Status of the MEG Experiment W. Ootani ICEPP, University of Tokyo for the MEG collaboration.

Status of the MEG Experiment Status of the MEG Experiment

W. OotaniW. OotaniICEPP, University of TokyoICEPP, University of Tokyo

for the MEG collaborationfor the MEG collaboration

Wataru Ootani, Wataru Ootani, ICEPP, University of TokyoICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002NP02, Kyoto, Sep. 27-29 2002

OutlineOutline

• Physics motivations for Physics motivations for the MEG experimentthe MEG experiment• MEG detectorMEG detector• Status of the sub-detectorsStatus of the sub-detectors

Beam lineBeam line Photon detectorPhoton detector Positron spectrometerPositron spectrometer

• MagnetMagnet• Drift chamberDrift chamber• Timing counterTiming counter

Trigger, DAQ, and slow controlTrigger, DAQ, and slow control• SummarySummary


MEGMEG Collaboration Collaboration

A. BaldiniA. Baldini44, A. de Bari, A. de Bari55, L. M. Barkov, L. M. Barkov11, C. Bemporad, C. Bemporad44, P.Cattaneo, P.Cattaneo55, , G. CecchetG. Cecchet55, F. Cei, F. Cei44, T. Doke, T. Doke88, J. Egger, J. Egger66, M.Grassi, M.Grassi44, A. A. Grebenuk, A. A. Grebenuk11, ,

T. HaruyamaT. Haruyama44, P. -R. Kettle, P. -R. Kettle66, B. Khazin, B. Khazin11, J. Kikuchi, J. Kikuchi88, Y. Kuno, Y. Kuno33, A. Maki, A. Maki22, , Y. MakidaY. Makida22, T. Mashimo, T. Mashimo77, S. Mihara, S. Mihara77, T. Mitsuhashi, T. Mitsuhashi77, , T. MoriT. Mori77, D. Nocol, D. Nocolòò44,,

H. NishiguchiH. Nishiguchi77, H. Okada, H. Okada88, W. Ootani, W. Ootani77, K. Ozone, K. Ozone77, R. Pazzi, R. Pazzi44, S. Ritt, S. Ritt66, , T. SaekiT. Saeki77, R. Sawada, R. Sawada77, F. Sergiampietri, F. Sergiampietri44, G. Signorelli, G. Signorelli44, V. P. Smakhtin, V. P. Smakhtin11, ,

S. SuzukiS. Suzuki88, K. Terasawa, K. Terasawa88, A. Yamamoto, A. Yamamoto22, M. Yamashita, M. Yamashita77, , K. YoshimuraK. Yoshimura22, T. Yoshimura, T. Yoshimura88

1 BINP, Novosibirsk, Russia2 KEK, Tsukaba, Japan

3 Osaka University, Osaka, Japan4 INFN, University and Scuola Normale Superiore, Pisa, Italy

5 INFN and University of Pavia, Pavia, Italy6 PSI Villigen, Switzerland

7 University of Tokyo, Tokyo, Japan8 Waseda University, Tokyo, Japan


e e • Event signature Event signature

• Back to backBack to back

• Time coincident Time coincident

• EEe e = = EE= 52.8MeV= 52.8MeV

• Lepton-family-number nonconserving processLepton-family-number nonconserving process• Extremely small branching ratio in the standard model with finite nExtremely small branching ratio in the standard model with finite neutrino mass eutrino mass

ex.) BR(ex.) BR(ee)~)~1010-52-52 for for mm~0.05eV~0.05eV

• Sensitive to physics beyond the standard modelSensitive to physics beyond the standard model

SUSY-GUT, SUSY+νSUSY-GUT, SUSY+νR R , …, …

• Present experimental bound Present experimental bound

BR(μBR(μ ＋＋→→ ee ＋＋ γ) < 1.2 x 10γ) < 1.2 x 10 －－ 11 11 (MEGA experiment, 1999) (MEGA experiment, 1999) • New experiment with a sensitivity of BR~10New experiment with a sensitivity of BR~10-14-14 planned at PSI planned at PSI

μ+

ee++

γ


Physics MotivationsPhysics Motivations

• SU(5) SUSY-GUT predicts BRSU(5) SUSY-GUT predicts BR （（ ee ）＝）＝ 1010-15-15 - 10 - 10-13-13

(SO(10) SUSY-GUT: even larger value 10(SO(10) SUSY-GUT: even larger value 10-13-13 - 10 - 10-11-11))• Small tanSmall tan excluded by LEP SUSY search excluded by LEP SUSY search

J. Hisano et al., Phys. Lett. B391 (1997) 341

Our goal


Physics Motivations, cont’dPhysics Motivations, cont’dAfter the recent SNO measurements...After the recent SNO measurements...

