work (red). Upper and lower
graph show horizontal and vertical CODs, respectively.

154§ 4. Improvements of control system and other infrastructure
4.1 Control system
Because of the limited human resources, we employed LabVIEW and EPICS for the control systemwith CA-lab to minimize the workload for developing the control software. The CA-lab was written by
Carsten Winkler and Tobias Hoff at BESSY and which can connect between LabVIEW and EPICS without any complicated procedure. Since all control and monitoring information of accelerators is sharedon the control system via the EPICS, our control system has a high extensibility for beam diagnosis,
data logging etc. Subcomponents of control system are roughly classified into the 90MeV injector, thebeam transport line, the BST-ring and the utility. Figure 10 shows schematic block diagram of the control system. It is easy to find the failure component in the accelerator by the logged data of about 2000
items of accelerator components. A snapshot of the parameter and status of the accelerators are saved
at intervals of every five minute, so that the condition of accelerator is easily understood. Since themaintenance of beam and the simple operation, such as beam on/off and change of duty cycle, have to
be also done by certified beam user in addition to the accelerator stuff in our facility, it is also importantto prepare a safe and simple program as a user interface for the less matured operator. Some tentative
programs for the beam commissioning still survive presently, and then further development for stable,easier and reliable operation of the accelerator is ongoing.

Fig.10.

Servers are operated on the virtual machine using Hyper-V. Network-attached storage(NAS) is used for backup of control system. The Database server is built using MySQL.
The Web server has distributed the information of accelerator status for users. To provide a secure operation of the accelerators, the control system accepts commands from
specific consoles.

155

4.2 Substation
There were some old substations and switchboards in the facility which were used exceeding theirservice lives, and thus it was difficult to keep the required functions with such old equipment. These
substations and switchboards provide the electric power for accelerators, experimental systems and air
handling units. Therefore there will be significant impacts on a controlled area for radiation in thefacility, if the power is cut off by failure of substation and switchboard. To avoid these potential risks
on safety management, we decide to replace the substation and the switchboard. However, due to thelimited budget for the replacement of such old equipment, we replaced the switchboard as a first step,
because the old protection relays were severely deteriorated. Next, the old substations will be replaced
as soon as possible for providing the stable electric power safely. Figure 11 shows the photograph of the
new switchboard.

Fig.11.

(left) Old switchboards, (right) new switchboards include vacuum circuit breakers (VCB)
and protection relays. An automatic power factor controller is also installed in the newswitchboard for proper control of the power system.

§ 5. Summary and prospect
Since the restart of user machine time on late in 2013, the approved beam time have been consumed
smoothly as scheduled. There were some improvements in FY2014, i.e. improvement of monitor system,
installation of new RF gun, realignment of synchrotron magnets, etc., which brought more reliable andstable operation for user. However there are still many instruments to be replaced or updated especiallyfor 60 MeV linac and BST ring, and thus it is important to pursue such improvement work continuously
not only to provide the regular user time but also to realize the higher performance of accelerator.

156

ELPH Annual Report, Tohoku University (2014)

User Support Office Report in FY2014
T. Ishikawa on behalf of the user support office1
1

Research Center for Electron Photon Science (ELPH), Tohoku University, Sendai 982-0826,
Japan

The User Support Office coordinates communication between the users and scientists at ELPH andmanagement of the beamtime. The bremsstrahlung photon beam came back in the end of December 2013
after the recovery of the 2011 Earthquake, and the experiments using electron/positron beams for testing
detectors started. The high intense low energy electron beam also came back, and the experiments using
it started in the end of February 2014.

§ 1. Introduction
Our facility has a 70 MeV electron linear accelerator (linac), a 1.3 GeV electron scynchrotron called
BooSTer (BST) ring with a 93 MeV injector. The two accelerator complexes providing electron and photon
beams are open to all the users in Physics and Chemistry. The beams utilized by the experimentalists
can be classified into three:
1. high intense low energy electrons (∼ 100µ A and 30 MeV, ∼ 120µ A and 50 MeV at maximum) for
producing radio active sources (Radiochemistry),
2. high energy tagged photons for meson photoproduction experiments (Hadron Physics), and3. positrons (electrons) with the variable energy for testing detectors (Particle Physics, Nuclear Physics,
and so on).
There was basically no difference between the latter two in the operation of the accelerator complex.

§ 2. Beamtime operated
The radiation time was 124.2 hours for the RI linac operation and 1130.9 hours for the BST operation, and it was 1255.1 hours in total. The beam provided time (user beamtime) was 154.0 and 822.4
hours for the RI linac and BST operations, and it was 976.4 hours in total. When the several experimental groups use the beamtime, the user beamtime is doubly counted. Table 1 summarizes the radiation
times, and user beamtimes in FY2014.
The 70 MeV electron linear accelerator was used for the Radiochemistry experiments. In November,producing extraordinary low energy beam down to 10 MeV was succeeded, and 10 MeV electrons were
provided to users. The high voltage supply controller for the 70 MeV electron linear accelerator wasout of order on 22nd in December. Low energy electron beams also came back in February after It was
repaired.

