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The The MEG ExperimentMEG Experiment at PSI: at PSI: a sensitive searcha sensitive search forfor
µ µ eeγγ decaydecay
Fabrizio CeiFabrizio CeiINFNINFN and and University of PisaUniversity of Pisa
XV XV Incontri sulla Fisica delle Alte EnergieIncontri sulla Fisica delle Alte Energie
LecceLecce, 23, 23--25 April 200325 April 2003
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 22
OutlineOutlinePhysics motivations:Physics motivations:
SUSY indications;SUSY indications;Connection with neutrino oscillations.Connection with neutrino oscillations.
The The µµ →→ eeγγ signature:signature:Signal & Background.Signal & Background.
The experimental The experimental setupsetup::The The muonmuon beam;beam;The positron spectrometer;The positron spectrometer;The timing counter;The timing counter;The Liquid Xenon e.m. calorimeter;The Liquid Xenon e.m. calorimeter;Trigger & Electronics.Trigger & Electronics.
Conclusions:Conclusions:Sensitivity;Sensitivity;Time profile.Time profile.
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 33
Physics MotivationsPhysics MotivationsIn theIn the Standard ModelStandard Model withwith massivemassive DiracDirac neutrinos neutrinos Lepton Lepton Flavour Violation processesFlavour Violation processes (as(as µ µ →→ eγγ, , τ τ →→ eeγγ, , µ µ →→ eeeeee, , µ µ →→ ee) ) are predicted are predicted atat immeasurably small levelsimmeasurably small levels ..
However,However, Super Symmetric TheoriesSuper Symmetric Theories predict predict such processessuch processesatat much more reasonable ratesmuch more reasonable rates..
Since theSince the SM background is negligible, SM background is negligible, processes like processes like µ µ →→ eγγareare clear evidences for Super Symmetryclear evidences for Super Symmetry..
Problem:Problem: are such rates are such rates experimentally observableexperimentally observable ??
( )5010−~
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 44
SUSY IndicationsSUSY IndicationsLFV processes especially sensitive toLFV processes especially sensitive to SSM grand unified SSM grand unified theories (SUSYtheories (SUSY--GUT)GUT)..
LFV induced by LFV induced by finite finite sleptonslepton mixingmixingthrough through radiativeradiative correctionscorrections..
Some predictions:Some predictions:SUSY SU(5) SUSY SU(5) BR BR ((µ µ →→ eeγγ)) ≈≈ 1010--14 14 ÷÷ 1010--1313
SUSY SSUSY SOO((1010) ) BRBRSO(10)SO(10) ≈≈ 100 100 BRBRSU(5)SU(5)
(R. (R. BarbieriBarbieri et al.,et al., Phys. Phys. Lett. Lett. BB338338(199(19944) 21) 2122
R. R. BarbieriBarbieri et al.,et al., NuclNucl. Phys. . Phys. B445B445(1995) 215)(1995) 215)
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 55
Predictions of Predictions of µ µ →→ eeγγ BRBR in in SU(5)SU(5) ModelsModels
Experimental Bound
Goal of MEG Experiment
J.J. HisanoHisano et al.et al., , Phys.Phys. LettLett. . B391B391 (1997) 341(1997) 341
Small (< 10) tan Small (< 10) tan ββ valuesvaluesare are highly disfavouredhighly disfavoured by by recent combined recent combined LEP dataLEP data..
