Experimental study of double
hypernuclei with hybrid emulsion methodat J-PARC
Workshop on Progress on J-PARC hadron physics in 20142014/11/30
Hiroyuki Ekawa
Kyoto University / JAEA
for the J-PARC E07 collaboration

Contents• Introduction- Double hypernuclei- J-PARC E07 experiment• Current status of detectors- Emulsion, KURAMA spectrometer, Hyperball X• ELPH test experiment- Setup- Result• Summary2

Contents• Introduction- Double hypernuclei- J-PARC E07 experiment• Current status of detectors- Emulsion, KURAMA spectrometer, Hyperball X• ELPH test experiment- Setup- Result• Summary3

Double hypernuclei• Double hypernuclei are important probes toinvestigate S = -2 physics.
- Y-Y interaction- ΛΛ-ΞN-ΣΣ mixing, H dibaryon• Emulsion experiment is efficient to detect
sequential weak decay from double hypernuclei

NAGARA event

previous experiments
experiment

Ξ stopdoubletwinhypernuclei hypernuclei

M.Danysz

41-

KEK E176~80

12

KEK E373~800

73BΛΛ = 6.91 ± 0.16 MeVΔBΛΛ = 0.67 ± 0.17 MeVΛΛ interaction showsweakly attractive

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J-PARC E07 experiment• 104 Ξ- stop in emulsion
100 double hypernulei candidates- 10 identified species- Mass dependence of ΛΛ interaction

Ξ-K-

K+-

diamond targetSSD• Hybrid emulsion method
combine counters and emulsion- automatic scan-emulsionplateΞ- track of SSD and emulsion
can be connected automatically.
expected spectrum for X ray• X ray from Ξ- atom
study about surface region of
Ξ- nucleus potential- background is suppressed bytagging Ξ- stop.
- first measurement in the world-Ag(370.45 keV)Br(315.5 keV)Eγ [kev]5

K1.8 beam linewith SKSSetup• K1.8 Beam line w/ KURAMA spectrometer@J-PARC Hadron Experimental facility• p(K-, K+)Ξ+ reaction• 1.67 GeV/c K- beam (300k/spill, K/π = 6)
• 1 month data taking

K-

QQDQ
magnets

collimator

Beam Line
Spectrometer

SKS

Diamond
Target

KURAMA
magnetK+

Ξ-Emulsion
SSD
Hyperball X

KURAMA
Spectrometer6

Contents• Introduction- Double hypernuclei- J-PARC E07 experiment• Current status of detectors- Emulsion, KURAMA spectrometer, Hyperball X• ELPH test experiment- Setup- Result• Summary7

Emulsion• Emulsion gel was made by Fujifilm.
• 2.1 t emulsion mass production was done.

(~110 stacks)• Emulsion plates are stored in Kamioka mine andsurrounded by lead block.
• Noise track accumulation is monitored.

Emulsion mover• Emulsion will be moved to be irradiated flatly for all region.
• position accuracy : ~10µm• SSD will be mounted to Emulsion mover.
• performance test is ongoing.
8SSD•••••

4 layers (XYX’Y’)effective area : 77 mm x 77 mm
pitch size : 50µm
angular resolution : ~20 mrad
2 layers prototype (XY) was fabricated and tested.

Noise of new sensor was quit larger than previous one(especially X sensor). By changing GND connection
etc., we achieved S/N ratio as more than 10.
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KURAMA magnet
BH2
KURAMA magnet• used at KEK-PS (E373)• gap size was enlarged 50 -> 80 cm.
• coil was reconstructed.
• magnet filed was measured with end guard.
• acceptance : 280 msr

BH2 (Beam Hodoscope)• start timing counter• effective area : 120 mm x 40 mm x 6 mm
• 2’’ PMT x 2 w/ light guild
10BAC・PVAC・FAC
BAC (Beam Aerogel Cherenkov counter)• index : 1.03
• effective area : 160 mm x 75 mm• 3’’ FM-PMT x 2• veto beam π
PVAC (Proton Veto Aerogel Cherenkov counter)• index : 1.164• effective area : 117 mm x 117 mm• 2.5’’ FM-PMT x 4• veto low momentum proton• prototype was fabricated
FAC (Forward Aerogel Cherenkov counter)• index : 1.05
• effective area : 220 mm x 180 mm• 2.5’’ FM-PMT x 6• veto π and beam• FAC have not been fabricated11CH(Charge Hodoscope)
••
•
•
•