157

Table 1. Radiation times, and user beamtimes in FY2014. They are given by the sum of the times
that the beam is coming to the beamline, and that the beam is provided to the users. The
beamtimes are classified to RI linac and BST used ones.
month
April
May
June
July
AugustSeptember
OctoberNovember
DecemberJanuary
February
Marchsum

RI linacradiation (h) user (h)
13.7
6.9
3.0
7.2
22.1
29.1
0.0
0.0
0.0
0.0
0.0
0.0
25.0
21.0
22.2
40.3
7.2
7.4
0.0
0.0
3.2
2.8
27.8
39.3
124.2
154.0

BST
radiation (h) user (h)
113.7
73.8
141.4
91.6
121.7
112.2
21.6
0.0
29.5
0.0
207.4
173.1
3.7
0.0
182.9
146.2
213.6
204.3
3.5
0.0
14.2
0.0
77.8
21.2
1130.9822.4

Many experiments for testing detectors (mainly tracking devices, and particle identification counters) were made by using bremsstrahlung photon beams from the synchrotron. Although these photon
beams were provided in the parallel direction with respect to the temporary beamline (dx/dz = +0.14
mrad and dy/dz = +0.01 mrad) by moving the RTAGX magnet and the beam dump [1], the photon
beam intensity as a function of the spent time in a spill was different for different spills, namely theintensity of the provided positron beams was unstable. An increase of the intensity and an improvementof the profile of the positron beams especially for the low energy ones were made due to the installationof the vacuum chamber in March 2014 [2].
The meson photoproduction experiments did not start after the earthquake since the photon tagging counter was not ready for the photon beam course I and since a stable operation of the electron
synchrotron was not available for the photon course II. The unstable operation was thought to comefrom the mis-alignment of the magnets for the synchrotron. The rotation of the quadrupole magnets
were made step by step over this fiscal year to obtain a stable operation. The alignment of the magnets
was adjusted from the beginning in February and the BM4 and BM5 magnets (20–30 mm shift for the
temporary operation) became to the nominal position. The corresponding machine study was made inMarch, and also will be made in coming April of the next fiscal year. The injector linac was unstablein June, and it did not produce electrons for a while out of several minutes. It was replaced and thisphenomenon disappeared after the summer shutdown. The R&D works were still on-going for the newtagging counters for the two photon beam courses. The modification of the control system of the booster
ring was still continued.
Two experiments were proposed, and carried out for the undergraduate students. The first one(#2794: T. Ishikawa, ELPH, Tohoku University) is for the third school for giving an opportunity using
an accelerator to young undergraduate students (Y. Sakemi) [3], which was supported by High Energy

158

Accelerator Research Organization (KEK) for the corporations between Tohoku University and KEK (H.
Tamura). The second one (#2796: M. Miyabe, ELPH, Tohoku University) is for the education of theundergraduate students in ELPH.

§ 3. ELPH workshops and ELPH seminars
In this fiscal year, ELPH supported three ELPH workshops: the first on hadron physics (C009:
H. Fujioka, Kyoto University), the second on an electromagnetic calorimeter for particle, hadron, nuclear, and cosmic ray physics (C010: K. Miyabayashi, Nara Woman University), and the third on an
application of the high intense low energy electrons (C010: Y. Oura, Tokyo Metropolitan University).
Three ELPH seminars were held at ELPH: the first one on the development of a silica-aerogel (H. Kawai,
Chiba University, and M. Tabata, JAXA and Chiba University), the second one on the J-PARC hadronexperiments (K. Ozawa, KEK), the third one on the exotic hadrons from the point of the lattice QCD(T. Hatsuda, RIKEN).

References[1]

T. Ishikawa et al.: Commissioning of the photon beamline II after the recovery of the earthquake
in FY2013, ELPH annual report 2011–2013, 28 (2014).

[2]

T. Ishikawa et al.: Commissioning of the positron beamline for testing detectors after the recoveryof the earthquake in FY2013, ELPH annual report 2011–2013, 33 (2014).

[3]

Y. Sakemi: Web site hhttp://cycgw1.cyric.tohoku.ac.jp/ sakemi/cyric2014.htmli.

ELPH Annual Report, Tohoku University (2014)

放射線安全管理室報告
放射線安全管理室

Radiation Safety Report 2014
Radiation Control Office2014 年度（平成 26 年 4 月〜平成 27 年 3 月）
§ 1 . 変更申請
2014 年度の変更承認申請はない。

§ 2 . 個人管理
2.1 放射線業務従事者登録190 人（東北大 68 人、学外 104 人、研究者以外 18 人）
2.2 個人被ばく管理
1 年間の個人被ばく線量 5 mSv 以下 190 人
2.3 教育訓練
定期講習
平成 26 年 6 月 13 日 新規教育 16 人、 再教育 83 人
特別講演の内容：独立行政法人理化学研究所 仁科加速器研究センター
安全業務室長 上蓑 義朋 氏
「加速器施設の安全−理研 RIBF の経験から−」不定期の講習

32 回

112 人

§ 3 . 自主点検
年 2 回実施

平成 26 年 9 月 16 日、平成 27 年 3 月 26 日

159

160

§ 4 . 製造核種と数量
2014 年度に本加速器施設で製造され、共同研究に使用された放射性同位元素は次のとおり。
核種

数量 (kBq)