SNO collaboration, Q.R.Ahamd et al., PRL89(2002)010302

SUSY+νSUSY+νRR

Our goal

• Solar Solar meas. strongly favor the LMA. meas. strongly favor the LMA.• Large tanLarge tan large large ee rate rate

J.Hisano and D.Nomura, PRD59(1999)116005J.Hisano and D.Nomura, PRD59(1999)116005


MEG DetectorMEG Detector

• Liquid xenon photon detectorLiquid xenon photon detector

• Positron spectrometer with Positron spectrometer with

gradient magnetic field (COBRA gradient magnetic field (COBRA

spectrometer)spectrometer)

• World’s most intense DC muon World’s most intense DC muon

beam at PSIbeam at PSI

• Sensitivity down to BR~10Sensitivity down to BR~10-14-14

• Engineering/physics run will start Engineering/physics run will start

in 2004in 2004


Sensitivity and BackgroundSensitivity and Background

• Major backgroundsMajor backgrounds

NN=1x10=1x1088/sec, /sec, TT =2.2x10 =2.2x1077sec, sec, /4/4=0.09, =0.09, =0.7,=0.7,ee=0.=0.9595

BR(BR( ＋＋→→ ee ＋＋ ) ~ 0.94 x 10) ~ 0.94 x 10-14-14

• Single event sensitivitySingle event sensitivity

• AccidentalAccidental 　　 CoincidenceCoincidence Michel decay(μMichel decay(μ ＋＋→→ ee ＋＋ ννeeννμμ) ) + random + random γγ

BBaccidental accidental ~ 5 x 10~ 5 x 10-15-15

• Radiative muon decaysRadiative muon decays　　　　 μμ ＋＋→→ ee ＋＋ ννeeννμ μ γγ　　 BBprompt prompt ~ 10~ 10-17-17

ΔΔEEee 0.7% (FWHM)0.7% (FWHM)

ΔΔEEγγ 1.4 – 2.0 % (FWHM)1.4 – 2.0 % (FWHM)

ΔΔeeγγ 12 – 14 mrad(FWHM12 – 14 mrad(FWHM))

ΔΔtteeγγ 0.15 nsec0.15 nsec 　　 (FWHM)(FWHM)

Proposed detector performance

These values could be changed according to the actually achieved performance of the detector.


Beam LineBeam Line• DC muon beam rate above DC muon beam rate above 10108 8 /s/s at at E5 beam lineE5 beam line• Two beam branches (“U” and “Z”)Two beam branches (“U” and “Z”)• Comparative study of the branches Comparative study of the branches is in progress.is in progress.• Positron contamination can be Positron contamination can be reduced by:reduced by: (1) Combination of an energy degrader(1) Combination of an energy degrader and a magnetic selectionand a magnetic selection (2) Wien filter(2) Wien filter

Condition “Z”-branch “U”-branch

No degrader, transmitted to zone

3.6x108+/s

6.0x108e+/s

3.5x108+/s

1.6x109e+/s

Degrader at final focus

2.0x108+/s 3.2x107+/s

m/e ratio at Muon Peak

9 16.5

Decision on the choice of the beam Decision on the choice of the beam branch will be made after the beambranch will be made after the beam tests tests with “U”-branch in Aug.2002 and with “U”-branch in Aug.2002 and with “Z”-branch in Nov.2002with “Z”-branch in Nov.2002

prim

ary

pro

ton

be

am


Liquid Xenon Photon Detector Liquid Xenon Photon Detector

Current designCurrent design Active volume of LXe: ~800 literActive volume of LXe: ~800 liter Scintillation light is collected Scintillation light is collected by ~800 PMTs immersed in LXeby ~800 PMTs immersed in LXe Compact PMT with metal channel dynode sCompact PMT with metal channel dynode s

tructure and quartz windowtructure and quartz window (Hamamatsu R6041Q)(Hamamatsu R6041Q)

• High light yield (75% of NaI(Tl))High light yield (75% of NaI(Tl))• Fast signals Fast signals avoid accidental pileupsavoid accidental pileups• Spatially uniform responseSpatially uniform response no need for segmentationno need for segmentation


Photon Detector PrototypePhoton Detector Prototype

• A total of 120 liter liquid xenon (A total of 120 liter liquid xenon (active volume of 69 literactive volume of 69 liter))• Viewed by Viewed by 240 PMTs240 PMTs• Large enough to test with ~50MeVLarge enough to test with ~50MeV • LEDs and LEDs and sources ( sources (241241Am) implemented for calibrationAm) implemented for calibration


