MEG実験用液体Xe scintillation detector の40MeV γ線を用いた性能評価II

東京大学　久松康子

東大素セ、早大理工総研B、阪大理C、高エ研D、BINP-NovosibirskE, INFN-PISAF, PSIG

岩本敏幸、大谷航、小曽根健嗣、菊池順B、久野良孝C、澤田龍、鈴木聡B、寺沢和洋B、道家忠義B、西口創、

服部紘二B、春山富義D、真木晶弘D、真下哲郎、三原智、森俊則、八島純D、山口敦史B、山下了、

山下雅樹B、山田秀衛、吉村浩司D、吉村剛史B、A.A.GrebenukE, D.GrigorievE I.IoudineE, D.NicoloF, S.RittG, G.SignorelliF

2003年9月12日　日本物理学会秋季大会

The current status and schedule of MEG experiment

Development of MEG Experiment Detectors

＊Gamma beam test @PSI

＊Liq. Xe Calorimeter

-Filler study for the Liq. Xe calorimeter

＊COBRA Magnet

Schedule of MEG experiment

Summary

Outline

東大素セ、早大理工総研B、阪大理C、高エ研D、BINP-NovosibirskE, INFN-PISAF, PSIG

久松康子、岩本敏幸、大谷航、小曽根健嗣、菊池順B、久野良孝C、澤田龍、鈴木聡B、寺沢和洋B、道家忠義B、西口創、

服部紘二B、春山富義D、真木晶弘D、真下哲郎、三原智、森俊則、八島純D、山口敦史B、山下了、山本明D、槙田康弘D、

山下雅樹B、山田秀衛、吉村浩司D、吉村剛史B、A.A.GrebenukE, D.GrigorievE I.IoudineE, D.NicoloF, S.RittG, G.SignorelliF

Development of MEG Detectors

Gamma beam test @ PSI

＊π-p→π0 n

　π0(28MeV/c)→γγ

＊π-p→nγ

E(γ)=129MeV

Beam test using the monochromatic gamma beam at PSI πE1 beam line.

*monochromatic γ beam the Energy Calibration

*2γ from the reaction: π0→2γ the absolute timing measurement

kinematics

opening angle (deg)E

nerg

y (M

eV)

50

55

60

65

70

75

80

85

150 155 160 165 170 175 180

Eγ

θ

γ

θ

γ

2 gamma rays emitted back to back in lab. frame: 55 & 84 MeV

δEγ/Eγ < 1% 　　 θ<5°

5°=87mrad=8.7cm@1m

piE1 beam line @ PSIBeam properties:

Max. momentum: 280 [MeV/c]

Solid angle 32[msr]

Momentum acceptance 7.8%

Momentum resolution 0.8 %

Graphite target

Quadruple Magnet

Dipole Magnet

π-flux:

8 * 105 /sec @ 1.6 mA

expected

Vertical & horizontal slits

Experimental Setup

π-- beam

AT

NaI

target

degrader

counter

Trigger : coincidence

2 Counters

& Timing counter

& Liq.Xe

Liq. Xe

Timing Counter

Veto counter

Experimental Setup Cont’dTarget

NaI

Timing Counter

Liq. H2 target

Target cell: 41mm dia. 103mm length

64bars NaI (assembled to form an 8×8array)

63.5×63.5×406 mm3

Position resolution (radial) : σr=4.8 cm @100MeV

Installed in front of NaI detector2plastic scintillators over lapped (5×5cm2)Lead plate (6mm thick)

Prospects

γ beam from π0→2γ will be used to calibrate the Liq. Xe calorimeter in MEG experiment @ piE5, PSI

Resolution required in MEG experiment

Beam Time : Sep. 24th to Dec. 10th

MEG experiment detectorsLiq. Xe calorimeter

Design of liq.Xe calorimeter has almost completed.

The start of the construction: 2004

Subjects to be solved:

Stress, Deformation,

Heat Load, Need of filler

Filler study for the Liq.Xe detector

Some incident photons lose their energy in Liq.Xe, which fills space between the detector wall and PMTs.

To fill the space with materials of long radiation length (“Filler”) will improve the efficiency of this detector.

γ

PMT

vacuum

Signal cable

PMT holder (G10)

Honeycomb (SUS314)

Incident window

Liq.Xe

PMT cover

(acrylic)

Filler studyRequirement for Filler:

Long radiation length

Do not contaminate liq.Xe

The same expansion coefficient as the glass used in Stem

A mixture of Epoxy resin and glass. Filler is attached directly to the PMT.

Cooling Test

PMT

heater

PMTs with Filler are cooled down to 150K.

The temperature of PMT is controlled by Liq.N2, a cold finger (Cu pipe) and a heater.

Now studying…The difference between the thermal expansion rate of epoxy resin and of SUS.

Stress on the PMT cover

COBRA MagnetConstruction finished!

Superconducting coil in cryostat.

potentiometer

Support frame

Compensation coil

COBRA Magnet: Solenoid magnet for positron spectrometer

Gradient field for high rate events

Final Excitation Test completed.On the axisOn the axis＊Magnetic field inside the SC was

measured.

→Good Agreement with the calculation!

＊Fringe field around the photon detector 　region was measured.

→Suppressed by compensation coils.

The Schedule of MEG experiment

Photon detector : Large prototype @PSI background estimation

The construction start in 2004.

COBRA magnet : Shipping to PSI on Sep. 26th

Installation & Engineering runs in piE5

Beam line : Ready by the spring of 2004

Positron tracker : The construction start in 2004.

Electronics & DAQ system : Start assembling in 2004.

All the detectors will be installed in piE5 beam line by 2005.

Engineering runs will start in 2005.

MEG experiment starts at the beginning of 2006.

Summary

Beam test using monochromatic gamma beam starts on Oct. 2nd.

The design of the photon detector has almost completed and now studying details. (Filler problems and so on)

The construction of COBRA Magnet has finished. (Good performance! )

Engineering runs will start in 2005, and MEG experiment at the beginning of 2006.