C-11

3000 kBq

N-13

3000 kBq

O-151000 kBq

Na-22

0.4 kBq

K-43

100 kBq

Sc-44m110 kBq

Ca-47

201 kBq

Sc-47

200 kBq

V-48

100 kBq

Cr-51

1500 kBq

Fe-52

1000 kBq

Mn-54

1 kBq

Co-57

1729.5 kBq

Ni-57

4300 kBq

Co-58

50 kBqZn-65

451.9 kBq

Ga-68

200 kBq

Sr-85

59.5 kBq

Y-88

21.9 kBq

Mo-99

710 kBq

Cd-10910.4 kBq

Sb-124

5 kBq

Ce-139

1 kBq

Pm-143100 kBq

Nd-147100 kBq

W-181

200 kBq

Au-196

2100 kBq

Pt-197200 kBq

全 28 核種

計 20,451.6 kBq§5 . そ の 他
第一実験室のγ線エリアモニタを更新（2013 年度実施）
第二実験室，光源加速器棟にγ線エリアモニタを増設（2013 年度実施）
第一実験室，第二実験室，光源加速器棟に中性子エリアモニタを新設

ELPH Annual Report, Tohoku University (2014)

161

List of Publication (論文リスト) (2014)
Papers Published in Refereed Journals′

Backward-angle photoproduction of ω and η mesons from protons in the photon energy range from 1.5
to 3.0 GeV
Y. Morino, Y. Nakatsugawa, M. Yosoi, M. Niiyama, M. Sumihama, T. Nakano, D.S. Ahn,
J.K. Ahn, S. Ajimura, W.C. Chang, J.Y. Chen, S. Daté, H. Fujimura, S. Fukui, K. Hicks, T. Hiraiwa, T. Hotta, S.H. Hwang, K. Imai, T. Ishikawa, Y. Kato, H. Kawai, M.J. Kim, H. Kohri,
Y. Kon, P.J. Lin, K. Mase, Y. Maeda, M. Miyabe, N. Muramatsu, H. Noumi, Y. Ohashi,
T. Ohta, M. Oka, J.D. Parker, C. Rangacharyulu, S.Y. Ryu, T. Saito, T. Sawada, H. Shimizu,
E.A. Strokovsky, Y. Sugaya, K. Suzuki, K. Tanida, A. Tokiyasu, T. Tomioka, T. Tsunemi,
M. Uchida, R. Yamamura and T. Yorita
Prog. Theor. Exp. Phys. (2015) 013D01. DOI: 10.1093/ptep/ptu167
Experiments at ELPH/Sendai before and after the disaster
H. Shimizu
International Journal of Modern Physics 26 (2014) 1460092. DOI: 10.1142/S2010194514600921
Search for the K− pp bound state via γd → K+ π − X reaction at Eγ =1.5-2.4 GeV
A.O. Tokiyasu, M. Niiyama, J.D. Parker, D.S. Ahn, J.K. Ahn, S. Ajimura, H. Akimune, Y. Asano,
W.C. Chang, J.Y. Chen, S. Date, H. Ejiri, H. Fujimura, M. Fujiwara, S. Fukui, S. Hasegawa,K. Hicks, K. Horie, T. Hotta, S.H. Hwang, K. Imai, T. Ishikawa, T. Iwata, Y. Kato, H. Kawai,
K. Kino, H. Kohri, Y. Kon, N. Kumagai, D.L. Lin, Y. Maeda, S. Makino, T. Matsuda, T. Matsumura, N. Matsuoka, T. Mibe, M. Miyabe, M. Miyachi, N. Muramatsu, R. Murayama, T. Nakano,
Y. Nakatsugawa, M. Nomachi, Y. Ohashi, H. Ohkuma, T. Ohta, T. Ooba, D.S. Oshuev, A. Sakaguchi, C. Rangacharyulu, S.Y. Ryu, T. Sawada, P.M. Shagin, Y. Shiino, H. Shimizu, E.A. Strokovsky,
Y. Sugaya, M. Sumihama, J.L. Tang, Y. Toi, H. Toyokawa, T. Tsunemi, M. Uchida, M. Ungaro, A. Wakai, C.W. Wang, S.C. Wang, K. Yonehara, T. Yorita, M. Yoshimura, M. Yosoi,
R.G.T. Zegers
Phys. Lett. B728 (2014) 616-621. http://dx.doi.org/10.1016/j.physletb.2013.12.039
Development of High Intensity Laser- Electron Photon Beams up to 2.9 GeV at the SPring-8 LEPS
Beamline
N. Muramatsu, Y. Kon, S. Daté, Y. Ohashi, H. Akimune, J.Y. Chen, M. Fujiwara, S. Hasegawa,T. Hotta, T. Ishikawa, T. Iwata, Y. Kato, H. Kohri, T. Matsumura, T. Mibe, Y. Miyachi,
Y. Morino, T. Nakano, Y. Nakatsugawa, H. Ohkuma, T. Ohta, M. Oka, T. Sawada, A. Wakai,
K. Yonehara, C.J. Yoon, T. Yorita, M. Yosoi
Nucl. Instr. Meth. A737 (2014) 184-194. http://dx.doi.org/10.1016/j.nima.2013.11.039
Performance test of a lead-glass counter for the J-PARC E36 experiment

