Status of MEG-I physics analysis Fabrizio Cei INFN & University of Pisa Pisa, 15 September 2014 15/09/2014 Fabrizio Cei

Summary of MEG results in 2013 Improved reconstruction algorithms and reconstruction efficiency on both e+ and g sides; Analyzed 2009/2010 & 2011 samples; total number of 3.6 x 1014 muons stopped on target; Reached sensitivity of 7.7 x 10-13 Upper limit on m+ e+ g branching ratio: 5.7 x 10-13 (90% C.L.) factor 4 improvement ! Published in PRL 110 (2013) 201801 NSIG  BR (normalization factor) x 10-12 15/09/2014 Fabrizio Cei

Analysis strategy Likelihood + Blind (only 2011) analysis Signal and background optimization done in sidebands Timing sidebands Eg sideband Events in the blind box ( 0.2%) are hidden up to the end of optimization procedure (only 2011) RMD events 15/09/2014 Fabrizio Cei

Impact of MEG: t mg vs meg < 2013 Blankenburg et al. Eur.Phys.J. C72 (2012) 2126 Antusch et al. JHEP 0611 (2006) 090  MEG 2011 excluded MEG 2011 excluded q13 recently measured by Daya Bay, Reno, Double Chooz ... (7 ÷ 10o) MEG 2011 = PRL 107 (2011) 181201 15/09/2014 Fabrizio Cei

t mg vs meg NOW MEG 2013 = PRL 110 (2013) 201801 Blankenburg et al. Eur.Phys.J. C72 (2012) 2126 Antusch et al. JHEP 0611 (2006) 090  MEG 2013 excluded More than 150 citations on INSPIRE ! MEG 2013 excluded MEG 2013 = PRL 110 (2013) 201801 q13 recently measured by Daya Bay, Reno, Double Chooz ... (7 ÷ 10o) 15/09/2014 Fabrizio Cei

Full MEG sample Number of m+  e+g events = (k factor) x BR (m+  e +g) BR < 5.7 x 10-13 S = 7.7 x 10-13 (2012 + 2013)  (2009 + 2010 + 2011) Double statistics ! Estimated final sensitivity (toy MC)  (4 ÷ 5) x 10-13 BR < 2.4 x 10-12 S = 1.6 x 10-12 15/09/2014 Fabrizio Cei

2012 and 2013 analysis Data 2012/2013 processed with algorithms developed on 2011; 2012: - resolutions in substantial agreement with that of previous years; - preliminary normalization factor: 5.29 x 1012 (it was 4.0 x 1012 on 2011); - optimization almost finished; 2013: - some problems with DCH/target alignment (work in progress); - optimization under way. Unblinding in some months, if no reprocessing will be needed (see next slide) 15/09/2014 Fabrizio Cei

Open issues 1) Magnetic field measured in the area in Spring; Found a problem in measurement machine  measurements repeated in July and August; Analysis and computation of new map of magnetic field by splining algorithms under way; Next step: comparison of reconstructed positron variables (momentum and direction) with new and old magnetic field on a sample of data. If no significant differences will be found, no new reprocessing will be needed; otherwise … (this would delay the publication of final results). 15/09/2014 Fabrizio Cei

Open issues: 2) Analysis techniques to: - identify candidate events of positron Annihilation in Flight; - reconstruct events where a positron turn in DCH system was missed; were developed. Tested on 2009 data. Expected sensitivity improvement by  15%. Implementation for all years under way. 15/09/2014 Fabrizio Cei

Final MEG paper All MEG results will be published in a single long write-up paper; Chosen editorial board; already operating; Several persons will contribute; Writing of paper will start soon (some sections can be written without knowing the final results); Hopefully paper will be sent to a journal in few months. 15/09/2014 Fabrizio Cei

Beam polarization measurement A preliminary measurement of beam polarization was performed in 2010 by using Michel positrons ( 37000 events) from 2009 data: POL = 0.89 ± 0.03, in agreement with calculations; Analysis under way to improve the statistics by using 2010 and 2011 data ( 180000 evts ) and publish a result. Unfortunately, polarization traces are masked by detector instabilities and not perfect centering of beam wrt target and DCH system  dependence of spectrometer acceptance on positron zenith angle  MC corrections needed (under testing). However, data well reproduced by MC simulations with large polarization (including detector instabilities and beam/target displacements) and totally inconsistent with MC with POL = 0. (US-DS)/(US + DS) vs energy for all years together BLUE: DATA RED: MC with POL = 0.9 For POL = 0, MC predicts asymmetry consistent with zero, even including detector effects. 15/09/2014 Fabrizio Cei

Conclusions New limit on m+ e+ g branching ratio set by MEG (5.7 x 10-13) is a significant constrain for BSM theories. Sensitivity will be improved by a factor 1.5 when the full MEG sample (2009 – 2013) will be processed. New analysis technique for identifying AIF and missing turn events could further improve the sensitivity by  15%. Final results will be published in a long MEG summary paper. Analysis of recent measurements of magnetic field under way. We are trying to finalize the measurement of beam polarization. 15/09/2014 Fabrizio Cei