1. MEG 1  e  search at PSI: SUGRA indications SUSY SU(5) predictions BR (  e  )  10 -14  10 -13 SUSY SO(10) predictions BR SO(10)  100 BR SU(5) R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al., Nucl. Phys. B445(1995) 215 LFV induced by slepton mixing Our goal Experimental limit combined LEP results favour tan  >10 in the Standard Model !!

2. MEG 2 Experimental method Easy signal selection with  + at rest e +  +  Ee = E  = 52.8 MeV  e  = 180° Detector outline Stopped beam of 3 10 7  /sec in a 150  m target Liquid Xenon calorimeter for  detection (scintillation) - fast: 4 / 22 / 45 ns - high LY: ~ 0.8 * NaI - short X 0 : 2.77 cm Solenoid spectrometer & drift chambers for e + momentum Scintillation counters for e + timing

3. MEG 3 Univ. of Tokyo Y. Hisamatsu, T. Iwamoto, T. Mashimo, S. Mihara, T. Mori, Y. Morita, H. Natori, H. Nishiguchi, Y. Nishimura, W. Ootani, K. Ozone, R. Sawada, Y. Uchiyama, S. Yamashita KEK T. Haruyama, K. Kasami, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Waseda Univ. K. Deguchi, T. Doke, J. Kikuchi, S. Suzuki, K. Terasawa INFN Pisa A. Baldini, C. Bemporad, F. Cei, C.Cerri, L.del Frate, L. Galli, G. Gallucci, M. Grassi, F. Morsani, D. Nicolò, A. Papa, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN and Univ. of Genova S. Cuneo, M. de Gerone, S. Dussoni, F. Gatti, S. Minutoli, P. Musico, P. Ottonello, R. Valle INFN and Univ. of Pavia G. Boca, P. W. Cattaneo, G. Cecchet, A. De Bari, M. Rossella INFN and Univ. of Roma I A. Barchiesi, G. Cavoto, G. Piredda, C. Voena, D. Zanello INFN and Univ. of Lecce P. Creti, G. Palama’, M. Panareo Paul Scherrer Institute J. Egger, P.-R. Kettle, M. Hildebrandt, S.Ritt BINP Novosibirsk L. M. Barkov, A. A. Grebenuk, D. N. Grigoriev, B. I. Khazin, N. M. Ryskulov JINR Dubna A. Korenchenko, N. Kravchuk, A. Moiseenko, D. Mzavia Univ. of California, Irvine W. Molzon, M. Hebert, P. Huwe, J. Perry, V. Tumakov, F. Xiao, S. Yamada MEG  ~40 FTEs The MEG collaboration

4. MEG 4 COnstant Bending RAdius (COBRA) spectrometer (KEK) Gradient field Uniform field Constant bending radius independent of emission angles High p T positrons quickly swept out Gradient field Uniform field B c = 1.26T current = 359A Five coils with three different diameters Compensation coils to suppress the stray field around the LXe detector High-strength aluminum stabilized superconductor  thin magnet (1.46 cm Aluminum, 0.2 X 0 ) No quench during 4 months of 2007 run

5. MEG 5 Positron Tracker (PSI) 17 chamber sectors aligned radially with 10°intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Vernier pattern to measure z-position made of 15  m kapton foils  (X,Y) ~200  m (drift time)  (Z) ~ 800  m (charge division vernier strips) goals proved in the experiment

6. MEG 6 Positron Timing Counter (Pavia + Genova + Roma 1 ) One (outer) layer of scintillator read by PMTs : timing One inner layer of scintillating fibers read by APDs: trigger (the long. Position is needed for a fast estimate of the positron direction)  time ~ 40 psec (100 ps FWHM) reached in tests BC404 5 x 5 mm 2

7. MEG 7 800 l of Liquid Xe ~800 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume Liquid Xe calorimeter (Pisa + Tokyo + KEK) FWHM = 4.8 ± 0.3% 55 MeV  R<1.5cm 40 MeV  and 1 mm collimator Measured position and energy resolutions with a 100 liters prototype Cryostat 150 ps FWHM timing resolution proved

8. MEG 8 17.6 MeV  /E R = 7.5 10 -2 measured with a NaI 14.6 MeV 6.13 MeV LiF target  Daily calibrations Daily calibrations by means of a 1 MeV Cockroft-Walton proton accelerator and changeable targets (Pisa)

9. MEG 9 Trigger Electronics (Pisa)  Beam rate10 8 s -1  Fast LXe energy sum > 45MeV2  10 3 s -1 g interaction point (PMT of max charge) e + hit point in timing counter  time correlation  – e + 200 s -1  angular correlation  – e + 20 s -1 Uses easily quantities:  energy Positron-  coincidence in time and direction Built on a FADC-FPGA architecture More complex algorithms implementable 1 board 2 VME 6U 1 VME 9U Type2 LXe inner face (312 PMT)... 20 boards 20 x 48 Type1 16 3 Type2 2 boards... 10 boards 10 x 48 Type1 16 3 LXe lateral faces (488 PMT: 4 to 1 fan-in) Type2 1 board... 12 boards 12 x 48 Type1 16 3 Timing counters (160 PMT) Type2 2 boards 2 x 48 4 x 48 2 x 48

10. MEG 10 Readout electronics (PSI): Domino Ring Sampler (DRS chip) Analog Waveform digitizing for all channels Custom domino sampling chip designed at PSI 2 GHz sampling speed Sampling depth 1024 bins Readout similar to trigger 2.5 GHz Set of 1024 capacitors 40 MHz 11 bit TC signals digitization

11. MEG 11 Data taking started in september 2007 Full apparatus CW beam line

12. MEG 12 http://meg.pi.infn.it : in italian http://meg.psi.ch : official home page http://meg.pi.infn.it : in italian http://meg.psi.ch : official home page Time Scale Goal: significant result before entering the LHC era Measurements and detector simulation show that it is possible to reach a sensitivity to BR =10 -13 for  e  and possibly below… in 3 years of data taking More details at 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Planning R & D Assembly Data Taking now LoI Proposal