1COMET experimentsearch for muon to electron conversion

Hisataka Yoshida

for the COMET Collaboration

28th Sep. 2018 @ New Trend in High Energy Physics in Montenegro

Contents• Introduction• Overview of COMET experiment• Status of COMET Phase-I• Prospects for Phase-II• Summary2

an illustration by higgstan.com

3

Charged Lepton Flavor Violation
The establishment of the Standard Model and the observation of the Neutrino
Oscillation worked-out very much in the particle physics.
However, There are still mysteries like- dark matter ?? / dark energy?

- why does our universe consist of dominant “matter” ? (not anti-matter)- absolute neutrino mass ? why so small ?

Processes of the CLFV- highly prohibited (O(<10-54)) in the
SM with Neutrino Oscillation(= no/less SM background)- are very rare events/decays- not found yet !
- if found, immediately indicatessomething beyond the SM

Thatʼs why “CLFV” is interesting!

μ - e conversion search
1. Generate “muonic atom” by muon stopping at the target
2. Measure emitted electron momentum from muonic atom
A. spectrum of decay in orbit is Michael edge and longer tail up to 105 MeV
B. μ-e conversion signal is a mono-energetic ~ 105 MeV peak(neutrinoless muon decay → emitted electron has all energy of the decay)
3. Spectroscopic search for μ-e conversion signal

Backgrounds

in the SM
Decay In Orbit (DIO)

Muon Capture

Signal beyond the SM
μ- e conversion

muonic atommuonic atom

Nucleusμ­

τ~ 1μsec

μ + N → νμ+ N

Nucleus

μ

μ

­

­

νμ

* electron not emitted

Nucleus

νμ
­

ーe
ν

e

ー
μ → e ννe μ­eμN → e N

4.

The COMET Collaboration
ation

ai

Strong contributions from Asian countries
•3

4

•

The COMET Collaboration

Enhancing collaboration using JSPS bilateral research program

R. Abramishvili11 , G. Adamov11 , R. Akhmetshin6, 31 , V. Anishchik4 , M. Aoki32 ,Y. Arimoto18 , I. Bagaturia11 , Y. Ban3 , A. Bondar6, 31 , Y. Calas7 , S. Canfer33 ,Y. Cardenas7 , S. Chen28 , Y. E. Cheung28 , B. Chiladze35 , D. Clarke33 ,M. Danilov15, 26 , P. D. Dauncey14 , W. Da Silva23 , C. Densham33 , G. Devidze35 ,P. Dornan14 , A. Drutskoy15, 26 , V. Duginov16 , L. Epshteyn6, 30, 31 , P. Evtoukhovich16 ,G. Fedotovich6, 31 , M. Finger8 , M. Finger Jr8 , Y. Fujii18 , Y. Fukao18 , E. Gillies14 ,D. Grigoriev6, 30, 31 , K. Gritsay16 , E. Hamada18 , R. Han1 , K. Hasegawa18 , I. H. Hasim32 ,O. Hayashi32 , Z. A. Ibrahim24 , Y. Igarashi18 , F. Ignatov6, 31 , M. Iio18 , M. Ikeno18 ,From Wikipedia, the free encyclopedia
K. Ishibashi22 , S. Ishimoto18 , T. Itahashi32 , S. Ito32 , T. Iwami32 , X. S. Jiang2 ,This article is about the European country. For otherP.
uses,Jonsson
see Belarus14(disambiguation).
, T. Kachelhoffer7 , V. Kalinnikov16 , F. Kapusta23 , H. Katayama32 ,K. Kawagoe22 , N. Kazak5 , V. Kazanin6, 31 , B. Khazin6, 31 , A. Khvedelidze16, 11 ,Republic of Belarus T. K. Ki18 , M. Koike39 , G. A. Kozlov16 , B. Krikler14 , A. Kulikov16 , E. Kulish16 ,Y. Kuno32 , Y. Kuriyama21 , Y. Kurochkin5 , A. Kurup14 , B. Lagrange14, 21 ,Рэспубліка Беларусь (Belarusian)M. Lancaster38 , M. J. Lee12 , H. B. Li2 , W. G. Li2 , R. P. Litchfield14, 38 , T. Loan29 ,Республика Беларусь (Russian)
D. Lomidze11 , I. Lomidze11 , P. Loveridge33 , G. Macharashvili35 , Y. Makida18 ,Y. Mao3 , O. Markin15 , Y. Matsumoto32 , A. Melnik5 , T. Mibe18 , S. Mihara18 ,F. Mohamad Idris24 , K. A. Mohamed Kamal Azmi24 , A. Moiseenko16 , Y. Mori21 ,M. Moritsu32 , E. Motuk38 , Y. Nakai22 , T. Nakamoto18 , Y. Nakazawa32 , J. Nash14 ,J. -Y. Nief7 , M. Nioradze35 , H. Nishiguchi18 , T. Numao36 , J. O’Dell33 , T. Ogitsu18 ,K. Oishi22 , K. Okamoto32 , C. Omori18 , T. Ota34 , J. Pasternak14 , C. Plostinar33 ,45
V. Ponariadov, A. Popov6, 31 , V. Rusinov15, 26 , B. Sabirov16 , N. Saito18 ,FlagNational emblem
H. Sakamoto32 , P. Sarin13 , K. Sasaki18 , A. Sato32 , J. Sato34 , Y. K. Semertzidis12, 17 ,Anthem:N. Shigyo22 , D. Shoukavy5 , M. Slunecka8 , A. Straessner37 , D. Stöckinger37 ,Дзяржаўны гімн Рэспублікі Беларусь (Belarusian) 18
M. Sugano , Y. Takubo18 , M. Tanaka18 , S. Tanaka22 , C. V. Tao29 , E. Tarkovsky15, 26 ,Dziaržaŭny himn Respubliki Bielaruś
35
29
32
22
10
18
Y.
Tevzadze
,
T.
Thanh
,
N.
D.
Thong
,
J.
Tojo
,
M.
Tomasek,
M.
Tomizawa,(English: State Anthem of the Republic of Belarus)
32
29
35
32
16, 11N. H. Tran , H. Trang , I. Trekov , N. M. Truong , Z. Tsamalaidze
,
0:00
MENU
16, 35
18
14
18
16
16
N. Tsverava, T. Uchida , Y. Uchida , K. Ueno , E. Velicheva , A. Volkov ,10
V. Vrba , W. A. T. Wan Abdullah24 , M. Warren38 , M. Wing38 , M. L. Wong32 ,T. S. Wong32 , C. Wu2, 28 , H. Yamaguchi22 , A. Yamamoto18 , T. Yamane32 , Y. Yang22 ,W. Yao2 , B. K. Yeo12 , H. Yoshida32 , M. Yoshida18 , Y. Yoshii18 , T. Yoshioka22 ,Y. Yuan2 , Yu. Yudin6, 31 , J. Zhang2 , Y. Zhang2 , K. Zuber37+ moreRussia, India, Georgia, and China