(ALEPH, DELPHI, L3 & OPAL (ALEPH, DELPHI, L3 & OPAL Collaborations, hepCollaborations, hep--ex/0107030)ex/0107030)
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 66
Connection with Connection with νν--oscillationsoscillations
log(tan θ)
log(
∆m /
eV )
2
2
2
90% CL
95% CL
99% CL
99.73% CL
LMA
LOW
(b)
-12
-11
-10
-9
-8
-7
-6
-5
-4
-4 -3 -2 -1 0 1
10
Experimentalbound
MSW
LM
A
-1-2-3 11010
MSW small angle
MSW large anglesmall mass
Just so
MSW large angle
sin θ22
∆m
2(e
V )2
µe
γ
νR2
)B
r(
M (GeV)
10
10
10
10
10
10
10
10
-3
-4
-5
-6
-7
-8
-9
-10
10
10
10
10
10
10
10
10
10
10 10 10
-11
-8
-9
-10
-11
-12
-13
-14
-15
12 13 14
MSW
LO
W
Vacuu
m
Our goalOur goal
Experimental boundExperimental boundLargely favouredLargely favouredand confirmed byand confirmed by KamlandKamland
Additional contributionAdditional contribution toto sleptonslepton mixingmixing fromfrom VV2121, matrix element , matrix element responsible responsible forfor solar neutrino deficitsolar neutrino deficit. . ((J.J. HisanoHisano & N. Nomura, Phys. Rev. & N. Nomura, Phys. Rev. D59D59 (1999) 116005)(1999) 116005)
All All solar solar νν experimentsexperiments combinedcombined
tan(tan(ββ) = 30) = 30OO
tan(tan(ββ) = 0) = 0OO
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 77
Previous Previous µµ →→ eeγγ Searches Searches
MEGMEG~~ 1010--1313~2005~2005PSIPSI
MEGAMEGA< 1.2 < 1.2 ×× 1010--111119991999LANLLANL
Crystal BoxCrystal Box< 4.9 < 4.9 ×× 1010--111119861986LANLLANL
W.W.W.W. KinnisonKinnison et al.et al.< 1.7 < 1.7 ×× 1010--101019791979LANLLANL
P.P. DepommierDepommier et al.et al.< 3.6 < 3.6 ×× 1010--9919771977TRIUMFTRIUMF
A. VanA. Van der Schaafder Schaaf et al.et al.< 1.0 < 1.0 ×× 1010--9919771977PSI PSI
Experiment or AuthorsExperiment or AuthorsUpper limitUpper limitYearYearLab.Lab.Other LFV searchesOther LFV searches
The The MEG experimentMEG experiment aims to aims to gain two orders gain two orders of magnitudeof magnitude in in thethe upper limitupper limit (not a simple (not a simple experimental challenge!).experimental challenge!). MEGMEG
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 88
The MEG CollaborationThe MEG CollaborationINFN & INFN & LecceLecce UniversityUniversity G. Cataldi, C. Chiri, P. Creti, F. Grancagnolo, M. G. Cataldi, C. Chiri, P. Creti, F. Grancagnolo, M. Panareo, S. SpagnoloPanareo, S. SpagnoloINFN & Pisa UniversityINFN & Pisa University A. Baldini*A. Baldini*, C. Bemporad, F.Cei, M.Grassi, F. Morsani, , C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. SignoreD. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. SignorellilliINFN & PINFN & Paviaavia UniversityUniversity A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. RossellaRossellaINFN & INFN & GenovaGenova UniversityUniversity S. Dussoni, F. Gatti, D. Pergolesi, R. ValleS. Dussoni, F. Gatti, D. Pergolesi, R. ValleINFN Roma I INFN Roma I D. ZanelloD. Zanello
ICEPP, University of TokyoICEPP, University of Tokyo T. Mashimo, S. Mihara, T. Mitsuhashi, T. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori*T. Mori*, , H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. YamaH. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. YamashitashitaKEK, TsukubaKEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. YoshimuraT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. YoshimuraOsakaOsaka UniversityUniversity Y. KunoY. KunoWasedaWaseda UniversityUniversity T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. YoshimuraYamashita, T. Yoshimura
Budker Budker Institute, Institute, NovosibirskNovosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. RyskulovKhazin, N.M. Ryskulov
PSI, PSI, VilligenVilligen J. Egger, P. Kettle, M. Hildebrandt, S. RittJ. Egger, P. Kettle, M. Hildebrandt, S. Ritt
** SpokepersonsSpokepersons
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 99
Signal and BackgroundSignal and Background
ee++ µµ++ γγ
θθeeγγ = 180°= 180°EEee == EEγγ == 52.8 MeV52.8 MeV
ttee = = ttγγ
SignalSignalµµ →→ ee γγ
BackgroundBackground““Prompt”Prompt”µ µ → e γ ν ν
((muon radiative decaymuon radiative decay))
ee++ µµ++ γγνν
νν
““Accidental”Accidental”µµ →→ ee νν νν
µµ →→ ee γγ ν νν νee ee →→ γγ γγ
eZ eZ →→ eZeZ γγ
ee++ µµ++ νννν
γγ
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1010
Experimental StrategyExperimental Strategy
Use a Use a highhigh--intensity intensity muonmuon beambeam and and µµ--decay at restdecay at rest;;Measure Measure γγ time, energy time, energy and angleand angle by using by using aa fast fast & high& high--resolution e.m. resolution e.m. calorimetercalorimeter;;Measure Measure ee++ momentummomentumby using a by using a highhigh--resolution spectrometerresolution spectrometer;;Measure Measure ee++ timetime by using by using fast countersfast counters ((scintillatorscintillatorbarsbars););Use a Use a trigger schemetrigger schemebased on the based on the ee++--γγcoincidencecoincidence..
