MEG – эксперимент по поиску распада e

Б.И.Хазин

Институт ядерной физики им.Г.И. БудкераНовосибирск

Outline

Physics motivation Experimental technique The MEG detector and

performances Analysis Summary and prospects

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…

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

The brunt directions

μνij i μνFY σjl l“Universal” interaction:

LFV decaysmuon to electron conversionanomalous magnetic moment of and

LFV coupling

s

LFV coupling

s

LFV Hunting

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

LFV search history

........Super B-FactoriesSuper B-Factories

… MEG

Mu2e, COMETMu2e, COMET. . .. . .

Hinks, Pontecorvo 1948is not an excited e !!!Feinberg 1955ande are different !!!

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

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

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)

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

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

Drift chamber for positrons

z=900 mr=230 m

16 drift chambers2.5x10-4 X0 each one

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

COBRA (COnstant Bending Radius) magnet

R

Constant bending radius independent of emission angles

Low energy electrons quickly swept away

solenoid

+ beam emitted e+

DC

Calibration

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

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%

Probability density functions

Analysis of 2009 data

Nsig best value = 3.4

BR =0 probability = 8%

Sensitivity = 3.3 x 10-12

No signal events

Analysis of 2010 data

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

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

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

Спасибо