Eﬀorts to call for providing institute resources

Belarus•5

CC-IN2P3 & Yandex

7 collaborators

einstitutes
117 collaborators
27 institutes
200+ collaborators,
apan 4012
countries
institutes
countries
012 from 17 countries

6

COMET Experiment
Search for “μ-e conversion” in Japan at J-PARC hadron hallExperimental Target :B(µ + Al ⇥ e + Al) = 2.6
3.3
B(µ + Al ⇥ e + Al) < 7

10 17 (S.E.S)
10 17(90%C.L.)

This is 10,000 times improvementfrom the current limit given by the SINDRUM II experiment (2006).
Current World Limit :B(µ + Au ⇥ e + Au) < 7

10 13

Important Keys for COMET

1. Increase of Muon Intensity with an Innovative Pion Capture System
MuSIC in RCNP-Osaka University demonstrated more than x 103 improvementof pion capture eﬃciency with larger target and surrounding superconducting
solenoid to capture pions.

2. Reduction of Background by Detector System and Pulsed-BeamBackgrounds Reduction

DIO

Intrinsic BackgroundDIO spectrum has longer tail up to ~105 MeV→ require high momentum resolution of the detector
to separate the DIO tail and signal(extinction factor = # of proton after bunch / # of proton in 1 bunch)7

the DIO electrons is presented in Section 17.2. In this study, the momentum cut of 103.6 MeV/c7 <Pe < 106.0 MeV/c, where Pe is the momentum of electron, is determined as shown in Fig. 107 [61]According to this study, the contamination from DIO electrons of 0.01 events is expected for a singl
event sensitivity of the µ− N → e− N conversion of 3.1 × 10−15 .

Backgrounds Reduction
Signal and DIO (BR=3 × 10-15)

Counts per 0.1 MeV/c

0.18
0.16

Signal

0.14
0.12
0.1
0.08
0.06

DIO

DIO

0.04
0.02
0
101.5

102

102.5

103

103.5

104

104.5

105
105.5
106
Momentum [MeV/c]

Intrinsic Background
DIO106:
spectrumhas longer
up to ~105
MeV
FigureLeft: Distributionsof the tailreconstructedµ− N →
e− N conversion signals and reconstructed DIO
events.
The verticalscalemomentum
is normalized so thatthe integrated
area
ofdetector
the signal is equal to one event with it→ requirehighresolution
ofthebranching ratio of B(µN → eN ) = 3.1 × 10−15 . Right: The integrated fractions of the µ− N → e− N conversion
tointegration
separatethetailsideandsignalsignals and DIO events as a function of the low side of therange
andDIOthe highof theintegration

range is 106 MeV/c. The momentum window for signals is selected to be fro 103.6 MeV/c to 106 MeV/c s
that the DIO contamination would be 0.01 events.

