New Results from the MEG Experiment Jeanine Adam on behalf of the MEG Collaboration Zurich PhD Seminar 2011 29th August 2011 / ETH Zurich

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch Contents MEG Experiment Introduction Detector Calibrations Data Taking Run Overview Detector Performance Analysis 2009 2010 Alternatives 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Introduction: Goal and Signature MEG Experiment Data Taking Analysis Introduction Detector Calibrations Introduction: Goal and Signature Goal: Search for the lepton flavor violating decay with a sensitivity of 10 -13 in branching ratio (current upper limit by MEGA: 1.2 · 10 -11) An observation of this decay will reveal new physics beyond the SM! Signature of signal event ( decay at rest): and emitted back-to-back Each and carries an energy of 52.8 MeV Coincident in time Background Radiative muon decay:  → e    Precise measurements of kinematic variables for photon and positron are crucial! Accidental coincidence:  → e   +  08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Introduction: MEG Experiment Data Taking Analysis Introduction Detector Calibrations Introduction: MEG Experiment International collaboration (~80 physicists) MEG is located at the Paul Scherrer Institute (PSI) 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Detector: Beam and Target MEG Experiment Data Taking Analysis Introduction Detector Calibrations Detector: Beam and Target Beam Low momentum muons (28 MeV/c) Wien filter ( / separation) Superconducting beam transport solenoid (BTS) with degrader Stopping rate of 3 × 10 7 muons/sec Target 205 m polyethylene foil Slanted angle of 20.0° Holes (r = 5 mm) to check vertex reconstruction 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Introduction Detector Calibrations Detector: Overview Photon: Liquid xenon scintillation detector (position, timing, energy) Positron: COBRA positron spectrometer (position, timing, energy) 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Detector: Spectrometer MEG Experiment Data Taking Analysis Introduction Detector Calibrations Detector: Spectrometer COBRA Magnet Superconducting main magnet Gradient magnetic field (B = 0.49 – 1.27 Tesla) Timing Counters 2 x 15 plastic scintillator bars read out by PMTs 2 x 256 scintillation fibers read out by APDs Drift Chamber System 16 dc modules aligned radially to beam axis Low-mass construction (12.5 m thick Kapton foils with 250 nm Al deposition, He:C2H6 gas mixture) 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Detector: LXe Calorimeter MEG Experiment Data Taking Analysis Introduction Detector Calibrations Detector: LXe Calorimeter World’s largest liquid xenon detector Filled with 900 liter of LXe (T = 161-165 K) Scintillation light is picked up by 846 PMTs High purity at sub-ppm level to avoid scintillation light absorption due to impurities (water, oxygen) Calibration of LXe detector 2 x week (total 6 hours): LED → PMT gain calibration Alpha → PMT quantum efficiency calibration Cockcroft-Walton → Uniformity, stability Neutron Generator → Stability (beam off and on) Special calibration runs: CEX ( , ) → Energy scale, uniformity Cosmics → Alignment ... 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Calibrations: PMT Calibrations MEG Experiment Data Taking Analysis Introduction Detector Calibrations Calibrations: PMT Calibrations PMT Gain Calibrations: Several LEDs inside the LXe detector Can be flushed with different intensities Fit correlation between variance and mean of charge distributions to calculate gain of each PMT PMT QE Calibrations: 25 241Am sources (known positions) inside the detector Compare MC simulation with data to calculate QE of each PMT 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Introduction Detector Calibrations Calibrations: Cockcroft-Walton Proton Accelerator 1 MeV Cockcroft-Walton proton accelerator and a Li2B4O7 crystal target are used to excite the reactions Li(p,)Be and B(p,)C Reactions produce gamma lines of 4.4 / 11.7 / 17.6 MeV Check stability of the detector and correct non-uniformity of energy response 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Introduction Detector Calibrations Calibrations: Neutron Generator Since 2010 a pulsed neutron generator is used to obtain neutrons with good S/N ratio The thermalized neutrons are captured in Nickel producing a 9 MeV photon emission