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Mar.20-23.2010 Toshiyuki Iwamoto (ICEPP) JPS 2010 Spring meeting, Okayama University

MEGQeK Run2009

MEG

Contents QeK search & MEGExperiment MEG Run2009 and detectorperformance in 2009 Analysis procedure & the current status Prospects in 2010

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Background

Accidental background is our main background

Q eK searchSignal

Positive Q decay at rest

Clear two body kinematics

Back to back (180)

EeEK=52.8MeV Coincident (Te=TK)

KKK HH.HH eeeacc tEEB w22 )()(

K BGe+ BG

Michel positron Random K

.etcKKpee

,KRRQ peRRQ pe

Good detector performance is essentialHigh rate e+ measurement with intense Q beam

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MEGExperimentTarget sensitivity : Br(QeK)~10-13

Current best limit : 1.2x10-11by MEGA experiment

Worlds most intensecontinuous muon beam

MEG detector1.3MW PSI Proton cyclotron

Physics DAQ has started since 2008

The result of Run2008 : Br(Q+e+K)2.8x10-11(90%C.L.)

(Sensitivity was 1.3x10-11)(to be published, cf. J.Adam et al,MEGCollaboration, arXiv:0908.2594)

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MEG Run2009 Full DCH modules worked well LXe light yield as good as expected by prototype

Physics run condition

6.3Hz trigger rate

38TB in total including calibration data

Physics run2009 was shorter than run2008

Apr

Jul

Oct

Jan

2010

PSI accelerator shutdown

Other experimentDCH modificationMaintenance work for MEG

Detector setupCalibrationWaveform digitizer update

Physics run ( 2 months )

PSI accelerator shutdown

2.9x107 Q/s beam intensity

In total, 6.5x1013 Q stoppedon target

Three daysmaintenance

Run2009

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Positron spectrometer Discharge problem of positron tracker (drift chamber, DCH) happened in 2008.The

problem was finally figured out in HV distribution cards after intensive works

All DCHs were repaired before physics DAQ in 2009, and the detection efficiency(14% 40%) and performance of DCH was much improved.

Hit map 2008

2009

Ue

1811mrad

Je

108mrad

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Photon Detector (XEC

) Light yield of liquid xenon in 2008 was improving during physics run by purification Gaseous purification was done for all xenon before physics run in 2009, and the

light yield in 2009 was as good as expected by our prototype

Light yield in 2009 had been stable during physics run without any purification.

Run2008gas&liquidpurification Run2009

Light Yield Energy resolution

Calibration is not finalized yet in 2009, butcomparable resolution is already achieved

signal

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2009 Detectorperformance2008 2009

(preliminary)

Gamma Energy (%) 2.0 (w>2cm)

Gamma Timing (psec) 80 >67

Gamma Position (mm) 5(u,v)/6(w)

Gamma Efficiency (%) 63

e+ Timing (psec)

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Analysis procedure Preselection: ~20% of all events

Blind analysis to avoid any bias

TeK(-1ns

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Maximum likelihood fitting

PDF preparation (S, R, B) : PDF for (QeK, RMD, Background)

Product ofPDFs for the five observables

(EK, Ee, teK, UeK and JeK) Fitting parameters (NBG, NRMD, NSignal)

All figures shown here are run2008 results

All PDFs are being prepared now for run2009

),(!

exp),,(

1

BN

NR

N

NS

N

N

N

NNNNL BGRMD

sigN

iobs

NN

BGRMDsig

obsobs

!!

Blue: AllPink: BGRed: RDGreen: Signal

EKE

e

TeK

UeK

JeK

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Normalization

Count the number of detectedMichel positrons (Michel trigger) NeRRobtained simultaneously with

the signal (MEG trigger)

The upper limit on BR(Q+e+K) iscalculated by normalizing Nsig tothe NeRR

Independent of instantaneousbeam rate and insensitive topositron acceptance andefficiency

KKKKK II

I

I

IKQ

e

g

e

CH

e

CH

vev

TC

e

TC

vev

trig

e

trig

vev

E

vev

vev

sig

AA

A

P

fe

11)( vvvvvv!p

Theory

Resolution

Selectionefficiency

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Run2009 PDF preparation

We are still calibrating the detector and optimizing algorithms

Several times, re-processing for preselected events will be done after certainimprovement

Hopefully in June 2010, well open the blind box, and do the final analysis

Target: publish the result at this summer conference

EK sideband data PDF forEK BG

Ee data PDF forEe BG

TeK data PDF for TeK signal

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Run 2010

Detector performance should be improved by reconstructionalgorithm and calibration methods

Positron beam ( efficiency, resolution )

DCH noise removal ( resolution )

Gamma energy (1.5%W at the best point)

Trigger efficiency ( TC fiber counter)

Optimization of beam stopping position

Data statistics in 2010 will be 11 times higher than 2008 ( 6months data taking ), and the sensitivity is estimated to be

1.3x10-12.

Three years data taking (2010-2012) will enable us to reach thesensitivity of~10-13 level

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Prospects in 20102008 2009 (preliminary) 2010 (preliminary)

Gamma Energy (%) 2.0 (w>2cm) 1.5 (w>2cm)

Gamma Timing (psec) 80 >67 68

Gamma Position (mm) 5(u,v)/6(w)

Gamma Efficiency (%) 63

e+ Timing (psec)

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Optimization of beam stopping

position

Degrader thickness (300Qm 200Qm) in 2009 to match6% air contamination in COBRA by means of MCstudy.

Strong asymmetry was observed by TCupstream/downstream hit map

Beam test for optimization of the degrader is planned

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TC modification

Plastic scintillating fiber +APD ( z measurement )

To provide precise z positionfor online trigger

New front-end boards design

S/N ~ 8 (noise~40mV)

Shorter shaping time for trigger(250ns -> 20ns)

TC bars (J

measurement )

207Bi on TC bar center

Better z position calibration

zJ

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Electronics modification

Waveform digitizer (DRS2DRS4)

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

Improved separation between Es and Ks

Direction matching efficiency improvement byusing TC APD information

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PMT gain shift

Problem in photo

cathode production

stage Might be different

mixture at certain

period, too much

alkali?

R 8 Gain Shift vs SKB

0.8

0.8

0.

0.

1

1.0

1.1

1.1

1.2

1

120

223

3

3

1

3

8

3

1032

1112

12

8

13

1

1

3

1

01

1

3

1

1

1

83

18

1

1

02

1

8

Serial No.

GainShift

2

3

8

SKB

GainShift

SKB

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Ghost pulse problemR

Ghost pulse2% @ 2 GHz

After sampling a pulse, some residual chargeremains in the capacitors on the next turn andcan mimic wrong pulses

Solution: Clear before write

write clear

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UeK

, JeK

Opening angle resolution

combination of

positron angle resolution

target position resolution

photon detector position

2008 results

Documents

Nestle - Zaka (40)