16.1.4

Time window for signals(extinction factor = # of proton after bunch / # of proton in 1 bunch)the DIO electrons is presented in Section 17.2. In this study, the momentum cut of 103.6 MeV/c7 <The COherent
Muon to Electron Transition
Beam
for
COMET
Pe < 106.0 MeV/c,Proton
where Pe is
the momentumofelectron,is determined as shown in Fig. 107 [61](COMET) experimentAccording to this study, the contamination from DIO electrons of 0.01 events is expected for a singl− N conversionBeam
forevent sensitivity of the µ− N → eProtonof 3.1 × 10−15. COMET

Backgrounds Reduction•

Muonic lifetime is dependenton-15
Signal target
and DIO
10 ) is 880ns.
Z. (BR=3
For Al×lifetime
Bunch Structure
Bunch Separation
1.3 µsCounts per 0.1 MeV/c

0.18
0.16

100ns
Signal0.14

Bunch Length

0.12

Protons per Bunch

1.2x108

0.1

Bunches per Spill

5.3x105

0.08
0.06

DIO

0.04

DIO
Spill time

Extinction

0.7s
10-9

•

0.02
0
101.5

102

Background rate needs to be low in orderto achieve sensitivity of <10-16.
Extinction
is very102.5 • 103
103.5
104
104.5important.
105
105.5
106
Momentum [MeV/c]– Without sufficient extinction, allin prompt background
Intrinsic Backgroundprocesses
category could become a problem.

Ajit Kurup
Tau ~105
2010
DIO106:
spectrumhas
longerup to
MeVPage 11
FigureLeft: Distributionsof the tailreconstructedµ−13
N September→
e− N 2010
conversion signals and reconstructed
DIO
events.
The verticalscalemomentum
is normalized so thatthe integrated
area
ofdetector
the signal is equal to one event with it→ requirehighresolution
ofthebranching ratio of B(µN → eN ) = 3.1 × 10−15 . Right: The integrated fractions of the µ− N → e− N conversion
tointegration
separatethetailsideandsignalsignals and DIO events as a function of the low side of therange
andDIOthe highof theintegration
Beam-related
Background
range is 106 MeV/c.
The momentum window for signals is selected to be fro 103.6 MeV/c to 106 MeV/c s
that the DIO contamination would be 0.01 events.
thRadiative pion capture, muon decay in ﬂight and so on→ require pulsed beam and excellent proton extinction < 10-10

16.1.4

Time window for signals(extinction factor = # of proton after bunch / # of proton in 1 bunch)COMET
at
J-PARC
E21
J-PARC layout
View from HD Facility Entrance
Nov. 2014

Main Entrance
14

COMET beam-line at J-PARC HD


2012-8-14

Hai-Bo LI (IHEP)

11

built in 2015

8

9

COMET Phase-I
COMET Phase-I Goal :B(µ + Al ⇥ e + Al) = 3.0
3.3
B(µ + Al ⇥ e + Al) < 77

15 (S.E.S)
10 17
15
10 17

(90%C.L.)・With shorter muon transport solenoid (90 bending)・Not-full power operation of proton beam (3.2 kW)
・Quick and Low-Cost Construction to get result earlier- under construction since ~2013, budget funded (almost fully).
- will be completed the detector construction in 2019
・Containing R&D for Phase-II
6. Muon Beam
Muon transport
Pion production
detector for- Background Measurementµ-e conversion- Detector Study and Development
・COMET Project is approved by
J-PARC in summer 2016
・Technical Design Report is
COMET
Phase-I Layout
being updated as 2018 version.
detector systemmuon transport systempion production system
Figure 26: Overview of the COMET Phase-I Muon Beam line.

10

COMET Phase-I Detectors

CDC

StrawECAL

1T
B-field••••

Cylindrical Drift Chamber
for physics search in Phase-I
muon stopping target at center~20,000 wires with He base gas•••

Straw Tracker+ Electron Calorimeterfor beam background measurement
also as R&D for Phase-II

Cylindrical Drift Chamber

11

COMET CDC
CDC endplate- Surrounding target
Stopping target- 19 layers structureμe~5,000 sense wires~15,000 ﬁeld wires- All stereo layers- He base gas
Trigger hodoscope(He : iC4H10 = 90 : 10)
Vacuum window
Cryostat
Return yoke
- Study of prototype chamber is done
- basic performance study was done, it is OK- spatial resolution < 200 μm obtained- wire aging test is almost done
- Design was ﬁxed based on Belle-II CDC with modiﬁcation for COMET- Construction started in 2014, and completed in 2016
- Commissioning with cosmic-ray is ongoing in KEK now
Superconducting coils

CDC inner wall

CDC outer wall

CDC

ed XT curve, spatial resolution and hit
5thefficiency-pol functionfor the layer.
d the event which meets condition of event selection.