3D Matrix trigger (FBH & CH & TOF)
64 segments
scintillator w/ WLS fiber
MPPC w/ EASIROC board
effective area : 673 mm x 450 mm
scintillator + WLS fiber
wrapped by Teflon

2 p.e.
1 p.e.
pedestal

ADC spectrum of MPPC w/ EASIROC 12

FBH(Fine Beam Hodoscope)••••

16 segments
scintillator w/ WLS fiber
new MPPC w/ EASIROC board
effective area : 82.5 mm x 35 mm>15 p.e.
adc[ch]ADC spectrum of MPPC w/ EASIROC

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TOF
• 24 segments• effective area : 1805 mm x 1800 mm• wrapped by aluminized mylar and black sheet• intrinsic time resolution : 90 ns• cosmic ray test bench is ready90ns

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Drift Chambers
Noise reduction and signal checkare ongoing.

DC3• 4 layers (XX’YY’)• 1920 mm x 1280 mm• wire spacing : 20 mm

DC1• 6 layers (XX’UU’VV’)• effective area : 400 mm x 250 mm• wire spacing : 6 mm
• used at K1.8BR

time distribution (DC3)countsDC2• 4 layers (XX’YY’)• 1186 mm x 1186 mm• wire spacing : 9 mm
• used at KL beam line

nscorresponding to drift region

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Hyperball X• detect X ray from Ξ- atom
• 6 units of clover-type Ge detector• frame is stored at Tokai.
• Ge detectors are under maintenance.
• photo peak eff : 3%

Clover-type Ge16

Contents• Introduction- Double hypernuclei- J-PARC E07 experiment• Current status of detectors- Emulsion, KURAMA spectrometer, Hyperball X• ELPH test experiment- Setup- Result• Summary17

ELPH test experiment•••carried out in June 2014.
e+ beam converted from GeV γ37 conditions had been tested.

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SetupGeV gamma hall

• 500 MeV/c e+ beam
• large trigger : 144 mm x 44 mm• small trigger : 9.3 mm x 9.3 mm• trigger rate : 5000 / spill (large)• tight cut (small trig & no shower) : ~1%

CHBAC
SSD

BH2e+ beam

PVAC
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npe(number of photoelectron)

BAC

mean npe : 27.4

Teflon• compare reflection material (Teflon & Gore Tex)
• Teflon shows better result.
• npe is good enough at each position.

mean npe : 23.8

Gore Texposition dependence
irradiated position

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simulation

PVAC

mean npe : 20.1

npe

Y [cm]

position dependence

data32

32
33

20.1

32

npe

31

X [cm]• Data have large tale because of PMT characteristic.
• npe is similar to simulation and position dependence is small.

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multiplicity of old and new sensor

SSD

hit profile (new sensor)• Two old sensor SSD were used as reference.
• Performance of new sensor was almost same as oldsensor except for noise.

22CHgain difference of all MPPC•••

Y position dependence

all MPPCs have similar gain.
efficiency : 99.9 % (th : 5.5 p.e.)position and angle dependence is small.

angle dependence23

EJ-212, Al Mylar (MIP : 280 ch)
EJ-230, Al Mylar (MIP : 100 ch)
EJ-230, Teflon (MIP : 230 ch)

BH2

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

80 ps

80 ps

H10570H2431-50

PMT specification• 2 types of PMT were tested.

H10570H2431-50• low gain data shows bad result.

HV-1500 V-3000 V(slewing factor is dominant)• 80 ps is good enough to detect scatteredgain

5.0 x 105

2.5 x 106

rise time

1.8 ns

0.7 nstransit time spread

250 ps370 pskaon.

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Contents• Introduction- Double hypernuclei- J-PARC E07 experiment• Current status of detectors- Emulsion, KURAMA spectrometer, Hyperball X• ELPH test experiment- Setup- Result• Summary25

Summary• J-PARC E07 experiment is a double hypernuclei

search experiment.
• Test experiment was carried out at ELPH in June2014 and performance of several detectors wereevaluated.
• Preparation of E07 have been almost done.

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