1m
e+
Liq. Xe ScintillationDetector
γ
Drift Chamber
Liq. Xe ScintillationDetector
e+
γ
Timing Counter
Stopping TargetThin Superconducting CoilMuon Beam
Drift Chamber
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1111
A simulated eventA simulated event
52.852.8 MeVMeV photonphoton
52.852.8 MeVMeV positronpositron
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1212
Required PerformancesRequired Performances
1 x 101 x 10--1313
1.2 x 101.2 x 10--1111
4.9 x 104.9 x 10--1111
1.7 x 101.7 x 10--1010
1 x 101 x 10--99
3.6 x 103.6 x 10--99
BRBR(90% CL)(90% CL)
20052005
1999199919861986
1979197919771977
19771977
YearYear
1001002.5 x 102.5 x 107719190.150.15440.80.8MEGMEG
(6..7)(6..7)2.5 x 102.5 x 108817171.61.64.54.51.21.2MEGAMEGA(6..9)(6..9)4 x 104 x 105587871.31.38888Crystal BoxCrystal Box
6.46.42.4 x 102.4 x 105537371.91.9888.88.8LANLLANL1001002 x 102 x 1055--6.76.78.78.71010TRIUMFTRIUMF
1001005 x 105 x 1055--1.41.49.39.38.78.7SIN SIN
Duty Duty cycle (%)cycle (%)
Stop rate Stop rate (s(s--11))
∆θ∆θeeγγ
((mradmrad))∆∆tteeγγ(ns)(ns)
∆∆EEγγ //EEγγ
(%)(%)∆∆EEee//EEee
(%)(%)Exp./LabExp./Lab
Experimental sensitivity limited by Experimental sensitivity limited by spillspill--in of backgroundin of background (especially accidental) (especially accidental) into signal regioninto signal region high resolution measurements are neededhigh resolution measurements are needed. The accidental . The accidental BR isBR is
To obtainTo obtain BR BR ((µ µ →→ eeγγ)) ≈≈ 1010--1313 we must havewe must have BRBRaccacc ≈≈ 33••1010--1414 and this requires:and this requires:eγeγγeµacc ∆t∆θ∆E∆ERBR ××××∝ 22
FWHMFWHM
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1313
Detector BuildingDetector BuildingSwitzerlandSwitzerlandDrift Drift ChambersChambers,,Readout & DAQReadout & DAQ
JapanJapanLXeLXe Calorimeter,Calorimeter,SuperconductingSuperconductingSolenoidSolenoid
RussiaRussiaManpower,Manpower,MuonsMuons transport transport solenoidsolenoid
ItalyItalyee++ counter (counter (GeGe ++ PvPv), ), Trigger (Pi, Le),Trigger (Pi, Le),Splitter (Le),Splitter (Le),LXeLXe Calorimeter (Pi, Le)Calorimeter (Pi, Le)
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1414
The Paul The Paul ScherrerScherrer InstituteInstitute
Experimental HallExperimental Hall
The The most powerful machinemost powerful machinein the world;in the world;Proton energyProton energy 590 590 MeVMeV;;Nominal operation currentNominal operation current 1.8 1.8 mAmA
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1515
The The MuonMuon BeamBeam
Primary Primary proton beamproton beam
ItIt existsexists;;It providesIt provides continuouscontinuous >> 10108 8 µµ++/s/s (with (with ee++ contaminationcontamination) on ) on 5x5 5x5 mmmm22;;Two separate configurationsTwo separate configurations of theof the ππE5E5 beam linebeam line ((UU & & ZZ););MuonMuon momentummomentum 2929 MeVMeV/c/c..