162

Y. Miyazaki, S. Shimizu, S. Bianchin, C. Djalali, D. Gill, J. Jiang, M. Hasinoff, K. Horie,
Y. Igarashi, J. Imazato, A. Ivashkin, M. Kohl, R. Narikawa, R. Pywell, S. Strauch, M. Tabata,A. Toyoda, H. Yamazaki, T. Yoshioka Nucl. Instr. Meth. A779 (2015) 13-17.
Time-of-Propagation Counter for the LEPS
C.J. Yoon, H. Hamano, T. Hotta, Y. Kasamatsu, Y. Morino, Y. Nakatsugawa, T. Nakano,
T. Nam, H. Noumi, M. Oka, S.Y. Ryu, M. Yosoi, K. Matsuoka, Y. Kato, Y. Arita, K. Inami,
K. Suzuki, T. Hyakawa, T. Iijima, R. Maeshima, S. Hirose, Y. Horii, M. Niiyama, Y. Nozawa,
N. Muramatsu, E.A. Strokovsky, M. Uchida, M. Barrett, T. Browder, M. Jones, S. Korpar
IEEE Transactions on Nuclear Science, Vol. 61 (2014) 2601.
Electron Scattering for Exotic Nuclei
T. SudaPramana Journal of Physics 83, 2014, 739-747.
Production of 88 Nb and 170 Ta for chemical studies of element 105, Db, using the GARIS gas-jet system
M. Huang, H. Haba, M. Murakami, M. Asai, D. Kaji, J. Kanaya, Y. Kasamatsu, H. Kikunaga,
Y. Kikutani, Y. Komori, H. Kudo, Y. Kudou, K. Morimoto, K. Morita, K. Nakamura, K. Ozeki,
R. Sakai, A. Shinohara, T. Sumita, K. Tanaka, A. Toyoshima, K. Tsukada, Y. Wakabayashi,
A. Yoneda
Journal of Radioanalytical and Nuclear Chemistry 304 (2015), 845-849
Coprecipitation behaviors of Zr, Hf, and Th with Sm hydroxide for chemical study of element 104, Rf
Y. Kasamatsu, K. Toyomura, N. Shiohara, T. Yokokita, Y. Komori, A. Kino, T. Yoshimura,N. Takahashi, H. Haba, Y. Kudou, H. Kikunaga, T. Mitsugashira, T. Ohtsuki, K. Takamiya,
A. Shinohara
Journal of Nuclear and Radiochemical Sciences 14 (2014), 7-11
Comparison of the decay constants of 51 Cr with metal, oxide, and chromate chemical states
H. Kikunaga, K. Takamiya, K. Hirose, T. Ohtsuki
Journal of Radioanalytical and Nuclear Chemistry 303 (2015), 1581-1583
Production of 256 Lr in the 249,250,251 Cf + 11 B, 243 Am + 18 O, and 248 Cm + 14 N reactions
N. Sato, T.-K. Sato, M. Asai, A. Toyoshima, K. Tsukada, Z.-J. Li, K. Nishio, Y. Nagame,M. Schaedel, H. Haba, S. Ichikawa, H. Kikunaga
Radiochimica Acta 102 (2014), 211-219
Production of 262 Db in the 248 Cm(19 F,5n)262 Db reaction and decay properties of 262 Db and 258 Lr
H. Haba, M. Huang, D. Kaji, J. Kanaya, Y. Kudou, K. Morimoto, K. Morita, M. Murakami,
K. Ozeki, R. Sakai, T. Sumita, Y. Wakabayashi, A. Yoneda, Y. Kasamatsu, Y. Kikutani, Y. Komori, K. Nakamura, A. Shinohara, H. Kikunaga, H. Kudo, K. Nishio, A. Toyoshima, K. Tsukada
Physical Review C: Nuclear Physics 89 (2014), 024618/1-024618/11
Development of a Fast Timing Counter with a Monolithic MPPC Array
T. Nishizawa, Y. Fujii, H. Kanda, M. Kaneta, Y. Kasai, J. Kusaka, K. Maeda, S. Nagao,
S.N. Nakamura, K. Tsukada, F. Yamamoto