Gamma Beam TestsGamma Beam Tests• Performance test of large prototype using high-energy gamma rays Performance test of large prototype using high-energy gamma rays • Laser Compton backscattering facility at TERAS electron storage ring Laser Compton backscattering facility at TERAS electron storage ring of AIST, Tsukuba, Japanof AIST, Tsukuba, Japan• Gamma-ray beam with energy up to 40MeVGamma-ray beam with energy up to 40MeV• Energy resolution evaluated by spread of Compton edgeEnergy resolution evaluated by spread of Compton edge• Position reconstructed by PMT output distribution with proper collimatorPosition reconstructed by PMT output distribution with proper collimator• Timing reconstructed by averaging arrival timeTiming reconstructed by averaging arrival time• Beam test in Feb. 2002 Beam test in Feb. 2002

Energy spectrum of gamma beamwith 1mm collimator (simulation)


Beam test in Feb. 2002Beam test in Feb. 2002

• Observed amount of light from 40MeV Observed amount of light from 40MeV is smaller than expected. (~10%) is smaller than expected. (~10%)• Strong correlation between the conversion depth and Strong correlation between the conversion depth and NNpepe

• Worse position resolution than expectedWorse position resolution than expected

can be explained by strong light absorption in LXe

Position

22: conversion depth parameter: conversion depth parameter

50<2<55Energy


MC Predictions with AbsorptionMC Predictions with Absorption

Feb02 beam test

MC:monochromatic 40MeV

Energy resolutionEnergy resolution Position resolutionPosition resolution

• MC predictions indicate MC predictions indicate abs abs < 10cm in gamma beam test in Feb. 2002< 10cm in gamma beam test in Feb. 2002• We need We need abs abs > 100cm at least for an energy resolution of a few % order > 100cm at least for an energy resolution of a few % order


Light Absorption in LXeLight Absorption in LXeHH22O, CO, C22HH44, NH, NH33, O, O22 can strongly absorb 175nm scintillation can strongly absorb 175nm scintillation

light from LXe light from LXe Contaminations in LXe? Contaminations in LXe?

Mass spectrum for the remaining gasMass spectrum for the remaining gasin the detector vesselin the detector vessel

He

H2ON2

O2 CO2

Xe


PurificationPurification• New circulatory purification system is installed after the beam testNew circulatory purification system is installed after the beam test in Feb.2002.in Feb.2002.• Xenon vapor is purified in Xenon vapor is purified in Zr-V-Fe getter and Oxisorb filter and Zr-V-Fe getter and Oxisorb filter and recondensed by the refrigerator and LNrecondensed by the refrigerator and LN22 during the operation of during the operation of

the detectorthe detector• Circulation speed 10-12cc liq./minuteCirculation speed 10-12cc liq./minute


Improvement of Light YieldImprovement of Light Yield

Alpha event Alpha event Cosmic ray eventCosmic ray event


Absorption Length EstimationAbsorption Length EstimationAbsorption length is estimated by seeing the absorption of the light fromAbsorption length is estimated by seeing the absorption of the light from the alpha source event and cosmic ray event. the alpha source event and cosmic ray event.

Cosmic ray trigger setupCosmic ray trigger setup4 x alpha source inside 4 x alpha source inside


Absorption Length Estimation, Absorption Length Estimation, cont’dcont’d

Both measurements(CR and Both measurements(CR and ) indicate ) indicate abs abs ~100cm ~100cm

after the purificationafter the purification

Cosmic rayCosmic ray AlphaAlpha


Positron SpectrometerPositron Spectrometer

• Thin superconducting magnet designed to form gradient magnetic fieldThin superconducting magnet designed to form gradient magnetic field• Drift chamber for positron trackingDrift chamber for positron tracking• Scintillation counters for timing measurementScintillation counters for timing measurement

COBRA spectrometerCOBRA spectrometer


Concept of COBRA SpectrometerConcept of COBRA Spectrometer

Gradient field

Gradient field

Uniform field

Uniform field

COBRA : COnstant Bending RAdius• Constant bending radius independent of emission anglesConstant bending radius independent of emission angles

• Low energy positrons quickly swept out Low energy positrons quickly swept out


MagnetMagnet• Five coils with three different diameter to form Five coils with three different diameter to form gradient fieldgradient field• BBcc = 1.26T, B = 1.26T, Bz=1.25mz=1.25m=0.49T@ operating current = 359A=0.49T@ operating current = 359A• Compensation coils to suppress the residual field around the LXe detectorCompensation coils to suppress the residual field around the LXe detector down to ~50Gaussdown to ~50Gauss• High-strength aluminum stabilized superconductor High-strength aluminum stabilized superconductor thin superconducting coil: thin superconducting coil: 0.20.2XX00


Construction of the MagnetConstruction of the Magnet

Central coil

• Magnet design was finalized after detailed mechanical Magnet design was finalized after detailed mechanical calculations and related experimental tests.calculations and related experimental tests.• Winding of the cable is in progress @ Toshiba.Winding of the cable is in progress @ Toshiba.• Excitation test for the central part of the magnetExcitation test for the central part of the magnet will be performed in October 2002.will be performed in October 2002.

