MEG – эксперимент по поиску распада e
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MEG – эксперимент по поиску распада e
Б.И.Хазин
Институт ядерной физики им.Г.И. БудкераНовосибирск
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Outline
Physics motivation Experimental technique The MEG detector and
performances Analysis Summary and prospects
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Standard Model after hundred years of efforts
d
tb
1 2 3Generation
Quarks
Leptons
e
cu s
e
En
erg
yQuark mixing (CKM)
Neutrino Oscillations
Mixing in the chargedLepton sector?
Three generations of fundamental spin ½ fermions
g,W,Z0, spin bosons
(3) (2) (1)C L YSU SU U
Higgs? And other questions…
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Charged Lepton Flavor ViolationcLFV decays in the SM are radiatively induced by neutrino masses and mixings at a negligible levelcLFV decays in the SM are radiatively induced by neutrino masses and mixings at a negligible level
o All SM extensions enhance the rate through mixing in the high energy sector of the theory (other particles in the loop...)
o Clear evidence for physics beyond the SM background-free
o Restrict parameter space of SM extensions
e0
e
SUSYSUSY
2em
probes slepton mixing matrix
e e
W
SMSM
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The brunt directions
μνij i μνFY σjl l“Universal” interaction:
LFV decaysmuon to electron conversionanomalous magnetic moment of and
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LFV coupling
s
LFV coupling
s
LFV Hunting
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Current status
(2.24.4)10-8
1.210-11
MEGA@LAMPFMEGA@LAMPF19991999
MEGA@LAMPFMEGA@LAMPF19991999
BB factoriesfactories20102010
BNL E821BNL E82120042004
BNL E821BNL E82120042004
(29681)10-11110-12
SINDRUMSINDRUM19881988
SINDRUMSINDRUM19881988
(TieTi)<4.310-12
(AueAu)<710-13
SINDRUM IISINDRUM II20062006
SINDRUM IISINDRUM II20062006
e
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LFV search history
........Super B-FactoriesSuper B-Factories
… MEG
Mu2e, COMETMu2e, COMET. . .. . .
Hinks, Pontecorvo 1948is not an excited e !!!Feinberg 1955ande are different !!!
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The MEG collaborationThe MEG collaborationThe MEG collaborationThe MEG collaboration
Tokyo U.Tokyo U.Waseda U.Waseda U.KEKKEK
INFN & U PisaINFN & U PisaINFN & U RomaINFN & U Roma
INFN & U GenovaINFN & U GenovaINFN & U PaviaINFN & U Pavia
INFN & U LecceINFN & U Lecce
PSIPSI UCIrvineUCIrvine JINR DubnaJINR DubnaBINP NovosibirskBINP Novosibirsk
J. AdamM. Hildebrandt P.-R. Kettle O. KiselevA. Papa
S. Ritt
J. AdamM. Hildebrandt P.-R. Kettle O. KiselevA. Papa
S. Ritt
X. Bai E. Baracchini T. DokeY. Fujii T. Haruyama T. Iwamoto A. Maki S. Mihara T. Mori H. Natori H. Nishiguchi Y. Nishimura W. Ootani R. Sawada Y. Uchiyama
A. Yamamoto
X. Bai E. Baracchini T. DokeY. Fujii T. Haruyama T. Iwamoto A. Maki S. Mihara T. Mori H. Natori H. Nishiguchi Y. Nishimura W. Ootani R. Sawada Y. Uchiyama
A. Yamamoto
A. Baldini C. Bemporad G. Boca P. W. Cattaneo G. Cavoto F. Cei C. Cerri A. De Bari M. De Gerone S. DussoniK. Fratini L. Galli F. Gatti M. GrassiD. Nicolò M. PanareoR. Pazzi† G. Piredda F. Renga
M. Rossella
A. Baldini C. Bemporad G. Boca P. W. Cattaneo G. Cavoto F. Cei C. Cerri A. De Bari M. De Gerone S. DussoniK. Fratini L. Galli F. Gatti M. GrassiD. Nicolò M. PanareoR. Pazzi† G. Piredda F. Renga
M. Rossella
B. Golden G. LimW. Molzon
B. Golden G. LimW. Molzon
F. Sergiampietri G. Signorelli F. TenchiniC. Voena
D. Zanello
F. Sergiampietri G. Signorelli F. TenchiniC. Voena
D. Zanello
D. N. Grigoriev F. Ignatov B. I. Khazin A. Korenchenko N. Kravchuk A. Popov
Yu. V. Yudin
D. N. Grigoriev F. Ignatov B. I. Khazin A. Korenchenko N. Kravchuk A. Popov
Yu. V. Yudin
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and 0.1promt accR R R
e
e
180º
Decay topology
Eγ = Ee = 52.8 MeVθγe = 180ºe and γ in time
e
e
e
Annihilationin flight
Main background
e
e
or
RMD (1.5%)
2 2 2( ) ( ) ( )acc e e eR R E E t
High intensity DC muon beam and highest possible energy, spatial and temporal resolutions are required
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MachineMachine•The most intense (continuous) muon beam: Paul Sherrer Institute (CH)•1.6 MW proton accelerator•2 ma of protons – towards 3 mA (replace with new resonant cavities) extremely stable > 3x108 surface muons/sec @ 2 mA pMeV/c (8% width)