163

IEEE Trans.Nucl.Sci. 61 (2014) 3, 1278-1283
Experiments with the High Resolution Kaon Spectrometer at JLab Hall C and the new spectroscopy of
12ΛB hypernuclei
L. Tang, C. Chen, T. Gogami, D. Kawama, Y. Han, L. Yuan, A. Matsumura, Y. Okayasu,
T. Seva, V.M. Rodriguez, P. Baturin, A. Acha, P. Achenbach, A. Ahmidouch, I. Albayrak, D. Androic, A. Asaturyan, R. Asaturyan, O. Ates, R. Badui, O.K. Baker, F. Benmokhtar, W. Boeglin,
J. Bono, P. Bosted, E. Brash, P. Carter, R. Carlini, A. Chiba, M.E. Christy, L. Cole, M.M. Dalton, S. Danagoulian, A. Danie, R. De Leo, V. Dharmawardane, D. Doi, K. giyan, M. Elaasar,
R. Ent, H. Fenker, Y. Fujii, M. Furic, M. Gabrielyan, L. Gan, F. Garibaldi, D. Gaskel, A. Gasparian, E.F. Gibson, P. Gueye, O. Hashimoto, D. Honda, T. Horn, B. Hu, Ed V. Hungerford, C. Jayalath, M. Jones, K. Johnston, N. Kalantarians, H. Kanda, M. Kaneta, F. Kato,
S. Kato, M. Kawai, C. Keppe, H. Khana, M. Koh, L. Kramer, K.J. Lan, Y. Li, A. Liyanage,
W. Luo, D. Mack, K. Maeda, S. Malace, A. Margaryan, G. Marikyan, P. Markowitz, T. Maruta,
N. Maruyama, V. Maxwel, D.J. Millener, T. Miyoshi, A. Mkrtchyan, H. Mkrtchyan, T. Motoba,
S. Nagao, S.N. Nakamura, A. Narayan, C. Neville, G. Niculescu, M.I. Niculescu, A. Nunez, Nuruzzaman, H. Nomura, K. Nonaka, A. Ohtani, M. Oyamada, N. Perez, T. Petkovic, J. Pochodzalla, X. Qiu, S. Randeniya, B. Raue, J. Reinhold, R. Rivera, J. Roche, C. Samanta, Y. Sato,B. Sawatzky, E.K. Segbefia, D. Schott, A. Shichijo, N. Simicevic, G. Smith, Y. Song, M. Sumihama, V. Tadevosyan, T. Takahashi, N. Taniya, K. Tsukada, V. Tvaskis, M. Veilleux, W. Vulcan, S. Wells, F.R. Wesselmann, S.A. Wood, T. Yamamoto, C. Yan, Z. Ye, K. Yokota, S. Zhamkochyan,
and L. Zhu
Phys.Rev. C90 (2014) 3, 034320
Grid pulser for an electron gun with a thermionic cathode for the high-power operation of a terahertz
free-electron laser
S. Suemine, K. Kawase, N. Sugimoto, S. Kashiwagi, K. Furukawa, R. Kato, A. Irizawa, M. Fujimoto, H. Ohsumi, M. Yaguchi, S. Funakoshi, R. Tsutsumi, K. Kubo, A. Tokuchi, G. Isoyama
Nuclear Instruments and Methods in Physics Research A 773 (2015) 97-103
The high-power operation of a terahertz free-electron laser bsased on a normal conducting RF linac using
beam conditioning
K. Kawase, R. Kato, A. Irizawa, M. Fujimoto, S. Kashiwagi, S. Yamamoto, F. Kamitsukasa,
H. Osumi, M. Yaguchi, A. Tokuchi, S. Suemine, G. Isoyama
Nuclear Instruments and Methods in Physics Research A 726 (2013) 96-103
Local structure around Ge in lithium germanate glasses analyzed by AXS and EXAFS techniques
H. Arima, T. Kawamata, K. Sugiyama, J. Miner
Petrol. Sci. Adv. Pub., 2015 ,100, 141022f.
Temperature effect on screening effects and stopping power for low-energy d-6Li interaction in liquid Li
K.H. Fang, J. Zou, E. Yoshida, T.S. Wang and J. Kasagi
Europhys. Lett. 109 (2015) 22002-p1-p5; DOI: 10.1209/0295-5075/109/220

164

Papers Published in International Conference Proceedings
Investigation of Strangeness Photoproduction near the Threshold at ELPH, Tohoku University
M. Kaneta, B. Beckford, P. Bydz̆ovský, T. Fujibayashi, T. Fujii, Y. Fujii, K. Futatsukawa,
T. Gogami, Y. Han, O. Hashimoto, K. Hirose, K. Hosomi, R. Honda, A. Iguchi, T. Ishikawa,H. Kanda, Y. Kaneko, Y. Kasai, T. Kawasaki, C. Kimura, S. Kiyokawa, T. Koike, K. Maeda,
N. Maruyama, M. Matsubara, K. Miwa, Y. Miyagi, S. Nagao, S.N. Nakamura, T. Nishizawa,
A. Okuyama, M. Sotona, T. Tamae, H. Tamura, K. Tsukada, N. Terada, T. Wang, F. Yamamoto,
T.O. Yamamoto, H. Yamazaki, and the NKS2 collaboration
JPS Conf.Proc. 1 (2014) 013045.
Study of Double Delta Photoproduction on the Deuteron in the Energy Region of Eγ = 0.65 − 1.1 GeV
F. Yamamoto, B. Beckford1, T. Fujibayashi, T. Fujii, Y. Fujii, K. Futatsukawa, T. Gogami,
Y.C. Han, O. Hashimoto, K. Hirose, K. Hosomi, R. Honda, A. Iguchi, T. Ishikawa, H. Kanda,
M. Kaneta Y. Kaneko, T. Kawasaki, C. Kimura, S. Kiyokawa, T. Koike, K. Maeda, N. Maruyama,
M. Matsubara, K. Miwa, Y. Miyagi, S. Nagao, S.N. Nakamura, A. Okuyama, H. Shimizu,
K. Suzuki, T. Tamae, H. Tamura, K. Tsukada, N. Terada, M. Ukai, T.S. Wang, and H. Yamazaki
JPS Conf.Proc. 1 (2014) 013072.
Measurement of Charged Pion Photoproduction at ELPH
H. Kanda, B. Beckford, T. Fujibayashi, T. Fujii, Y. Fujii, K. Futatsukawa, T. Gogami, Y.C. Han,
O. Hashimoto, K. Hirose, K. Hosomi, R. Honda, A. Iguchi, T. Ishikawa, M. Kaneta, Y. Kaneko,
Y. Kasai, T. Kawasaki, C. Kimura, S. Kiyokawa, T. Koike, K. Maeda, N. Maruyama, M. Matsubara, K. Miwa, Y. Miyagi, S. Nagao, S.N. Nakamura, T. Nishizawa, A. Okuyama, H. Shimizu,
K. Suzuki, T. Tamae, H. Tamura, K. Tsukada, N. Terada, M. Ukai, T.S. Wang, F. Yamamoto,and H. Yamazaki
JPS Conf.Proc. 1 (2014) 013075.
Water/CH neutrino cross section measurement in J-PARC
T. Koga, N. Chikuma, F. Hosomi, M. Yokoyama, A. Bonnemaison,O. Drapier, O. Ferreira,
M. Gonin, Th. A. Mueller,B. Quilain,I. Aizenberg, A. Izmaylov, I. Karpikov, M. Khabibullin,
A. Khotjantsev, Y. Kudenko, S. Martynenko,A. Mefodiev,O. Mineev, T. Ovsjannikova,S. Suvorov, N. Yershov, T. Hayashino, A. K. Ichikawa, A. Minamino,K. Nakamura, T. Nakaya,
K. Yoshida, Y. Seiya, K. Wakamatsu, K. Yamamoto, Y. Hayato
Proceedings of the 2nd International Symposium on Science at J-PARC, to be published.
Production of Quasi-monochromatic GeV Photons by Compton Scattering using Undulator X-ray Radiation at SPring-8
H. Ohkuma, A. Mochihashi, M. Oishi, S. Suzuki, K. Tamura, T. Nakano, N. Muramatsu,
H. Shimizu
Proceedings of IPAC2014 (2014), 941-943.
The SCRIT Electron Scattering Facility