12

5th-pol function
and linear function
COMET
CDC
Commissioning
ments for event

DCA =Distance Closest Approach

Fitting function for XT

Spatial resolution0…
t < 0ns
5th pol function … 0ns ≤ t < 350ns
f t =linear function … 350ns ≤ t < 700ns
N⁄A … 700ns < t

ve which corresponds to the relation
distance and drift time for CDC.
2017/9/26

Get σ of residual to understand spatial redrift time [ns]

XT CM23
curve
for forlayer
Residuallayer10
10COMET

spatial resolution

entry
entry

layer 10Drift Distance [mm]XTCurve<Hit condition for XT Curve>
X-T curve
racking>0.05• Hit on the test layer
which has single hit >14
Residual =radius of drift circle – |DCA|• P value of tracking>0.05
which has multi hits<2• residual -0.5mm~0.5mm

160

σ~170μm

140120・Cosmic-ray test is ongoing in KEK Fuji B4・Basic performance test is evaluated.
→ Good performance was obtained so far.
・Trying to increase active channels.
・Development of related sub-system is ongoing.

100
80
60
40
20
0
−2

−1.5

−1

−0.5

0

0.5

1
1.5
2
residual[mm]
residual [mm]613

Read-out Electronics and DAQ
analog+input+from+CDC+48ch

RECBE (semi-copy of Belle-II CDC read-out)

Slit
ASDs
ADCs

Slit
FPGA

Trigger/IF
DAQ/IF+
SiTCP

SFP+slot

Power

Figure 16.1: Block diagram of the StrEcal fast control and trigger systems.
JTAG- 48ch read-out per board- 960MHz TDC and 10bit ADC- 1Gbps SiTCP communication- 128 RECBEs mass production done!
- ﬁrmware development ongoing

FCT board

LVDS

- intermediate board
between trigger andvarious read-out- prototyping done

block diagramof trigger system
Typical Event [3]Decisions andCOMET

Tracking Trigger

Ewen Gillies
COMET
DesignPrinciples- triggering withtrack ﬁnding to
reduce trigger rate
- under development

New Tracking
Techniques
Neighbour-Level
GBDT
Hough
Transform
Track-Level
GBDT

Backup12

14Strawtube Tracker

・Tracker of Straw-tubes- 9.75mm diameter- 20μm thickness- 2-Dimensional conﬁg.
- a station has 2x2 layers
Figure 11.35: Measured detection efficiencies; (Left) Straw single efficiency, (Right) Detection efficiency- 5 stations for Phase-I
as a tracker layer
・ p = 150~200
Figure 11.24:keV/c“ROESTI”: data format
tubes a certain inefficiency should be there, thus the detection efficiency as a tracker layer isalso measured as shown in Figure 11.35 (Right). Even the full-scape prototype has a certain(for 105 MeV/c electron)
11.4.5 Board prototype
inefficiency, high enough efficiency such as ≥95 % is obtained.
With support fromand KEK-Electronics group, a prototype
ROESTI実験準
boar
・Ar:C
2HOpenIt
6=50:50
Phase-I(a)(b)
developed. Currently, the prototype version 3 is under investigation and design wo
gas outlet
Efficiency for Layer : Ar/C2H6=50/50

Efficiency

Efficiency

Efficiency for Straw : Ar/C2H6=50/50

10.8

gas manifold

front-end boards

0.6

1

signal lines

anode
feedthrough

0.8
optical ﬁbre-link
feedthrough0.6

1st straw plane (x1)

0.4straw plane (x2)
2nd

0.4

3rd straw plane (y1)

0.2

0.2

0

1600

1560

4th straw plane (y2)

1700

1800

1900

gas manifold

2000

0

2100
Voltage V

1600

1700

optical ﬁbre-link
feedthroughfront-end boards

1800

1900

2000

2100
Voltage V

anode
feedthroughsignal lines

11

gas inlet

390

1950

200

prototype is ongoing to improve the performance, correct problems discovered usin
3 and optimise the design. Figure 11.25(a) shows the completed prototype version 3
ストローチューブ飛跡検出器
board. As described in the previous section, ROESTI can be connected with several

1.4

a.u.