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The MEG Detector
e+ detection magnetic spectrometer composed by solenoidal magnet and drift chambers for momentum
plastic counters for timing detection Liquid Xenon detector based on the scintillation light
- fast: 4 / 22 / 45 ns- high LY: ~ 0.8 * NaI- short X0: 2.77 cm
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Energy, position, timing of
Homogeneous 0.9 m3 volume of liquid Xe
10 % solid angle65 < r < 112 cm|cosθ| < 0.35 |ϕ| < 60o
Only scintillation lightRead by 846 PMT
2’’ photo-multiplier tubes Maximum coverage FF (6.2 cm cell)Immersed in liquid XeLow temperature (165 K)Quartz window (178 nm)
Thin entrance wallSingularly applied HVWaveform digitizing @1.6 GHz
Pileup rejection
The Photon Calorimeter
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Drift chamber for positrons
z=900 mr=230 m
16 drift chambers2.5x10-4 X0 each one
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The Timing Counters
15x2 scintillating bars (4x4x79.6 cm) with PMT’st60 ps
-Measure e+ time of impact-Used in trigger time concidence with matching positron direction
Upstream and downstream sectors
256 x 2 scintillating fibers (0.6x0.6x156 cm) read with APD
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COBRA (COnstant Bending Radius) magnet
R
Constant bending radius independent of emission angles
Low energy electrons quickly swept away
solenoid
+ beam emitted e+
DC
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Calibration
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Analysis principleAnalysis principleThe blinding variables are
Eand te
A blind-boxHidden until analysis is fixed
Three independent analyses
different pdf implementationFit or input NRMD, NBGdifferent statistical treatment(Freq. or Bayes)
Use of sidebands
The blinding variables are Eand te
A blind-boxHidden until analysis is fixed
Three independent analyses
different pdf implementationFit or input NRMD, NBGdifferent statistical treatment(Freq. or Bayes)
Use of sidebands
eregion
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Likelihood analysisThe likelihood function is built in terms of signal, radiative decay and accidental background
( , , , , )i e e e ex E E t
exp sig RMD BGN N N N
Vector of observables
Number of expected events in signal region
S(x) – product of the measured detector response functionsR(x) – convolution of theoretical RMD spectrum with response functionsB(x) – product of response functions obtained from BG spectra in side-bands
Normalization on Michel events
12( ) 1 1(1.0 0.1) 10
( )
accsig sig Michel
trig rec sigMichel Michel
N N fBr eN
Br e k N Psc A
exp22
( )( )
22
1
( , , ) ( ) ( ) ( )!
BG BGRMD RMDobs
BGRMD
N NN NN N
sig RMD BG sig i RMD i BG iiobs
eN N N e e N S x N R x N B x
N
L
Normalization on RMD is in agreement with Michel within 7%
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Probability density functions
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Analysis of 2009 data
Nsig best value = 3.4
BR =0 probability = 8%
Sensitivity = 3.3 x 10-12
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No signal events
Analysis of 2010 data
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Combined 2009-2010analysis
Sensitivity = 1.6 x 10-12
MEG result
Systematic errors included (2% effect on UL)Larger contributions from relative angle offset, correlation in positron kinematical variables, normalization
1.8x1014 muon decays
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Current result and prospects• 8% probability statistical fluctuations happen! •The combined analysis of 2009 and 2010 data is consistent with a null result and gives an UL (90% CL) of 2.4 x 10-12 : a constraint 5 times better than the previous best one to the existence of e• 2011 data taking goes well• MEG will continue to run this and next year to reach a sensitivity of few times x 10-13
on target
Phys.Rev.Lett. 107, 171801 (2011)http://xxx.lanl.gov/abs/1107.5547
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Future of cLFV
e
Mu2e 2018Mu2e 2018Mu2e 2018Mu2e 2018
10-1610-18
210-9
SuperBSuperB20152015
SuperBSuperB20152015
Gm2 FNALGm2 FNAL20152015
Gm2 FNALGm2 FNAL20152015
Δa=(??? 34)10-
11
3.68HeidelbergHeidelberg20152015
HeidelbergHeidelberg20152015
10-1510-16
few 10-13
MEGMEGto 2013to 2013
MEGMEGto 2013to 2013
COMET COMET 20172017
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Спасибо