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1616
Beam Line TestsBeam Line Tests
Goal: Goal: optimizeoptimize the beam elementsthe beam elements in order in order
to achieve:to achieve:
a)a) a a good good µµ/e separation/e separation mass selection mass selection device (device (WienWien filterfilter); );
b) a b) a good couplinggood coupling between between beam and beam and spectrometerspectrometer solenoidal solenoidal magnetmagnet;;
c) a c) a high intensityhigh intensity of of stopping stopping muonsmuons in a in a spot spot ≈≈ 5x5 mm5x5 mm22 degraderdegrader to to reduce reduce the the muonmuon momentummomentum before a before a 150 150 µµm m targettarget..
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1717
ResultsResultsRRµµ (total)(total)
RRµµ (after filter)(after filter)
µµ/e /e separationseparation
Spot size Spot size σV≈ 6.5 mm, σH≈ 5.5 mm (U)(U)
s/10branch) (Z 5.9branch) (U 3.7 7 +×
µ
/s µ+× 8103.1
branch) (Z 7branch) (U 11
σσ
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1818
The Positron SpectrometerThe Positron Spectrometer
Gradient fieldGradient field Uniform fieldUniform field
Gradient fieldGradient field Uniform fieldUniform field
COCOnstantnstant BBendingending RARAdiusdius ((COBRACOBRA) spectrometer) spectrometer• Constant bending radiusConstant bending radius independent of emission anglesindependent of emission angles
• HighHigh ppTT positronspositrons quickly swept outquickly swept out
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 1919
Magnetic Field Magnetic Field
Longitudinal Profile Longitudinal Profile (R = 0)(R = 0)
Radial Profile Radial Profile
Needed < 50 GNeeded < 50 G: : OKOK)
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2020
Solenoids and CoilsSolenoids and Coils
BBcc == 1.26 T1.26 T current =current = 359 A359 A;;Five coilsFive coils withwith three different diametersthree different diameters;;Compensation coilsCompensation coils to to suppress the stray fieldsuppress the stray field around the around the Liquid XenonLiquid Xenon detector;detector;HighHigh--strength aluminium stabilized superconductor strength aluminium stabilized superconductor
⇒⇒ thin magnetthin magnet ((1.46 cm Aluminium1.46 cm Aluminium, , 0.2 X0.2 X00););““CrashCrash”” TestsTests completed;completed;WindingWinding completed @completed @TOSHIBATOSHIBA;;Magnet readyMagnet ready to be shipped atto be shipped at PSIPSI within this yearwithin this year..
Central coil
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2121
Positron TrackerPositron Tracker
17 chamber sectors17 chamber sectors alignedaligned radiallyradially with with 1010°° intervalsintervals and and 20 wires20 wires each;each;Two staggered arraysTwo staggered arrays of drift cells;of drift cells;Chamber gas: Chamber gas: HeHe--CC22HH66 mixturemixture (50/50)(50/50) to to reduce reduce multiple scatteringmultiple scattering;;VernierVernier patternpattern made of made of 15 15 µµmm kaptonkapton foilsfoils to to measure zmeasure z--positionposition byby charge divisioncharge division..
σσ(X,Y) ~ 200 (X,Y) ~ 200 µµmm (drift time)(drift time);; σσ(Z) ~ 300 (Z) ~ 300 µµmm;; σσ(t) ~ 10 ns (t) ~ 10 ns
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2222
Drift Chambers R & DDrift Chambers R & D
• FullFull--size prototypesize prototype @ @ PSIPSI; test in ; test in NNovember ovember ((cosmic cosmic muonsmuons & & 9090Sr sourceSr source, , magnetic fieldmagnetic field););
•• Improved Improved verniervernier stripsstrips structurestructure ((uniform resolutionuniform resolution););•• Summary of Summary of Drift Chamber simulationDrift Chamber simulation..