Drift time (nsec)

Beam

Figure 11.1:180 Schematic view of the straw
tracker; (a) Side view (the straw dimensions is scaled by
1.2160
σx = 143 µm
factor of threeforclarity)and(b)cross-sectionalview of a plane.
1
140

11.1.2

120

0.8

100
0.6

80

Mechanical construction

60

0.4

40

0.2

20

(a)

Mass production(b)

Figure 11.25: Prototype ROESTIROESTI:
read-out
electronics
board;(a) Prototype composed
Version 3,(b) Daisy-chainedboards
The straw-tracker design assumes 9.75 mm diameter conducting
straws,of metalis
Prototype
Straw
Station1
SpatialFigure11.36:
Obtained
X-T
relationand(PET)
its residual distribution,
gasResolution
mixture= Ar/CH (50/50),
Polyethylene
Terephthalate
film
of
20
µm
thickness. The straws
are mounted
on al(developed
for COMET,DRS4)SFP I/O interface as shown in Figure 11.25(b). Intensive testing and R&D work
HV = 1900 V
0-0.5 -0.4 -0.3 -0.2 -0.1 0

0.1 0.2 0.3 0.4 0.5

Distance from wire (cm)0
-1 -0.8 -0.6 -0.4 -0.2 0

0.2 0.4 0.6 0.8

1

2

6

Residual (mm)

ctrons (E) with good resolution, to add redundancy to the electron momentum
t and to provide the ratio E/p for electron identification. The ECAL will also
ional hit position to the electron track trajectory at the location of the ECAL,e tracker-based electron trajectory. The ECAL also provides the trigger signals,
ing with respect to which the electron events are referenced. Independent andurements of the energy of electrons are of critical importance to separate trueæ e≠ N conversion from background tracks that conspire to mimic a signal.

15

Electron Calorimeter (ECAL)
・Energy Measurement for PID- at end-cap of the detector system- combination of 1920 LYSO crystals- 2x2x12 cm (10.5 radiation length)
・Making trigger decision
・Event timing measurement
・ E/E = 5%(for Performance
E = 105 MeV) (1)
ECAL
ECAL(EROS)
Performance (2)・APD + read-out
55

Time Resolution: ch24

Energy Resolution

1.4

The Same DRS4 Chip

quired to have an energy resolution of better than 5% at 105 MeV and a cluster
5.50.8
Momentum scan No.1
on of better than 1 cm. With sufficient crystal granularity, the shower
0.6 topology
Momentum scan No.2
0.4
to discriminate electrons from neutrons and low energy photons. The
crystals5
0.2
ood light yield, and fast response and decay times to reduce pileup. A
schematic
4.5 00 10 20 30 40 50 60 70
AL system is shown in Figure 12.1. Unlike the Mu2e calorimeter, the COMETEnergy in Crystal (MeV)@CM23
not require a central hole to allow the beam pass, since COMET
4 will have
top between the stopping target and ECAL and it has an electron transport
The Others

1

Momentum Scan Sets

3.5

115

3

60

80

100 120 140 160 180
Momentum (MeV/c)

Crystal Timing Resolution

ECALResolution:
Position Resolution
Crystal Time
ch24
9

2
The Same DRS4 Chip
Momentum Scan Set
1.8
The Same Board
mscan1
1.6 8.5
The Others
mscan21.4
1.28
1
0.8 7.5
0.6
0.4
7
0.2
0 6.5
0 10 6020 30
60 14070 16080 90
80 4010050120
180
Energy in Momentum
Crystal (MeV)(Me

Position Resolution (mm)61.2

The Same Board

Time Resolution (nsec)

Time Resolution (nsec)

Energy Resolution (%)

Figure 12.1: A schematic layout of the electron calorimeter system.

resolution~ 4.4%
105 with
MeV/cprototype of ECAL system Energy Compared
performance
test
results
timingsof two @crystalssimilar energy
deposits.
FIG. 69: A vacuum chamber for the prototype ECAL system.

✦χ2 / ndf
Stocastic
Constant
Noise&Leak
Offsetχ2 / ndf
Stocastic
Constant
Noise&Leak
Offset59.41 / 24
0.0002626 ± 0.2619
0.5667 ± 0.007544
4.505 ± 0.1559
4.461 ± 0.1294
38.83 / 25
0.0007392 ± 1.501
0.5461 ± 0.008754
5.016 ± 0.2224
3.804 ± 0.1953

χ2 / ndf
Stocastic
Constant
Noise&Leak
Offset72.17 / 25
0.4976 ± 0.1579
0.125 ± 0.01363
3.961 ± 0.226
4.305 ± 0.1619

StrECAL system
Integration tests of StrECAL system were performed at ELPH in Tohoku Univ.
-

H.Nishiguchi(KEK)

StrECAL Overview

Current Status

COMET CM22-

with prototype of Strawtube Tracker
and prototype of ECAL
operation in vacuum same as real system
100 MeV/c electron beam
successfully triggered by the ECAL
and the electron track was reconstructedwith the Strawtube Tracker.
The prototype of trigger system was tested.