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T. Suda, A. Enokizono, M. Hara, Y. Haraguchi, S. Ichikawa, K. Kurita, S. Matsuo, T. Ohnishi,
T. Tamae, M. Togasaki, K. Tsukada, T. Tsuru, S. Wang, S. Yoneyama, M. Wakasugi
Proceedings of the 2nd Conference on

Advances in Radioactive Isotope Science 2014 , inpress
Study of Femtosecond Electron Bunch Generation at t-Acts, Tohoku University
S. Kashiwagi, F. Hinode, T. Muto, Y. Shibasaki, K. Nanbu, K. Takahashi, I. Nagasawa, S. Nagasawa, C. Tokoku, A. Lueangaramwong, H. Hama
Proc. of LINAC2014, (2014), pp1178-1181
Linear Focal Cherenkov-Ring Camera for Single Shot Observation of Longitudinal Phase Space Distribution for Non-Relativistic Electron Beam
K. Nanbu, H. Hama, F. Hinode, S. Kashiwagi, A. Lueangaramwong, T. Muto, I. Nagasawa,
S. Nagasawa, Y. Shibasaki, K. Takahashi, C. Tokoku
Proc. of IBIC2014, (2014), TUPF26
Lattice Design of a Sub-nm Emittance Storage Ring for a Compact High Brilliant Light Source, SLiT-J
H. Hama and SLiT-J Design Team
Proceeding of Advanced Lasers and Their Applications Workshop, Seogwipo, Jeju, Korea, May
8-10, 2014, pp
Structural Study of Fe80B20 Amorphous Alloy by Anomalous X-ray Scattering Coupled with Neutron
Diffraction
H. Arima, T. Kawamata, Y. Yokoyama, S. Kazumasa, T. Otomo
Proceedings of the J-PARC Symposium 2014, in press.

Invited Talk and Oral Presentations at International Conferences
Lattice Design of a Sub-nm Emittance Storage Ring for a Compact High Brilliant Light Source, SLiT-J
H. HamaAdvanced Lasers and Their Applications Workshop, Seogwipo, May 8-10, 2014, Jeju, Korea
Design strategy of a 3 GeV low emittance storage ring and a full energy injector linac for SLiT-J project
H. Hama
The 8th Asia Oceania Forum for Synchrotron Radiation Research (AOFSRR 2014), September
15 -18, 2014, Hsinchu, Taiwan
Design concept and expected performance of a 3GeV high brilliant synchrotron light source, SLiT-J
H. Hama
The 5th International Symposium of Advanced Energy Science, September 30 October 2.
2014, Uji, Kyoto
Conceptual Design of Variable Polarized THz Source Based on Crossed Undulator SuperradiantH. Hama
The 6th Asian Forum for Accelerators and Detectors (AFAD2015), January, 26-27, 2015,
Hsinchu, Taiwan