÷=
÷=
÷=
+
++
mm..xmrad
%..P/P
orig
e
ee
5212
129
9070
∆
θ∆
∆
±=±=
mm
Z
R
µσµσ
74251093First results with a First results with a smallsmall--size prototypesize prototype
@@ Tokyo universityTokyo university ((9090Sr sourceSr source, , no magnetic fieldno magnetic field) )
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2323
Positron Timing CounterPositron Timing Counter
BC404BC404 scintillatorscintillator
Two layersTwo layers of of scintillation countersscintillation counters read byread by PMTsPMTs at at right anglesright angles with each other.with each other.OuterOuter: mainly : mainly timing measurementtiming measurement InnerInner: mainly : mainly trigger informationtrigger informationGoal: Goal: timing resolutiontiming resolution 100100 psps FWHMFWHM
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2424
Timing Counter R & DTiming Counter R & DTiming resolutionTiming resolution measurement:measurement: COCOsmicsmic RRayay TESTEStt Facility Facility ((CORTESCORTES))
4 small counters4 small counters + + 8 MSGC8 MSGC + + 11 scintillatorscintillator barbar ((1 cm thick1 cm thick))
σσt t improves as ~improves as ~1/1/√√NNpepe ⇒⇒ 2 cm thick2 cm thickto get to get 100100 psps FWHMFWHM resolutionresolution
Measured resolutionMeasured resolution
psFWHM
pst
140
60
≈⇓
≈σ
New designNew design in progress; expected in progress; expected full simulationfull simulation of of geometrygeometry and and light collectionlight collectionand and prototype testsprototype tests in in October/NovemberOctober/November; ; final design and building in 2004final design and building in 2004. .
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2525
Liquid Xenon CalorimeterLiquid Xenon Calorimeter
Liq. Xe
H.V.
Vacuumfor thermal insulation
Al Honeycombwindow
PMT
Refrigerator
Cooling pipe
Signals
fillerPlastic
1.5m
Liquid Xenon propertiesLiquid Xenon properties
800 l800 l of of Liquid XenonLiquid Xenon equipped withequipped with ≈≈ 800 800 PMTsPMTs;;Homogeneous detectorHomogeneous detector;;OnlyOnly scintillationscintillation lightlight;;LargeLarge light yield light yield (~ (~ NaINaI))..
Density 2.95 g/cm3Boiling and melting points 165 K, 161 KEnergy per scintillation photon 24 eVRadiation length 2.77 cmDecay time 4.2 ns, 22 ns, 45 nsScintillation light wave length 175 nmScintillation light absorption length > 100 cmAttenuation length (Rayleigh scattering) 30 cmRefractive index 1.74
Experimental Experimental checkcheck
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2626
LXeLXe Calorimeter PerformancesCalorimeter Performances
Full MC simulationFull MC simulation of of Liquid XenonLiquid Xenon behaviour and behaviour and calorimeter responsecalorimeter response..PositionPosition resolutionresolution::
corresponding to: corresponding to:
angular resolutionangular resolution(practically independent of (practically independent of light absorption lengthlight absorption length).).ZZ--coordinate resolutioncoordinate resolution (depth of (depth of interaction pointinteraction point; important for ; important for timing timing resolutionresolution preliminary measurements laterpreliminary measurements later):):
Energy resolutionEnergy resolution strongly depends on strongly depends on optical propertiesoptical properties of of Liquid XenonLiquid Xenon
reconstruction algorithmsreconstruction algorithms needed toneeded to correct correct for for non homogeneitiesnon homogeneities. .
mm 5≈≈ yx σσ
mrad 756 ÷≈≈ .σσ ϕϑ
mm 5≈Zσ
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2727
Energy ReconstructionEnergy Reconstruction
FWH
M(E
)/E (%
)FW
HM
(E)/E
(%)
FWHM FWHM ≈≈ 4.1 % 4.1 %
Asymptotic value Asymptotic value FWHM FWHM ≈≈ 2.5 %2.5 % for for λλabsabs →∞→∞λλabsabs = 100 cm= 100 cm
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2828
Liquid Xenon Calorimeter PrototypeLiquid Xenon Calorimeter Prototype
0
1
Liquid Xenon
2 inch PMT
PMT holder
(x 228)
trigger counters
trigger counters
3
3
2
2
1
1
40 x 40 x 50 cm40 x 40 x 50 cm33;;228 228 PMTsPMTs, , 100 l100 litresitres Liquid XenonLiquid Xenon(the (the largestlargest in the World).in the World).PurposesPurposes: :
Test Test cryogenic operationscryogenic operations on a on a long termlong term and on a and on a large volumelarge volume;;Measure the Measure the Liquid Xenon propertiesLiquid Xenon properties;;Check the Check the reconstruction methodsreconstruction methods;;Measure the Measure the Energy, Position and Energy, Position and Timing resolutionsTiming resolutions with:with:a) a) Cosmic raysCosmic rays;;b) b) αα--sourcessources;;c) c) 6060 MeVMeV e¯e¯ from from KSR storage ringKSR storage ring;;d) d) 4040 MeVMeV γγ from from TERASTERAS
Compton BackscatteringCompton Backscattering;;e) e) ee++ andand 5050 MeVMeV γγ from from ππ°° atat PSIPSI. .