・Strawtube Tracker
the strawtubes were already mass-produced and checked.
- the 1st station of the real detector will be constructed soon (in the winter)
-

・ECAL

in the process to purchase ~500 LYSO crystal for Phase-I- the design work for the real detector is also ongoing
-

16

17

Construction of Hall and Beam-line
COMET Hall next to Hadron Hall

Beam Room(view from Installation Yard)

Installation
Yard
Installation Yard

Experimental Room

Cooling Equipment
will be installed

Installation Door

Experiment Room

Hole for proton beamline

Installation Hatch

Door to Exp. RoomBeam Dump(Iron Blocks will be located)

Beam Room

Beamline Construction (1)COMET Beam-line Wall in Hadron Hall was built

A-Linehigh-p
BL

COMET
BL

18

Construction of Solenoid
Pion capture solenoid system• The delivery of aluminum stabilized

superconductors is being made ( 10
km in 2013, 12 km in 2014, and 8 km
in 2015).
• TS1a coil winding is made by a new
winding machine.
• CS and MS coils were made in 2016

Muon transport solenoid system• The muon transport system (TS2-TS3)

has been constructed and delivered by
Toshiba Co. in 2015

Detector solenoid system• under construction, will be completed
in 2019

TS1a coilwinding

6.

Muon Beam

Figure 26: Overview of the COMET Phase-I Muon Beam line.

The COMET Phase-I muon beam line consists of a section for pion production and capture, a muontransport section and a muon collimation section;. These three elements are descibed in the following
sections. At the ‘downstream’ end of the muon beam line is the detector solenoid. The schematiclayout of the COMET Phase-I muon beam line is shown in Fig. 26.

6.1

Pion Production

The COMET experiment uses negatively-charged low-energy muons, which can be easily stopped ina suitable thin target. The low-energy muons are mostly produced by in-flight decay of low energy
pions. Therefore, the production of low energy pions is of major interest. Conversely, we wish toeliminate high-energy pions, which could potentially cause background events.
6.1.1

Comparison of diﬀerent hadron production codes

In order to study the pion and muon production yields, diﬀerent hadron production simulations werecompared. The comparison of the backward yields of π − and µ− three metres away from the proton
target for diﬀerent hadron production codes is given in Table 3. It is found that there are a factor of 2.5
diﬀerence between diﬀerent hadron production programs. Among them, the QGSP BERT and FTFP BERT
hadron production models have the lowest yield. Therefore, to make a conservative estimation, the
QGSP BERT hadron production model is used to estimate and optimize the muon beam.
Figure 27 shows the momentum distributions for various particles produced by 8 GeV proton bombardment at the location of the end of the pion capture solenoid sections.
6.1.2

Adiabatic transition from high to low magnetic fields

The pions captured at the pion capture system have a broad directional distribution. In order toincrease the acceptance of the muon beamline it is desiarable to make them more parallel to the beamaxis by changing the magnetic field adiabatically. From the Liouville theorem, the volume in the phasespace occupied by the beam particles does not change. Under a solenoidal magnetic field, the product24

R!"#$#%&'()*&
8 GeVMeasurement
test & Extinctio
8 GeV test and Extinction
19•

Extracted p

target and p

8-GeV operation & extinction measurement• Secondary b
By ab4)/$&(,$").-#%&The test was done at J-PARC MR and themeasurement
wasperformedathodoscopewere done at J-PARC in Jan.-Feb., 2018.

COME

Reminder:Available
Two
M
Reminder:Available
Two
Measuremen
K1.8 beam line at Hadron Hall in Jan. - Feb. 2018.
•

NormalEnergyExtraction

30 GeV

COMET
8 GeV

Fast (T2K) Bunched-SX
Slow (Had.) 1b on RCS

Proton leakextraction t

1.2

!s

•

FX

No✤leakage•✤ A• By rejecting
Protonbeam
study
FX obtained:<6
Measurement) thAdva• Good✤ enoug
SXM
Measurement
K4̲rearatleak
Caa(Fast Extraction)✤ B
DEx
SX beam lineH (SlowCa
e

•

Disad
• Both provided
・successfully demonstrated the operation!
Ca
Extinction: (5.4
• Last measurement
carriedout.
•・extinction was measured by FX&SX
both was successfully• Campaign•
2014 @MR
abort, 8 GeV'0%.5(6&/7#8&(,$").-#%9&•Extinctionwasmeasured
by
both
FX
&
SX.
No
•COMET mode •(8Result:
Further improvem- the 1st demonstration of
GeV Bunched-SX)•-6)) byHajimeNISFirst trial of 8 GeV
BunchedSX.
(10double
in
✓
-11
-12
Ext.
=
10
~
10
o
&:()/0"(*(%$/&$);(%&<"#-10- good extinction was < 1.0 x 10
obtained.
External extinction/(.#%6)"B&C()*7D%(&E&F2G2•→ the improvement is expectedSee
by Hajime
solving
thecurrent
issue
Nishiguchi’s talkon Friday
improves
even mor•and increasing the statistics (longer beam time)too&&H,-%.-#%9&• US-Japan coop

20

Software Framework “ICEDUST”

etails).

