1 / 34

Recent results from the MEG Experiment m +  e + g

Recent results from the MEG Experiment m +  e + g. Stefan Ritt Paul Scherrer Institute, Switzerland. Feb. 1993, Physik-Hochhaus. Agenda. Motivation to search for m  e g Experimental Technique: Beam, Detectors, Electronics Results from 2008 and 2009 data. g. g. W -. m -. e -.

maj
Download Presentation

Recent results from the MEG Experiment m +  e + g

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Recent results from the MEG Experimentm+ e+g Stefan Ritt Paul Scherrer Institute, Switzerland

  2. Feb. 1993, Physik-Hochhaus PIC2010

  3. Agenda • Motivation to search for m  e g • Experimental Technique: • Beam, Detectors, Electronics • Results from 2008 and 2009 data PIC2010

  4. g g W- m- e- m- e- nm ne LFV in SUSY • New physics through virtual loops in low energy precision experiments • While LFV is forbidden in SM, it is possible in SUSY “Beauty of MEG” Current experimental limit: BR(m e g) < 1.2 x 10-11 PIC2010

  5. ft(M)=2.4 m>0 Ml=50GeV 1) Current SUSY predictions current limit2) MEG goal “Supersymmetric parameterspace accessible by LHC” • J. Hisano et al., Phys. Lett. B391 (1997) 341 • MEGA collaboration, hep-ex/9905013 W. Buchmueller, DESY, priv. comm. PIC2010

  6. m→ e g mA→ eA m→ eee Physics Motivation • LVF in the neutrino sector was observed by several experiments • LVF in charged lepton sector: • m → eg < 1.2 x 10-11(MEGA) • mTi → eTi < 7 x 10-13 (SINDRUM II) • m → eee < 1 x 10-12 (SINDRUM II) • LVF is forbidden in SM but newtheories (e.G. SUSY-GUT) predictLVF at observable rates of10-11 to 10-14 • MEG Experiment aims at 10-13 cosmic m 10-1 10-2 10-3 10-4 10-5 stopped p 10-6 10-7 m beams 10-6 stopped m 10-9 10-10 SUSY SU(5) BR(m e g) = 10-13 mTi  eTi = 4x10-16BR(m eee) = 6x10-16 10-11 10-12 10-13 MEG 10-14 10-15 Mu2e 10-16 1940 1950 1960 1970 1980 1990 2000 2010 2020 PIC2010

  7. Decay Topology m  e g Signal Prompt Background Accidental Background 52.8 MeV g < 52.8 MeV Dominant g g n n n e n m m m 180º m n e e e n 52.8 MeV < 52.8 MeV < 52.8 MeV • m→ e g signal very clean • Eg = 52.8 MeV • Ee = 52.8 MeV • qge = 180º • e and g in time PIC2010

  8. ~60 People (35 FTEs) from five countries Tokyo U. Waseda U. KEK INFN & UniPisa Roma Genova Pavia Lecce PSI UC Irvine JINR DubnaBINP Novosibirsk PIC2010

  9. Proton Accelerator 590 MeV / 2.2 mA (1.3 MW) Swiss Light Source Paul Scherrer Institute PIC2010

  10. 1m Experimental Method COBRA Magnet Gradient field s.c. 1.27 T magnet sweeps out “high pt” e+ quickly Drift Chamber Ultra-light material Precise measurement of e+ tracks Muon Beam Most intense DC muon beam up to 108m/s on target Timing Counter Resolution <100ps in 1.4T B-field Liquid Xenon Calorimeter World’s largest LXe calorimeter~900 l (2.7t) with 846 PMTs immersed in Xenon Lots of pioneering work PIC2010

  11. A few pictures Stopping Target LXe calorimeterassembly PIC2010

  12. Laser 20 cm 3 cm Calorimeter Calibrations m radiative decay LED Laser g e Lower beam intensity < 107to reduce pile-ups A few days ~ 1 week to get enough statistics m (rough) relative timing calib. < 2~3 nsec n n PMT Gain Higher V with light att. Can be repeated frequently p0 gg p- + p  p0 + n p0  gg (55MeV, 83MeV) p- + p  g + n (129MeV) 10 days to scan all volume precisely LH2 target alpha MEG Detector Standard Calibrations PMT QE & Att. L Cold GXe LXe e+ g e- Nickel g Generator Proton Acc Li(p,)Be LiF target at COBRA center 17.6MeV g ~daily calib. Can be used also for initial setup 9 MeV Nickelγ-line on off Illuminate Xe from the back Source (Cf) transferred by comp air  on/off K Bi NaI Tl Li(p, 1) at 14.6 MeV F Polyethylene 0.25 cm Nickel plate Li(p, 0) at 17.6 MeV PIC2010

  13. The DRS chip • DRS chip developed at PSI • 5 GHz sampling speed, 12 bits resolution • 3000 Channels installed in MEG for excellent pile-up recognition and timing resolution • Use in many other experiments mainly in Asto-particle physics (MAGIC, Veritas, CTA) 32 channels input Problem: Pile-up PIC2010

  14. Running periods • 2008 Result: • 78 days physics data taking • Expected U.L.: ~1.3x10-11 • 90% U.L.: 2.8x10-11 2008 Physics Run Sept.-Dec.Low efficiency and resolutions due to hardware problems • 2009 Run: • 43 days physics data taking • 22.3 M triggers • 93 TB data Hardware upgrades Data analysis 2009 Physics Run Nov.-Dec. Hardware upgrades Data analysis • 2010 Run: • Just starting • Estimated 117 days physicsdata taking 2010 Physics Run Aug.-Dec. Improved timing resolution Reduced noise in DC system PIC2010

