MEG 2009 現状と展望

MEG 2009 現状と展望

東京大学素粒子物理国際研究センター岩本敏幸　他MEGコラボレーション

日本物理学会 2009 年秋季大会甲南大学岡本キャンパス

Sep.10-13.2009 Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University 2

Contents Detector performance

　　 in 2008

Problems in 2008 and

　　 solutions for 2009 run

DCH

XEC

TC

Upgrade plan

Waveform digitizer (DRS2 to DRS4)

TC fiber readout into trigger

Prospects in 2009

MEG detector performance in 2008

Efficiency %

66 x 91

e+ 30 x 40

Trigger 66

Selection 63x70x903

DAQ 80x93

Calibration Run ~70

Running Time 11.5 (week)

Resolution

E(%) 2.0

T (ps) <80

Position (mm) 5-6

pe+ (%) 0.7, 2, 3.8

Te+ (ps) <60-90

e+(mrad, ,) 18~10

Decay Point (mm) 3-4

Te+ (ps) 150Br(+ e+) < 3.0x10-11 (90% CL)(expected 90%CL sensitivity was 1.3x10-11)

90% signal box


Problems in 2008

Drift chamber (DCH) Operation Discharge problem

Lower efficiency Worse p, ,

Timing counter fiber operation Noisy, couldn’t be used for trigger

worse efficiency for e+ - direction match Liquid xenon calorimeter (XEC) light yield

Light yield: less (~70% of prototype) Because the light yield can be monitored by 17.6MeV CW

calibration, gaseous purification was continued during physics run


Solutions for discharge problem

Investigated weak points for all HV connections

HV soldering spot on PCB, and HV via on PCB are suspicious

DCH discharge reproduced at Lab test finally after many trials !

Solutions New design of PCB

Individual layers with only HV and only GND ( 3 -> 4 layers )

Potting of HV soldering spot with epoxy

After modification

Two chambers with new anode HV pcb into “Aquarium” to see long term operation with He/Ethane inside and pure He outside and nominal HV

16 DC modules are mounted in the support structure inside the helium cabin. Signal check by nominal HV

Stable operation is confirmedfor ~ 5 months

Aquarium

Helium Cabin

Expected performance (DCH)

These MC study will be verified by this year’s Michel data taken with the physics data

•Efficiency• ~ 3 times better by MC

including DCH, DCH-TC matching efficiency

•Resolution• Ee: tail part reduced

• 374keV(60%), 1.06MeV(33%), 2.00MeV(7%) ~ 1.3% (2008)

• ee: 18-10mrad


XEC detector maintenance

Detector maintenance during winter shutdown Fix some (possible) leak positions Fix bad PMTs Gaseous purification for 900L xenon

In July 2009, XEC detector filled with liquid again XEC detector’s been stable since then Light yield monitoring by CW, alpha, CR Liquid purification (~9 times volume circulation)

Gaseous & Liquid purificationGaseouspurification

Liquid purification

1000L liquid storage tank

XEC detector

8 x 250L gasstorage tank

New purifier system

O2 getter cartridge

Developed for LAr use at CERN

H2O also removed by Oxidization-reduction of Cu

New pump speed ~ 180l/h

43 hours operation 7740l circulation

9 times circulation

Light yield in 200917.6MeV of Li(p,)Be, Light yield monitoring

•Higher light yield ~ 40% improved•Consistent with prototype•E might be improved by this light yield increase

X1.4

2008/12 2009/7

waveform

Resolution, energy scale will be measured by 0 calibration

before physics run

decay time ~ 45ns(as expected, ~30ns in last year)

Longer waveformafter purification

2008/92008/122009/7


TC modification Plastic scintillating fiber +

APD ( z measurement ) To provide precise z position

for online trigger New front-end boards design

S/N ~ 8 (noise~40mV) Shorter shaping time for trigger

(250ns -> 20ns) Direction match 66% >90%

z

Direction match

• To get back-to-back e+ events

– direction

• Inner face PMT index with maximum charge in XEC detector (, )

– e+ direction

• TC bar counter ()• TC bar counter charge asymmetry or TC fiber (, or z)

– Direction matching at trigger level

• LUT based on MC

• z reconstruction resolution

– ~7cm at online by using TC bar charge asymmetry

– ~5mm by using TC fiber


Electronics modification Waveform digitizer (DRS2DRS4)

700MHz ~ 5GHz, 8(+1) channels with 1024 storage cells

Eliminate temperature drifts Linearity improved ( 0~1V ) Timing accuracy below 30ps Currently being tested

Trigger Dead time reduction Dynamic range

Some front face PMTs saturated with input range(0-1V) -> (0-2V)

Dedicated trigger Improved separation between ’s and ’s

Direction matching efficiency improvement by using TC APD information


Prospects in 2009

Expected sensitivity(90%CL) in 2009 ~ 2.4x10-12

( ~5 times better)

•Resolution improvement• E

• calibration• light yield

• Ee

• e, e

• Te• stable DC operation

•Background level is still low•Limited by statistics

•Efficiency improvement• e+ (~0.4)• Trigger efficiency (>0.9)• DAQ livetime • Less calibration time• Running Time ~ 8.6 week

•In total, ~ 5 times better


Schedule Other experiment had used E5 beam line until the beginning of Aug. All detectors are ready at Mid. Sep. Calibration run until beg. Oct. Physics run from Oct. ~ 3 months

Aug Sep Oct Nov Dec

Detector installation

0 calibrationPhysics DAQ

Lamb shift experiment


Summary• In 2008 physics run, Br(e)<3x10-11 (90%CL)

• Main problem was DCH discharge, and this problem should be solved in this years run

• Efficiencies, resolutions of all detectors will be improved, and 5 times better statistics than 2008 will be available in 2009.

• All detectors will be ready in mid. Sep., and physics run will be started at Oct. 2009 after a calibration run using 0 in late Sep.

• MEG sensitivity in 2009 will still be limited by statistics, and the expected sensitivity is ~5 times better (2.4x10-12 90%CL). Two more years will be needed to reach a 10-13 sensitivity goal.

素粒子実験領域シンポジウム

主題： Japan-Korea Joint Symposium: Lepton Flavor Violation

Experimental Search for LFV Muon Decay

U-Tokyo ICEPP Mori Toshinori

“Ghost pulse” problem

R

“Ghost pulse”2% @ 2 GHz

“Ghost pulse”2% @ 2 GHz

After sampling a pulse, some residual charge remains in the capacitors on the next turn and can mimic wrong pulses

After sampling a pulse, some residual charge remains in the capacitors on the next turn and can mimic wrong pulses

Solution: Clear before writewrite clear

0 calibration

• -p 0n n

• Back-to-back photons

– 55, 83 MeV

• Opposite detector

– NaI + APD array

• LH2 target

• - beam condition wasn’t the same as + beam ( many e- background )

• This year, 1/4 - beam rate will be used to estimate energy, timing, position resolution as close condition as the +

-

LH2

NaI+APD

XEC

Xe scintillation photon

• Excitation process (fast)

– Xe + Xe* Xe*2 2Xe + h

• Recombination process (slow)

– Xe+ + Xe Xe+2

– Xe+2 + e Xe** + Xe

– Xe** Xe* + heat

– Xe + Xe* Xe*2 2Xe + h

Documents

MEG 2009 現状と展望