Status and perspectives of the MEG Experiment Fabrizio Cei INFN & University of Pisa On behalf of the MEG Collaboration 24th Rencontres de Blois Blois (France), May30th 2012 Blois, 30 May 2012 Fabrizio Cei 1 Outline Lepton Flavour Violation The MEG Experiment Results from 2009/2010 Data Analysis Present Status and Perspectives Conclusions Blois, 30 May 2012 Fabrizio Cei 2 Lepton Flavour Violation 1) Lepton Flavour Violation (LFV) not allowed in the minimal SM and predicted in the extended SM (including neutrino mixing) at a negligible level, not experimentally detectable (BR 10-55). On the contrary, LFV predicted in many SM extensions (i.e. SUSY models) at SUSY -(12÷14) 2 measurable levels (BR(meg) 10 ) mme g m e in case of discovery, unambiguous m 0 e evidence for Physics Beyond SM. Blois, 30 May 2012 Fabrizio Cei 3 Lepton Flavour Violation 2) Several LFV processes, sensitive to New Physics (NP) through “new” lepton-lepton coupling Anomalous m e m,t anomalous decays magnetic conversion moment Blois, 30 May 2012 Fabrizio Cei 4 The MEG Experiment Blois, 30 May 2012 Fabrizio Cei 5 Goal and signal Search for m eg LFV decay. Target sensitivity BR 10-13 wrt normal muon decay. Previous Upper Bound: BR 1.2 x 10-11 (MEGA, 2001) Signature: + + e m g - back-to-back topology; - energy equally shared + qeg = 180° between e and g; Ee = Eg = 52.8 MeV - simultaneous emission. Te = Tg Blois, 30 May 2012 Fabrizio Cei 6 Background 2 2 2 accidental Racc (Rm) * (Q) * (Eg) physical * T * Ee m e n n m e g n n m e g n n (radiative decay) O Muon rate to be used is ee g g a trade off between expected number of n eZ eZ g signal events and e+ m+ g background level; n n O Used 3 x 107 m+/s; + + n e m O Sensitivity is limited by accidental background; RRD = Rm* BR(m → enng) O High resolution 0.1 Racc g detectors and a continuous muon beam Blois, 30 May 2012 Fabrizio Cei are mandatory. 7 Part of Total 60 physicists Blois, 30 May 2012 Fabrizio Cei 8 The Detector World’s most intense continuous muon beam pE5 line @PSI (up to 108 stopped m+/s); Photon detection by a Liquid Xenon calorimeter; Positron detection by a Drift Chamber spectrometer for momentum and by scintillation bars for timing measurements. Blois, 30 May 2012 Fabrizio Cei 9 Overview of calibration system Needed to ensure: Required precision; Long term detector stability; Continuous checks for a detector based on innovative technology (LXe). Blois, 30 May 2012 Fabrizio Cei 10 Summary of MEG performances Blois, 30 May 2012 Fabrizio Cei 11 Results from 2009-2010 Data Blois, 30 May 2012 Fabrizio Cei 12 Blind + likelihood analysis Signal and bkg optimization done in sidebands Timing sidebands Eg sideband Events in the blind box ( 0.2%) are hidden RMD events up to the end of optimization procedure Blois, 30 May 2012 Fabrizio Cei 13 MEG likelihood analysis The most dangerous bck is measured ! Likelihood function Blois, 30 May 2012 Fabrizio Cei 14 PDF’s Blois, 30 May 2012 Fabrizio Cei 15 Normalization Neg BR(m e g )k where: fS (TRG 0|e g ) k Nenn A(g|track) (g ) Psc(22) fM (TRG 22|track em TC ) f A(DC ) (track, p 50MeV|DC ) (TC|p 50MeV) S e e S 7 10 pre-scaling f M M factor TRG = 22: Michel events trigger (only DCH track required) TRG = 0: MEG events trigger Blois, 30 May 2012 Fabrizio Cei 16 Data sets for 2009 & 2010 Muons on target 2009 Muons on target 2010 Statistics for 2010 about twice that for 2009 Stable detector conditions Optimized degrader (LXe, DC, TC) Improved electronics timing Slightly lower DC efficiency because of higher noise. Blois, 30 May 2012 Fabrizio Cei 17 Preliminary results @ICHEP 2010 (Data 2009) L R Log sig N.B. Plots shown only for sig 10 0.1L 0.9L Ranking variable RMD BG reference; not used in analysis Blois, 30 May 2012 Fabrizio Cei 18 Updates after ICHEP 2010 Used also 2010 data (statistics twice that of 2009); Improved detector alignment (cosmic rays, MILLEPEDE algorithm); Implementation of correlations between positron variables (energy, angles ...); Improved knowledge of magnetic field map; Improved likelihood analysis procedure; Combination of 2009 and 2010 data published paper PRL 107,171801,(2011) with new upper bound on m eg BR Blois, 30 May 2012 Fabrizio Cei 19 Sensitivity evaluation Upper limit averaged over a sample of 1000 toy MCs, generated with 0 signal events and using the background rate measured in the sidebands. Confirmed by applying the analysis procedure to events falling in timing and angular sidebands. Blois, 30 May 2012 Fabrizio Cei 20 Unbinned maximum likelihood fit 2009 Three independent analyses performed by different groups gave consistent results. Blois, 30 May 2012 Fabrizio Cei 21 Unbinned maximum likelihood fit 2010 Blois, 30 May 2012 Fabrizio Cei 22 Combination of 2009 and 2010 In 2009 a fluctuation of 3 events above the background was observed, consistent with zero signal events at 8% probability. Such a fluctuation disappeared in 2010. 