The Large Prototype (LP)
Planned this yearPlanned this year
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 2929
The LP from “inside”The LP from “inside”
LEDsα-source
αα--sources sources andand
LEDsLEDs for for PMTPMT
calibrationcalibration and and
monitoringmonitoring
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3030
Measurement of Measurement of LXeLXe Optical PropertiesOptical Properties
First testsFirst tests showed a number ofshowed a number of scintillation photonsscintillation photons much lowermuch lower than expected.than expected.
ItIt improvedimproved withwith Xenon purificationXenon purification:: OxysorbOxysorb + gas getter + re+ gas getter + re--circulationcirculation (took time).(took time).
There was a There was a strong absorptionstrong absorption due todue to contaminantscontaminants ((mainly Hmainly H22O, ~ 3O, ~ 3 ppmppm).).
March 2002March 2002 NowNow
)bxaexp(R +=
λλabsabs> 1 m> 1 m @ 90% C.L.@ 90% C.L.
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3131
Improvement of Improvement of λλabsabs with timewith timeWe observed We observed an improvementan improvement both both in comparisonin comparison withwith MC simulationMC simulation andand GXeGXe datadata
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3232
Radioactive Background in LPRadioactive Background in LPαα--triggertrigger with with 55××101066 gaingain;;
Geometrical cutsGeometrical cuts to to exclude exclude αα--sources;sources;
Energy scaleEnergy scale: : αα--sourcesource208208Tl (2.59±0.06) MeVTl (2.59±0.06) MeV4040K (1.42 ± 0.06) MeVK (1.42 ± 0.06) MeV
Other lines ?? Other lines ??
uniformuniform on the on the front facefront face;;
few 10 minfew 10 min (with (with nonnon--dedicated triggerdedicated trigger););
nice calibrationnice calibration forfor low low energy energy γγ’’ss..
4040KK (1.461 MeV)(1.461 MeV)
208208TlTl (2.614 MeV)(2.614 MeV)
Never seen before !Never seen before !
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3333
Timing Resolution MeasurementsTiming Resolution Measurements∆∆tt = (= (∆∆ttzz
22 + + ∆∆ttscsc22))1/21/2 = (80= (8022 + 60+ 6022))1/21/2 psps = 100 = 100 ps ps (FWHM)(FWHM)
∆∆ttzz TimeTime--jitter jitter due todue to γγ interaction pointinteraction point (MC:(MC: ))∆∆ttscsc Scintillation timeScintillation time andand photon statisticsphoton statistics
Measurement of Measurement of ∆∆ttscsc22 withwith 60 MeV 60 MeV electron beamelectron beam @ @ Kyoto Sincrotron RingKyoto Sincrotron Ring
(N.B. (N.B. Electron energy spectrum degradedElectron energy spectrum degradedby materials in front of the detector)by materials in front of the detector)
our goalour goal
• weighted averageweighted average of the of the PMT PMT TDCsTDCstimetime--walk corrected;walk corrected;
•• ∆∆ttscsc vsvs number of number of photoelectronsphotoelectrons;;
•• extrapolationextrapolation @ @ 52.852.8 MeMeVV is is okok;;
•• newnew PMTPMT with improved with improved QEQE:: 5 5 ⇒⇒10 %10 %
52.852.8 MeVMeV
5 %5 %10 %10 %
ps ∆tmm z 705 ≈→≈zσ
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3434
PMT characterization: PMT characterization: Cryogenic Test Facility in PisaCryogenic Test Facility in Pisa
Full designFull design and and mechanical mechanical drawingsdrawings completedcompleted;;Cryostat Cryostat delivereddelivered at the beginning of april;at the beginning of april;Orders madeOrders made for for dry UHV dry UHV pumping group, leak detector, pumping group, leak detector, UHV components, cryogenic UHV components, cryogenic bottle, PMT’sbottle, PMT’s …; …; somesome of them of them already already receivedreceived;;LaboratoryLaboratory in preparationin preparation..