Data taking is possible during beam off / on periods: Similar spectra Very stable performance during 2010 NG data is used in 2011 as standard monitor tool 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch Data Taking 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Run Overview Performance Run Overview Run 2008 First MEG physics data taking period (3 months) Result published in Nuclear Physics B 834 (2010) 1 Improvements for 2009 / 2010 Stable drift chamber HV and Xenon light yield situation New drift chamber alignment (Millipede) Better understanding of positron correlations New / improved LXe calibration methods 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Run Overview Performance Run Overview Run 2009 Physics data taking DAQ time total: 35 days Muons on target: 0.65 · 10 14 Run 2010 Optimized beam (adjusted degrader) Improved time resolution situation Physics data taking DAQ time total: 56 days Muons on target: 1.10 · 10 14 Twice the statistics of 2009 data 2009 PSI accelerator maintenance work 2010 CEX run PSI accelerator maintenance work 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis Run Overview Performance Detector Performance 2009 2010 Gamma Energy (%) 1.9 Gamma Timing (ps) 96 67 Gamma Position (mm) 5 (u,v) / 6 (w) Gamma Efficiency (%) 58 59 e Timing (ps) 107 e Momentum (keV) 310 330 e Theta (mrad) 9.4 11.0 e Phi (mrad) 6.7 7.2 e Vertex (mm) 1.5 (z) / 1.1 (y) 2.0 (z) / 1.1 (y) e Efficiency* (%) 40 34 e-gamma timing (ps) 146 122 Trigger Efficiency (%) 91 92 * e efficiency = DC-TC matching efficiency x DC detection efficiency 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch Analysis 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis Blind box analysis, i.e. optimization of analysis and background studies are done in sidebands Likelihood fit: Parameters: Number of signal, radiative muon decay and accidental background events Observable: Determination of upper limit by Feldman & Cousins 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis 2009 Data Nsig = 3.4 (+6.6 / -4.4) UL = 9.6 · 10 -12 (90% CL) LL = 1.7 · 10 -13 (90% CL) Total Accidental Radiative Signal 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis 2010 Data Nsig = -2.2 (+5.0 / -1.9) UL = 1.7 · 10 -12 (90% CL) LL = --- Total Accidental Radiative Signal 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis Summary Nsig (best fit) BR LL (90% CL) BR UL (90% CL) 2009 3.4 1.7 · 10 -13 9.6 · 10 -12 2010 -2.2 --- 1.7 · 10 -12 2009 + 2010 -0.5 2.4 · 10 -12 MEG Result 2009+2010 data is consistent with “no signal” hypothesis Fitting was done by 3 analysis groups with different parameterizations, statistical approaches, ... with consistent results 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Analysis Alternatives MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis Alternatives Reduce 5 dim observable to a one dimensional discriminant variable: 2 different kind of analysis: Cut analysis (minimize sensitivity) Likelihood fit (same procedure as for the 5 dim observable) Advantages: Fast analysis Fast toyMC production Lsig, LBG, LRMD are the signal, accidental background and RMD likelihoods Likelihood Fit 2009 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Analysis Alternatives MEG Experiment Data Taking Analysis 2009 2010 Alternatives Analysis Alternatives Results of the Rsig cut analysis and the Rsig likelihood fit: Both the Rsig cut analysis and the likelihood fit results are consistent with the results of the three analysis groups The Rsig cut analysis result is very close to the official MEG result Use it for checks and estimations which couldn’t be done until now (too time consuming) UL (90% CL) Official Analysis Rsig Cut Analysis Rsig Likelihood Fit 2009 UL 9.6 · 10 -12 1.1 · 10 -11 2010 UL 1.7 · 10 -12 2.8 · 10 -12 1.8 · 10 -12 2009+2010 UL 2.4 · 10 -12 3.2 · 10 -12 2.6 · 10 -12 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch

Summary and Conclusion MEG Experiment Data Taking Analysis Summary and Conclusion The MEG experiment is searching for the LFV decay aiming a sensitivity of ~10 -13 Physics data taking started in 2008 2009+2010 data are consistent with “no signal” hypothesis New physics is now constrained by a 5x tighter upper limit: MEG is taking more physics data this and next year to reach ~10 -13 sensitivity 08/29/2011 Zurich PhD Seminar 2011 / Jeanine Adam / jeanine.adam@psi.ch