2009-2010 compatibility at 15%. Because of higher statistics of 2010 sample, the combined limit is dominated by 2010 results. Then, no lower bound at 90% C.L. Blois, 30 May 2012 Fabrizio Cei 23 Combined result and BR Upper Bound 2009 && 2010 Factor five improvement wrt previous limit ! Sensitivity 1.6 x 10-12; difference due to 2009 fluctuation. Blois, 30 May 2012 Fabrizio Cei 24 MEG Constraints on New Physics MSSM with large tan b SUSY-Seesaw-Seesaw Recent results from n-oscillation exps (Daya Bay, Reno, T2K, Minos, Double Chooz) favour “large” q13 ( (7 ÷ 10) degrees). G. Isidori et al., PRD 75 (2007) 115019 S.Antusch et al., JHEP 11 (2006) 090 Blois, 30 May 2012 Fabrizio Cei 25 Future perspectives Blois, 30 May 2012 Fabrizio Cei 26 Data 2011 Number of stopping muons in 2011. Data statistics more than doubled: 2011 > (2009 + 2010) Smooth running conditions (except for a cryo-plant damage in November); Improved LXe calibration (NaI replaced by BGO); Higher DAQ Efficiency and live time (> 95 %); Preliminary measurements of resolutions/efficiencies gave results comparable with that of previous years; Analysis under way. Blois, 30 May 2012 Fabrizio Cei 27 Projected sensitivity Stopped m+ per year Evaluated by toy MC and likelihood analysis Expected final sensitivity: 5 x 10-13 Sensitivity increases slowly with DAQ time because of background/detector performances to hope to gain a further order of magnitude, we need to upgrade our detector ! Blois, 30 May 2012 Fabrizio Cei 28 Studies for a MEG upgrade Several studies under way to improve detector performances: Calorimeter readout by fine grain MPPC instead of PMTs Unique volume gas chamber Active target Timing Counter improvements Final goal: reach a sensitivity 5 x 10-14 Blois, 30 May 2012 Fabrizio Cei 29 Other searches Study of RMD events and measurement of RMD branching ratio and Michel parameters (included measurement of muon beam polarization). Paper in preparation. Search for exotic muon decays (mediated by pseudo-scalar particles or with massless Majorons). Blois, 30 May 2012 Fabrizio Cei 30 Conclusions The MEG Experiment is running since 2008 in the search for meg decay. Analysis of data collected in 2009 & 2010 established an Upper Bound on meg branching ratio of 2.4 x 10-12 @ 90% CL., a factor 5 improvement with respect to the previous limit. The result is already significant. At the end of data taking, MEG will reach a sensitivity 5 x 10-13 A null result with this final sensitivity will be a strong constraint for SUSY/BSM parameter space. Studies are under way for possible upgrades of the experiment in order to improve sensitivity by better detector resolutions. Blois, 30 May 2012 Fabrizio Cei 31 Backup slides Blois, 30 May 2012 Fabrizio Cei 32 Lepton Flavour Violation 3) Strong impact of LFV searches in particle physics development: beginning of lepton physics (Pontecorvo & Hincks, 1947); universality of Fermi interaction standard model (1955); flavour physics (> 1960); possibility to explore high mass SUSY scale (> 1000 TeV) and give insights about large mass range, parity violation, number of generations ... (now) 11 Examples of recent predictions - (L. Calibbi et al., Phys. Rev. D74, 011701, 2006) (L. Calibbi et al., )/10 g hep-ph 0909.2501 e MEGA → MEG m BR( MEG Goal Super B Babar+Belle M (GeV) MEGA NEW MEG LIMIT 2011 !!! 1/2 Blois, 30 May 2012 Fabrizio Cei 33 70 years of physics history linked with improving technologies m Cosmic BR < 0.1 Stopped p m beams BR < 1.2 x 10-11 Blois, 30 May 2012 Fabrizio Cei 34 The Paul Scherrer Institute (PSI) The most powerful continuous machine in the world; Proton energy 590 MeV; Power 1.2 MW; Nominal operational current 2.2 mA (to be further increased). Blois, 30 May 2012 Fabrizio Cei 35 The Sub-Detectors The world’s largest Liquid Sixteen Xenon calorimeter: modules, each one formed - 900 l by two - 846 PMT’s staggered - Thin entrance window layers of - E(FWHM)/E 5% plane wires plus cathode - sT 70 ps foils for - sq 8 mrad longitudinal - s 330 keV at 52.8 information. E All resolutions @52.8 MeV - s 10 mrad MeV q 2 x 15 scintillator Thin wall bars for positron timing superconducting (and position) and magnet (COBRA) trigger purposes. generating a graded magnetic field to sweep - sT 70 ps out high PT positrons. Bmax 1.26 T Blois, 30 May 2012 Fabrizio Cei 36 CEX calibration Signal energy Photons detected at opposite region boundaries of energy spectrum.