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3535
TriggerTrigger
1 board
2 VME 6U
1 VME 9U
Type2
Type2
LXeLXe inner inner faceface
(312 PMT)(312 PMT)
. . .
20 boards
20 x 48
Type1Type1Type1
16
3
Type2
2 boards
. . .
10 boards
10 x 48
Type1Type1Type1
16
3
LXeLXe lateral lateral facesfaces
(488 PMT: (488 PMT: 4:1 fan4:1 fan--in)in) Type2
1 board
. . . 12 boards
12 x 48
Type1Type1Type1
16
3
Timing Timing counterscounters
(160 PMT)(160 PMT) Type2Type2
2 boards2 x 48
4 x 48
2 x 48
• Based on Based on simple quantitiessimple quantities::•• γγ energy (QSUM)energy (QSUM);;•• ee++ -- γγ coincidencecoincidencein in timetime and and directiondirection;;
•• LXeLXe & & Timing CounterTiming Counterinformationinformation (no DC).(no DC).
•• Built on a Built on a FADCFADC--FPGA FPGA architecturearchitecture;;
•• More complex algorithmsMore complex algorithmsimplementableimplementable..
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3636
Trigger PerformancesTrigger Performances
Beam rateBeam rate 10108 8 ss--11
Fast LXeFast LXe energy sum > 45 MeVenergy sum > 45 MeV 22××10103 3 ss--11
γγ interaction pointinteraction point (PMT of max charge)(PMT of max charge)ee++ hit pointhit point in timing counterin timing counter
time correlationtime correlation γγ –– ee++ 2200 s00 s--11
angular correlationangular correlation γγ –– ee++ 220 s0 s--11
Design Design andand simulation simulation of of type1 boardtype1 board completedcompleted;;
Prototype boardPrototype board delivereddelivered by late spring.by late spring.
Trigger StatusTrigger Status
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3737
Readout ElectronicsReadout Electronics
Waveform digitising for all channelsWaveform digitising for all channels;;Custom Custom domino sampling chipdomino sampling chip designed @ designed @ PSIPSI;;Cost per DSC Cost per DSC ~ 1 US$~ 1 US$;;2.5 GHz2.5 GHz sampling speed @ sampling speed @ 40 40 psps timing timing resolutionresolution;;Sampling depth Sampling depth 1024 bins1024 bins;;Readout similar to triggerReadout similar to trigger..