  15. Performances HV problem  DC-TC matching PIC2010

  16. Blind Analysis Event Distribution without any selection: Blinding box (~10s) Kept blind during calibration and optimization e+ detector response from Michel decays radiative muon decays  timing resolution Eg sideband Measurement of accidental background “right” time sideband “left” time sideband PIC2010

  17. Maximum Likelihood Analysis Extended un-binned maximum likelihood analysis on number of events Probability Density Functions (PDF) fitting parameters for signal events (Nsig), prompt background (NRMD) and accidental background (NBG) PIC2010

  18. Eγ (MeV) 50 52 54 56 48 58 PDFs Eg Ee+ Tg-e+ Signal 55 MeV p0 calibration Measured resolution Measured RMD peak Relative Angle Measured resolutions and BG Background Sideband analysis Sideband analysis PIC2010

  19. 2009 Sensitivity from Sidebands Right time sideband Left time sideband Average 90% C.L. upper limit of toy MC assuming null signal: BR < 6.1 x 10-12 Sideband fit result: BR < 4~6 x 10-12 MEGA experiment: BR < 12 x 10-12 signal region For each plot, a cut on the other two variables is applied to contain roughly 90% of the signal region PIC2010

  20. Event distribution after un-blinding • Signal region un-blinded on July 6th 2010 • Events and analysis have not been touched afterwards • Different statistical approaches (Bayesian, Feldman-Cousins, …)have been applied by different groups PIC2010

  21. Likelihood Fit Result Preliminary! Total Acc. BG RMD Signal 90% U.L. Ee[GeV] Eg[GeV] Teg[s] • NRMD = 35  23 (expected from sideband: 32  2) • Best fit: Nsig = 3.0 • Nsig < 15 (90% C.L.) • BR < 15 x 10-12 (90% C.L.) • Nsig = 0 is still in 90% C.L. feg[rad] qeg[rad] Three groups applied different likelihood analysis with different statistical treatments to check possible systematic effects: Nsig = 3.0 – 4.5, BR < 12 – 15 x 10-12 NBG~1-2 NRMD~0.02 around signal region PIC2010

  22. Event Checks Vertex No strange behavior has been found so far PIC2010

  23. Event Quality Check All Events events around signal region stay High quality tracks = event category based on quality of number of DC hits, c2, and DC-TC matching, categorized before un-blinding PIC2010

  24. One of the most signal-like events Calorimeter sum waveform Run 59731 Event 1212 4. Dec. 2009, 21:50 Eg = 52.25 MeV Ee+ = 52.84 MeV Dqe+g = 178.8 degrees DTeg = 26.8 ps PIC2010

  25. What should a signal look like? Blue: Data Red: Signal from toy MC Clustering of events in Ee/Eg plane look different from what one would expect, no clustering in Teg/qeg plane. Data could still be consistent with background fluctuations. PIC2010

  26. Prospects 2010  refined analysis  monochromatic e+ beam  DC HV noise reduction  DRS4 optimization  TC fibers?  triple statistics! PIC2010

  27. Conclusions • Result 2008 • BR(meg) < 2.8 x 10-11, Nucl. Phys. B834, 1-12 (2010) • Preliminary result 2009 (only limited systematics) • Sensitivity: 0.61 x 10-11 • BR(meg) < 1.5 x 10-11 (90% C.L.) • Nsig=0 is in the 90% C.L. region, but probability to obtain Nsig=3.0 with null hypothesis is only 2-3 % • 2010 run has just started with improved resolutionsEstimated Sensitivity: 0.2 x 10-11followed by two more years of data taking. This should allow us to clarify the result. Acknowledgements:Ryu Sawada, Fabrizio Cei, Yusuke Uchiyama, Toshiyuki Iwamoto and the whole MEG crowd http://meg.psi.ch PIC2010

  28. Is there anything beyond the horizon? Is there anything beyond the horizon? PIC2010

  29. Backup Slides PIC2010

  30. Normalization • Normalization is done by Michel events (dedicated trigger, mixed events): MEG trigger Michel trigger prescaling factor = 107 By normalizing to Michel events, some factor cancel out in the first order k = 1.0  0.1 x 1012 Preliminary! PIC2010

  31. “Polarized” MEG • m are produced already polarized • Different target to keep m polarization • Angular distribution of decays predicteddifferently by different theories(compare Wu experiment for Parity Violation) Detector acceptance SU(5) SUSY-GUTA = +1 SO(10) SUSY-GUTA 0 MSSM with nRA = -1 Y.Kuno et al., Phys.Rev.Lett. 77 (1996) 434 PIC2010

  32. Expected Distribution • A = +1 • B (m+ e+ g) = 1 x 10-12 • 1 x 108m+/s • 5 x 107 s beam time (2 years) • Pm = 0.97 Signal +Background Background S. Yamada @ SUSY 2004, Tsukuba PIC2010

  33. Previous Experiments PIC2010

  34. g n m n e Radiative Muon Decay • This decay is a benchmark for the whole detector • Branching ratio 1.4% • Decays clearly visible in high rate environment m  e nn g T(g) – T(e+) PIC2010

More Related