MEG – эксперимент по поиску распада  e 

1. MEG – эксперимент по поиску распада e Б.И.Хазин Институт ядерной физики им.Г.И. Будкера Новосибирск

2. Outline • Physics motivation • Experimental technique • The MEG detector and performances • Analysis • Summary and prospects

3. Quarks Quark mixing (CKM) t c b s u t Mixing in the charged Lepton sector? d m e Energy Leptons Neutrino Oscillations n t n Three generations of fundamental spin ½ fermions m n e g,W,Z0, g - spin 1 bosons 12 3 Generation Higgs? And other questions… Standard Model after hundred years of efforts

4. probes slepton mixing matrix SUSY SM Charged Lepton Flavor Violation cLFV decays in the SM are radiatively induced by neutrino masses and mixings at a negligible level • All SM extensions enhance the • rate through mixing in the high • energy sector of the theory • (other particles in the loop...) • Clear evidence for physics beyond • the SM background-free • Restrict parameter space of SM • extensions

5.  The brunt directions “Universal” interaction: • LFV decays • muon to electron conversion • anomalous magnetic moment of  and 

6. LFV couplings LFV Hunting

7. 1.210-11 (2.24.4)10-8 MEGA@LAMPF 1999 (TieTi)<4.310-12 (AueAu)<710-13 Bfactories 2010  SINDRUM II 2006 e  (29681)10-11 110-12 BNL E821 2004 SINDRUM 1988 Current status

8. LFV search history Hinks, Pontecorvo 1948 m is not an excited e !!! Feinberg 1955 nandne are different !!! .... Super B-Factories … MEG . . . Mu2e, COMET

9. The MEG collaboration A. Baldini C. Bemporad G. Boca P. W. Cattaneo G. Cavoto F. Cei C. Cerri A. De Bari M. De Gerone S. Dussoni K. Fratini L. Galli F. Gatti M. Grassi D. Nicolò M. Panareo R. Pazzi† G. Piredda F. Renga M. Rossella F. Sergiampietri G. Signorelli F. Tenchini C. Voena D. Zanello X. Bai E. Baracchini T. Doke Y. 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 D. N. Grigoriev F. Ignatov B. I. Khazin A. Korenchenko N. Kravchuk A. Popov Yu. V. Yudin J. Adam M. Hildebrandt P.-R. Kettle O. Kiselev A. Papa S. Ritt B. Golden G. Lim W. Molzon INFN & U Pisa UCIrvine Tokyo U. PSI JINR Dubna INFN & U Roma Waseda U. BINP Novosibirsk INFN & U Genova KEK INFN & U Pavia INFN & U Lecce

10. Decay topology RMD (B1.5%) Main background n m e g m  e nn g g m n g m  e nn g m or e g m n 180º n e e Annihilation in flight e Eγ = Ee = 52.8 MeV θγe = 180º e and γ in time High intensity DC muon beam and highest possible energy, spatial and temporal resolutions are required

11. Machine • 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 • pm= 28 MeV/c (8% width)

12. The MEG Detector e+ detectionmagnetic spectrometer composed by solenoidal magnetanddrift chambersfor momentum plastic countersfor timing g detectionLiquid Xenon detector based on the scintillation light - fast:4 / 22 / 45 ns - high LY:~ 0.8 * NaI - short X0:2.77 cm

13. The Photon Calorimeter Energy, position, timing of g • Homogeneous 0.9 m3 volume of liquid Xe • 10 % solid angle • 65 < r < 112 cm • |cosθ| < 0.35 |ϕ| < 60o • Only scintillation light • Read by 846 PMT • 2’’ photo-multiplier tubes • Maximum coverage FF (6.2 cm cell) • Immersed in liquid Xe • Low temperature (165 K) • Quartz window (178 nm) • Thin entrance wall • Singularly applied HV • Waveform digitizing @1.6 GHz • Pileup rejection

14. Drift chamber for positrons 16 drift chambers 2.5x10-4 X0 each one sz=900 mm sr=230mm

15. The Timing Counters Upstream and downstreamsectors 15x2 scintillating bars (4x4x79.6 cm) with PMT’s st60 ps -Measure e+ time of impact -Used in trigger time concidence with g matching positron direction 256 x 2 scintillating fibers (0.6x0.6x156 cm) read with APD

16. COBRA (COnstant Bending Radius) magnet solenoid emitted e+ +beam DC R Low energy electrons quickly swept away Constant bending radius independent of emission angles

17. Calibration

19. Analysis principle The blinding variables are Eg and teg A blind-box Hidden until analysis is fixed Three independent analyses different pdf implementation Fit or input NRMD, NBG different statistical treatment (Freq. or Bayes) Use of sidebands eg region

20. Likelihood analysis The likelihood function is built in terms of signal, radiative decay and accidental background Vector of observables Number of expected events in signal region S(x) – product of the measured detector response functions R(x) – convolution of theoretical RMD spectrum with response functions B(x) – product of response functions obtained from BG spectra in side-bands Normalization on Michel events Normalization on RMD is in agreement with Michel within 7%

21. Probability density functions

22. BR =0 probability = 8% Sensitivity = 3.3 x 10-12 Analysis of 2009 data Nsig best value = 3.4

23. Analysis of 2010 data No signal events

24. Combined 2009-2010analysis 1.8x1014 muon decays MEG result Sensitivity = 1.6 x 10-12 Systematic errors included (2% effect on UL) Larger contributions from relative angle offset, correlation in positron kinematical variables, normalization

25.  on target 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 meg • 2011 data taking goes well • MEG will continue to run this and • next year to reach a sensitivity of • few times x 10-13 Phys.Rev.Lett. 107, 171801 (2011) http://xxx.lanl.gov/abs/1107.5547

26. Future of cLFV 10-1610-18 210-9 SuperB 2015 few 10-13 Mu2e 2018 MEG to 2013  COMET 2017 e  10-1510-16 Δa=(???  34)10-11 3.68 Gm2 FNAL 2015 Heidelberg 2015

27. Спасибо