Prototypes delivered in autumn
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3838
SensitivitySensitivity
BR BR ((µµ e e γγ)) ≈≈ 1 1 •• 1010--1313Upper Limit @ 90 % C.L.Upper Limit @ 90 % C.L.BRBRaccacc ∝∝ RRµµ •• ∆∆EEee •• ((∆∆EEγγ))22 •• ((∆θ∆θεγεγ))22 •• ∆∆ttεγεγ ≈≈ 3 3 •• 1010--1414Accidental BackgroundAccidental Background
BRBRcorrcorr ≈≈ 3 3 •• 1010--1515Correlated BackgroundCorrelated Background
NNsigsig = BR = BR •• T T •• RRµµ •• ΩΩ/4/4ππ •• εεe e εεselsel εεγγSignalSignalSES = 1/(T SES = 1/(T •• RRµµ •• ΩΩ/4/4ππ •• εεe e εεselsel εεγ γ )) ≈≈ 4 4 •• 1010--1414Single Event SensitivitySingle Event Sensitivity
εεγγ ≈ 0.60.6
4 events4 events ((P = 2 P = 2 •• 1010--33) correspond to ) correspond to BR =BR = 2 2 •• 1010--1313DiscoveryDiscovery
εεselsel ≈ (0.9)(0.9)33 = 0.7= 0.7εεee ≈ 0.90.9
ΩΩ/4/4ππ = 0.09= 0.09Detector parametersDetector parametersRRµµ = 0.3 = 0.3 •• 101088 µµ++/s/s
T = 2.6 T = 2.6 •• 10107 7 ss
Cuts @ Cuts @ 1.4 FWHM1.4 FWHM
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 3939
Conclusions and Time ScheduleConclusions and Time ScheduleThe experiment may The experiment may provide a clean indicationprovide a clean indication of of New Physics (SUSY)New Physics (SUSY); ;
MeasurementsMeasurements and and detector simulationdetector simulation make us confident that make us confident that we can reach a SES of we can reach a SES of 4 4 •• 1010--1414 for for µµ→→eeγγ (( BR BR ≈ 1010--1313););
Final prototypesFinal prototypes will be ready and measured within will be ready and measured within November 2003November 2003::
•• Large PrototypeLarge Prototype for for photon energyphoton energy, , positionposition and and timing resolutionstiming resolutions;;
•• Full scale Drift ChamberFull scale Drift Chamber;;
•• µµ--TransportTransport and and degraderdegrader--targettarget..
Experiment approvedExperiment approved by by INFNINFN--CSN1CSN1 at beginning of April.at beginning of April.
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Planning R & D Assembly Data Taking
NowNowLoILoI ProposalProposalRevisedRevised
documentdocument
Tentative time scheduleTentative time schedule http://meg.psi.chhttp://meg.pi.infn.it
http://meg.icepp.s.u-tokyo.ac.jp
http://meg.psi.chhttp://meg.psi.chhttp://meg.pi.infn.ithttp://meg.pi.infn.it
http://meg.icepp.s.uhttp://meg.icepp.s.u--tokyo.ac.jptokyo.ac.jp
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 4040
LxeLxe Calorimeter CalibrationCalorimeter Calibration
opening angle (deg)
Ene
rgy
(MeV
)
50
55
60
65
70
75
80
85
150 155 160 165 170 175 180
Energy (MeV)
Ent
ries
/0.1
MeV
0
1000
2000
3000
4000
5000
6000
7000
8000
50 55 60 65 70 75 80 85 90
π-
γ
γ
Requiring Requiring θ θ > > 170170οο
FWHM = 1.3FWHM = 1.3 MeVMeVRequiring Requiring θθ > 175> 175oo
FWHM = 0.3FWHM = 0.3 MeVMeV
ππ00EEγγ
Eγ
θθ
θ
170o
175o
Eγ
54.9 MeV 82.9 MeV1.3 1.3 MeVMeV for for θθ>170>170oo
0.30.3 MeVMeV for for θθ>175>175oo
1.1. ππ--p p ππ00nn
ππ0 0 ((2828 MeVMeV/c/c) ) γ γγ γ
54.954.9 MeVMeV < < E(E(γγ)) < < 82.982.9 MeVMeV
1.1. AmAm--BeBe γ γ sourcesource 4.434.43 MeVMeV
2.2. ππ--p p γ γ nn
E(E(γγ)) = = 129.4129.4 MeVMeV
Eγ
Lecce, April 24, 2003Lecce, April 24, 2003 Fabrizio CeiFabrizio Cei 4141
LXeLXe Calorimeter Calibration (2)Calorimeter Calibration (2)µ µ eeγννγνν
EEee > 0.85; > 0.85; EEγγ > 0.8; > 0.8; θθeeγγ > 120> 120oo
•Crystal boxCrystal boxPRDPRD 3838 (1988) (1988) 20772077
R.R.TribbleTribble’’ss talk attalk atUniv. of Tokyo Oct. 1999Univ. of Tokyo Oct. 1999
te-tγ
150 150 psps1
5 ~ 65 ~ 6
te-tγ
150 150 psps
1
0.3 ~ 0.40.3 ~ 0.4
108 µ/s10108 8 µµ/s/s
107 µ/sSignal 1/10
Background <1/100
10107 7 µµ/s/sSignal 1/10Signal 1/10
Background <1/100Background <1/100
Accidental backgroundAccidental background
Accidental backgroundAccidental background