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Peculiar Physics by Intense Gamma Rays
H. Shimizu
International Workshop of Laser Compton Scatter Gamma Rays at Electron Storage Rings
Nov. 7-11, 2014, Saskatoon, SK, Canada.
Search for the η ‘ n bound state in the d(γ,p) reaction
N. Muramatsu
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Baryon spectroscopy at ELPH and LEPS2
T. Ishikawa
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Recent status and Physics overview at SPring-8 LEPS2/BGOegg
M. Miyabe
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
SCRIT Electron Scattering Facility
T. SudaThe 59th Annual Conference of the South Africa Institute of Physics, 7-11 July 2014,Johannesburg
Electron Scattering for Exotic Nuclei
T. SudaThe 38th Symposium on Nuclear Physics, January 6 11, 2015, Cocoyoc, Mexico
SCRIT Electron Scattering Facility
T. SudaARIS2014 (Advances in Radioactive Isotope Science）、June 1-6, 2014, Tokyo
Photonuclear Reaction of Exotic Nuclei at the SCRIT Electron Scattering Facility
T. SudaInternational collaboration SAMURAI meeting、September 8-9, 2014, Sendai
SCRIT Electron Scattering Facility
K. Tsukada
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
A luminosity monitor for the SCRIT electron scattering facility
S. Yoneyama
The 13th CSN summer school, Wako, August 21-27, 2014
The γn → K0 Λ photoproduction studied with an electromagnetic calorimeter complex FOREST
Y. Tsuchikawa
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Screening potential of the d(d,p)t reaction in liquid In and Sn measured for 10 ED3+ 60 keV
Y. Honda
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii

167

The performance study of an electromagnetic calorimeter BGOegg
Y. Matsumura
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Near threshold Λ(1115) photo production on a deuteron
B. Beckford
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Proposal of an experiment about Λ − n interaction via FSI in γ + d reaction at ELPH, Tohoku University
M. Kaneta
APS-JPS Joint Meeting, 7-11 Oct 2014, Hawaii
Test Experiment of Velocity Bunching in Accelerating Structure toward THz SuperradiantH. Saito
Korea-Japan Workshop on Accelerator Based Advanced Light Sources 2015, Korea, March
13, 2015

学位論文 (電子光理学研究センター所属)
博士論文「Bose-Einstein Correlations between two neutral pions from photoproduction below 1.2 GeV」
何 慶華（HE Qinghua），平成 26 年，東北大学
修士論文 「Development of Linear Focal Cherenkov-ring Camera for Direct Observation of Longitudinal

Phase Space of Non-relativistic Electron Beam」
Anusorn Lueangaramwong, 平成 26 年, 東北大学
修士論文 「進行波加速構造中における速度集群法を用いた極短パルス電子ビーム生成の研究」
永沢聡, 平成 26 年, 東北大学

修士論文 「制動輻射を用いた SCRIT 実験用ルミノシティモニタ」
米山 俊平, 平成 26 年, 東北大学
修士論文 「電磁カロリメータ BGOegg の性能評価」
松村 裕二, 平成 26 年, 東北大学

学位論文 (他機関所属)
修士論文「GeV 領域 γ 線ビームプロファイルモニターへの X 線ピクセル型検出器の応用研究」
尾関啓一,

平成 26 年度，東北大学

修士論文「中間子光生成反応実験に用いる内部標的型光子標識化装置の開発」
佐々木貴之,

平成 26 年度，東北大学

修士論文「J-PARC E07 実験用 momentum trigger に用いる ホドスコープ検出器の性能評価」
大植健一郎,

平成 26 年度，大阪大学

修士論文「ミューオン g-2/EDM 実験に用いるシリコン検出器の読み出し ASIC の開発」
調 翔平,

平成 26 年度，九州大学

修士論文「Development of a new GEM detector for a Cerenkov Counter application」

Hikari Murakami,

平成 26 年度，Graduate School of Science University of Tokyo

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修士論文「セリウム同位体の（p, γ ）反応実験及び陽子捕獲反応による p プロセスのモデル計算」
上野 慎吾,

平成 26 年度，金沢大学

修士論文「Research and development of a new neutrino detector for precise measurement of neutrino-

nucleus cross sections」
Taichiro Koga,

平成 26 年度，東京大学

修士論文「三次元格子構造を持つ新型ニュートリノ検出器 WAGASCI の開発」
吉田健人,

平成 26 年度，京都大学

修士論文「KOTO 実験における高レート多線式比例計数管のための波形整形機能をもつ信号増幅器の開発」
上路 市訓,

平成 26 年度，京都大学

修士論文「KOTO 実験の中性ビーム中で荷電粒子を検出する Thin Gap Chamber の開発」
中桐 洸太,

平成 26 年度，京都大学

学士論文「光量子放射化分析のための光核反応収率の測定 (II)」山口優貴,

平成 26 年度，首都大学東京

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Steering Committee
2014

Hajime SHIMIZU*

ELPH

Hiroyuki HAMA

ELPH

Toshimi SUDA

ELPH

Fujio HINODE

ELPH

Shigeru KASHIWAGI

ELPHNorihito MURAMATSU

ELPH

Hidetoshi KIKUNAGA

ELPH

Hirokazu TAMURA

Graduate School of Science

Teruya ISHIHARA

Graduate School of Science

Kazushige MAEDA

Graduate School of Science

Kouichi HAGINO

Graduate School of Science

Fuminori MISAIZU

Graduate School of Science

Yasushi KINO

Graduate School of Science

Asuka FUJII

Graduate School of Science

Atsuki TERAKAWA

Graduate School of of Engineering

Masaki FUJITA

Institute for Materials Research

Mihiro YANAGIHARA

Institute of Multidisciplinary Research for Advanced Materials

Keiichi EDAMATSU

Research Institute of Electrical Communication

Yasuhiro SAKEMI

Cyclotron and Radioisotope Center

Tetsuo TANIUCHI

Center for Interdisciplinary Research* Chairperson

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General Advisory Committee
2014