ICEDUST Offline
Software Suite andEvent Display

oaOfflineDatabase

SimHitMerger

MARS

SimDetectorResponse

SimG4

oaChanInfo
Calibration
Data

Sof
t
war
eandSimulat
ion
GeometryCalibGlobal

Fluka

oaEvent
oaUnpackoaRawEvent
MIDAS datafrom detectors

Key:

Data type

Code usage

Data Flow

Input

Executable

OutputLibrary

ROOT geometry
Data / MC output
EventDisplay

0.04

Input Digitised Czarnecki Spectrum
Original SimG4 Output

0.035
0.03
0.025

ReconGlobal

0.02
0.015
0.01
0.005

AnalysisTools

ComponentofPhase-Imagnet
i
cﬁel
dpar
al
l
el
t
oCDCbeam-axi
s

Phys
i
c
sPr
oc
es
s
es
(
SeeAl
Capt
al
k
t
omor
r
ow)

oaAnalysis
Simple event
data

−3

10

−4

10

−5

10

−6

10

Fi
el
dmaps
TheCOMETExperiment,10Aug2015

0
−2

10

26

Boundmuondec
ay
s
pec
t
r
ai
nGeant4(blue)andt
heor
y(
r
ed)

−7

10

0

10

20

30

40

50

60
70
80
Momentum (MeV/c)

BenKr
i
kl
er
:bek07@i
mper
i
al
.
ac
.
uk

an example for Phase-I* The structure is based on ND280 framework.

The framework “ICEDUST” has almost been ready in 2015.
gure 17.1: An outline of the ICEDUST framework. The structure is largely based on the ND280
amework.
Still need to be implemented more, such as detector response.
The simulation and analysis is/will be studied with ICEDUST now.
events generation is ongoing for more higher statistics study.
7.2. Mass
Data MC
Formats

21

Event Display with ICEDUSTμ-Event Display of “μ-e conversion” generated with ICEDUSTe-20.1.5

22

Net Signal Acceptance

Table 20.2: Breakdown of the µ≠e conversion signal acceptances.

Sensitivity Estimation in COMET Phase-I

Thus the net acceptance for the µ≠e conversion signal of Aµ-e = 0.041 is obtained for T1 = 700
DIO electrons is presented in Section 17.2. In thisns and T2 =1170 ns, where appropriate numbers of the onlinethe
event
selection (see Section 16.1.3),
Pe < 106.0 MeV/c, where Pe is the momentum of electthe offline trackfindingSingle
efficiency(See Section
13.5.1) andAccording
DAQ efficiency
are from
con-DIO e
to this study,(assumed)
the contamination
20.1.6
Event
Sensitivity
event
sensitivity of the µ− N → e− N conversion of 3.1 ×sidered.
The
breakdownoftheacceptance
is
shown
in
Table
20.2.
Signal Acceptance

Signal and DIO(BR=3 the× 10 ) required r
The single event sensitivity (SES) aimed by COMET Phase-I
and≠13
Event selection
Value
Comments
are described. The current upper limit
on gold from SINDRUM-II
is
7
◊
10
[1
SignalOnline event
selectionPhase-I
efficiency
0.9of a factor of 100
Section
16.1.3of COMET
is an improvementon aluminium
over the cDAQ efficiency
0.9
namely,Track finding efficiency
0.99
Section 13.5.1≠
Geometrical acceptanceB(µ+ Track+ Alqualityæ e≠ cuts+ Al) 0.18
= 3 ◊ 10≠15 DIO(as SES) or
Momentum window (Ámom )0.93 103.6≠15MeV/c < Pe <106.0 MeV/c< 7 ◊ 10
(as 90 % C.L. upper limit).
Timing window (Átime )0.3
700 ns < t < 1170 ns
Total
0.041
The SES is given by-15

Counts per 0.1 MeV/c

0.18
0.16
0.14
0.12

0.1

0.08
0.06
0.04
0.02

0
101.5

102

102.5

103

103.5

104

104.5

105
105.5
106
Momentum [MeV/c]

Figure 106: Left: Distributions of the reconstructed µ− N →events. The vertical scale is normalized so that the integrate
Table 20.2: Breakdown of
signalratio
acceptances.
≠ the µ≠e conversion≠
branchingof B(µN → eN ) = 3.1 × 10−15 . Right: The i
signals and DIOofµ-e
the low side of the intµ events
capas a function
gnd
range is 106 MeV/c. The momentum window for signals isthat the DIO contamination would be 0.01 events.
gnd