Central coil Gradient coil

Compensation coil

Winding of the central coil


Positron TrackerPositron Tracker

• 17 chamber sectors aligned radially 17 chamber sectors aligned radially with 10°intervalswith 10°intervals• Two staggered arrays of drift cellsTwo staggered arrays of drift cells• Chamber gas: He-CChamber gas: He-C22HH66 mixture mixture• Vernier pattern on the cathode foil Vernier pattern on the cathode foil to determine z-positionto determine z-position


First Prototype of the ChamberFirst Prototype of the Chamber

Resolution(Resolution())

Drift time measurementDrift time measurement 100-150100-150mm

Vernier cathod measurementVernier cathod measurement 425425mm

Charge division measurementCharge division measurement 2cm2cm

Drift velocity and drift timeDrift velocity and drift time 4-12ns4-12ns

Sr-90Sr-90


Chambers System R&D in PSIChambers System R&D in PSI• Two prototypes are under construction at PSI.Two prototypes are under construction at PSI.

• “ “Double cathode” test chamberDouble cathode” test chamber• Two separated double-strip cathodes for Two separated double-strip cathodes for

each chamber layereach chamber layer homogeneous position sensitivityhomogeneous position sensitivity

• Test in 1 Tesla magnetic fieldTest in 1 Tesla magnetic field• “ “Charge division” test chamberCharge division” test chamber

• Charge division testCharge division test• 1m-long W(330W/m) or Steel(1200W/m) 1m-long W(330W/m) or Steel(1200W/m)

• Supporting system is also under development.Supporting system is also under development.


Timing CounterTiming Counter

• Two layers of scintillator hodoscopes placed at right angles with each otherTwo layers of scintillator hodoscopes placed at right angles with each other Outer: Outer: timing measurementtiming measurement Inner: Inner: additional trigger informationadditional trigger information• Goal Goal timetime~ 50psec~ 50psec


Timing Counter PrototypeTiming Counter PrototypeCORTESCORTES: Timing counter test facility with cosmic rays at INFN-Pisa: Timing counter test facility with cosmic rays at INFN-Pisa

• Scintillator bar (5cm x t1cm x 100cm long)• Telescope of 8 x MSGC• Measured resolutions time~60psec independent of incident position• time improves as ~1/√Npe use thicker counter ~t2cm


Trigger ElectronicsTrigger Electronics

• Beam rate 10Beam rate 1088 s s-1-1

• Fast LXe energy sum >45MeV 2x10Fast LXe energy sum >45MeV 2x1033 s s-1-1

• interaction pointinteraction point• ee++ hit point in timing counter hit point in timing counter• Time correlation Time correlation -e-e++ 200 s 200 s-1-1

• Angular correlation Angular correlation 20 s20 s-1-1

• Design and simulation of type1 board completedDesign and simulation of type1 board completed

• Prototype board delivered in Pisa by this fallPrototype board delivered in Pisa by this fall

Trigger system structure


Slow ControlSlow Control• New field bus system under development for a reliable control of New field bus system under development for a reliable control of cryogenics of LXe detector, superconducting magnet, cryogenics of LXe detector, superconducting magnet, high voltage supply high voltage supply • Low cost (typ. 20 US$ per node)Low cost (typ. 20 US$ per node)• Several prototypes have been built and tested at PSISeveral prototypes have been built and tested at PSI• SeeSee http://midas.psi.ch/mscb


SummarySummary

• R&D work on the sub-detectors for the MEG experiment are going well.R&D work on the sub-detectors for the MEG experiment are going well.• Performance of the LXe photon detector prototype is improving thanks toPerformance of the LXe photon detector prototype is improving thanks to

the improvement of the light yield.the improvement of the light yield.• A beam test of the photon detector prototype with the purified xenonA beam test of the photon detector prototype with the purified xenon

will be performed in Oct. 2002.will be performed in Oct. 2002.• Beam line tuning with the COBRA magnet and assembly of Beam line tuning with the COBRA magnet and assembly of

the sub-detectors will start in 2003.the sub-detectors will start in 2003.• Engineering run will start in 2004.Engineering run will start in 2004.

Updated status can be seen at three mirrored sites:Updated status can be seen at three mirrored sites: http://meg.icepp.s.u-tokyo.ac.jp/ http://meg.psi.ch/ http://meg.pi.infn.it/

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Status of the MEG Experiment W. Ootani ICEPP, University of Tokyo for the MEG collaboration.

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