Hajime SHIMIZU*

ELPH

Hiroyuki HAMA

ELPH

Toshimi SUDA

ELPH

Hidetoshi KIKUNAGA

ELPH

Hirokazu TAMURA

Graduate School of Science

Yasushi KINO

Graduate School of Science

Yasuhiro SAKEMICYRIC

Tetsuo TANIUCHI

CIR

Hiroaki OHNISHI

RIKEN

Kyoichiro OZAWA

IPNS, KEK

Daisuke JIDOTokyo Metropolitan University

Takashi NAKANORCNP, Osaka University

Hideaki OHGAKI

IAE, Kyoto University

Shigemi SASAKIHSRC, Hiroshima University

Atsushi SHINOHARA

Osaka University

Keisuke SUEKI

University of Tsukuba* Chairperson

171

Program Advisory Committee
2014

Hiroyuki HAMA

ELPH

Toshimi SUDA

ELPH

Hidetoshi KIKUNAGA

ELPH

Kazushige MAEDA

Graduate School of Science

Satoshi N. Nakamura

Graduate School of Science

Asao YAMAMURA

Institute for Materials Research

Yasuhisa TAJIMA

Yamagata University

Toshiyuki TAKAHASHI *IPNS, KEK

Tomoaki HOTTA

RCNP, Osaka University

Yoshihiko SHOJILASTI, University of Hyogo

Keisuke SUEKI

University of Tsukuba

Yasuji OURATokyo Metropolitan University* Chairperson

173

平成 26 年度前期採択課題一覧
課題番号

課

題

名

申込責任者

原子核関連分野

2773

T2K 実験前置検出器施設に設置する新型ニュートリノ検出器のテスト実験

南野 彰宏

2776

大強度標識化ガンマ線ビームの透過率モニターの開発

石川 貴嗣

2777

FOREST 中央部における荷電粒子の極角測定装置の開発

石川 貴嗣

2779

Test experiment for new detector systems for the J-PARC E07 experiment

Sanghoon
Hwang

2780

FOREST 検出器の再整備とアップグレード

石川 貴嗣

2781

J-PARC E34 実験 (ミューオン g-2/EDM 実験) のためのシリコン飛跡検出器お三部

勉

よび読み出し回路の性能評価試験

2782

J-PARK E21 実験 (COMET 実験) のためのチェレンコフトリガー検出器の開発

東城 順治

放射化学関連分野

2774

光量子放射化法による 57 Co メスバウアー線源の作成

秋山 和彦

2775

光量子放射化分析のための光核反応収率の測定 (II)

大浦 泰嗣

2778

電子ライナックを用いた有用放射性トレーサー製造法の開発 II

菊永 英寿

2783

J-PARC E05 実験用 水チェレンコフ検出器の性能評価

永江 知文

2784

J-PARC E13 実験用 PWO 検出器読み出し回路の性能評価

鵜養 美冬

随時申込

174

平成 26 年度後期採択課題一覧
課題番号

課

題

名

申込責任者

原子核関連分野

2789

小型 Multigap Resistive Plate Chamber (MRPC) の性能評価

金田 雅司

2790

小型 ビームを用いた NKS2 実験スペクトロメータの動作確認及び調整

金田 雅司

2791

Photo-production of a Neutral Kaon and/or a Lambda Hyperon on a

金田 雅司

deuteron near the threshold
2793

J-PARC E14 実験用サンプリングカロリメータの性能評価

外川 学

2794

偏向電磁石のコイル電流と運動量分析される電子の運動量 [学生実験]

石川 貴嗣

2795

300 MeV 標識化光子ビーム生成のテスト

石川 貴嗣

2796

シンチレーションカウンターの基本的特性の研究 [学生実験]

宮部 学

2797

FOREST アップグレードのための粒子識別用チェレンコフ検出器の開発

河合 秀幸

2798

J-PARC E21 実験（COMET 実験）のためのドリフトチェンバー（CDC) の開

坂本 英之

発

2799

Feasibility study for Lambda-n interaction via FSI in gamma+d reaction

金田 雅司

2800

BM4 用 光子標識化装置の性能評価 （#2767 NKS2 実験のための光子ビームの神田 浩樹

調整の一部として）

2801

500 < Eγ < 800 MeV 領域における重水素原子核標的での π + π − 光生成反応

神田 浩樹

の研究

2802

チャームバリオン分光実験 (J-PARC E50) 用粒子識別チェレンコフ検出器のテ

野海 博之

スト実験

2803

光子ビームによる η メソン原子核の探索

石川 貴嗣

放射化学関連分野

2785

光量子放射化法によるプロメチウム（Pm）内包金属フラーレンの合成を目的と秋山 和彦

した RI 製造2786

軽元素の閾エネルギー近傍での光核反応断面積の測定

桝本 和義

2787

太陽系内同位体組成解明を目的とした光量子放射化分析

木下 哲一

2788

光核反応による核医学核種 Sc-44 の製造

福地 知則

2792

放射性バナジウム V-48 を用いたバナジウム・レドックスフロー電池の隔膜の研白崎 謙次

究 〜加速器による V-48 の製造〜
随時申込

2804

放射性ストロンチウムの化学分離法検討のための RI トレーサの製造

大浦 泰嗣