Signal Sensitivity

B(µ + Al æ e + Al) =

N ·f

1
·f

·A

,

• fcap = 0.61, f = 0.9
where Nµ is the number of muons stopped in the target. The
fraction of capture
17-15• 20.1.6Aμe = 0.041(S.E.S)
SingleEvent Sensitivity
Al ⇥e + whileAl) =the3.3
10 of µ≠e
3 fraction
total16muons on targetB(µfcap =+0.61
is taken,conversion to
16.1.4 Time window for signals• Nμ = 1.5 xstate
10 inmuons
17B(µ⇥ eis taken+ Al)[22].
< 7A 10=-15
the final stateof f + Al= 0.9
0.041(90%C.L.)
is the net signal

gndµ-e
The single event sensitivity (SES) aimedby
COMET
Phase-Iandthe required
running target
timehaveThe
muons
stoppedin the muon-stopping≠15
16
To achieve
SES=3
◊ 10
,onNµgold= 1.5◊ SINDRUM-II
10 ofismuons
needed.
By
using
the
muon
yield
in aluminiumis ≠13about
864 Thenanoseconds.
Th
are Muondescribed.
The
current
upper
limit
from
is
7
◊
10
[1].
goal
intensity
about
0.00052muons
stopped/proton≠4
measured
between the on
protonpulses to(POT)
avoid beam-rela
4.7 ◊ is10an improvementin Section 8.5.,
a totalof numberof protons
targetof 3of COMETof
Phase-Iof a factor
100 onaluminium
overthecurrent
limit,
related backgrounds would come late after the prompt tneeded.
Withtheprotonbeam
currentof
0.4µA,
the measurement
requires aboudays
is needed.
namely, With 0.4 µA, a running time of about 150
fore, thetime window
for search is chosen to start at som

Solenoid
MagnetExtension
toward COMET Phase-II
proton in Phase II
In Phase-I setup-Phase3.2 IkW
proton beam operation
Setup (Proton Beam 3.2 kW)-Muon
90 Transport
degree bymuontransportsolenoida 90 degree
bend Solenoid
detector in a spectrometer solenoid-CDC
CDC
in a spectrometer solenoid

protonstopping target

Phase II Setup (Proton
In Phase-II
setup
Beam 56
kW)

Muon Transport by a
56 kW
proton beam
180 degree bending- new W Proton target
solenoid and a 180(C target in Phase-I)
degree bending- 180 degreetransport
spectrometer
magnet tosolenoid
forthemuon
detectsignal- 180 degree
spectrometer
Straw Tracker& Ecalsolenoid for electron- StrawECAL detector

stopping target-

S-Shape Design in Phase-II

23

24

Phase-II Detector

in vacuum under 1T magnet ﬁeld

ECAL detector

Straw Tracker * # of straw stations is not determined yet.

• 180 curved solenoid for higher momentum resolution in the muon/electron transport• Less dense detectors (Straw Tracker and ECAL in vacuum)

Phase-II Goal :(in a year operation)

B(µ + Al ⇥ e + Al) = 2.6
3.3
B(µ + Al ⇥ e + Al) < 67

10 17 (S.E.S)
10 17(90%C.L.)25

Status of COMET Phase-II
・Development of Phase-I StrawECAL is essentially R&D for Phase-II
Si
mul
a
t
i
onfor
Set
up
・ICEDUST
framework
enablesfeasible
study
Phase-II
Fi
el
dmaps

l
er
:bek07@i
mper
i
al
.
ac
.
uk
ﬁeld map design10for Phase-II BenKriPkhsimulation90setup for Phase-II
as
eI
IOpt
i
mi
s
at
i
on,22Feb.2016
BenKr
i
kl
er
:bek07@

Phas
eI
IOpt
i
mi
s
at
i
on,22Feb.2016

・Working for further foundation in Phase-II, and negotiating with
J-PARC facility for operation schedule for Phase-II26

Summary
・COMET is an experiment search for “μ-e conversion” at J-PARC- aiming improvement the sensitivity x 10,000 better than the past
- staging approach called Phase-I (under construction) / Phase-II
・COMET Phase-I is now under construction- aiming improvement the sensitivity x 100 better than the past
Phase-I Goal :(in 150 days operation)

B(µ + Al ⇥ e + Al) = 3.0
3.3
B(µ + Al ⇥ e + Al) < 77

15 (S.E.S)
10 17
15
10 17

(90%C.L.)- CDC detector for physics search is under commissioning now- the other system is also under construction- will be ready in 2019, stay tuned!
http://comet.kek.jp/
・R&D for COMET Phase-II is underway.
- expecting to start in 202X?, aiming further higher sensitivity