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 INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, A. Papa, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli ICEPP, University of Tokyo Y. Hisamatsu, T. Iwamoto, T. Mashimo, S. Mihara, T. Mori, H. Natori, H. Nishiguchi, W. Ootani, K. Ozone, R. Sawada, Y. Uchiyama, S. Yamada, S. Yamashita KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Waseda University T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamaguchi Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov PSI, Villigen J. Egger, P. Kettle, M. Hildebrandt, S. Ritt, M. Schneebeli INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Genova University S. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle INFN Roma I D. Zanello INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, C. Gatto,G. Marsella, G. Palama’, M. Panareo, G. Tassielli The MEG collaboration

4. MEG 4 Detector Construction Switzerland Drift Chambers Beam Line DAQ Japan LXe Calorimeter, Spectrometer’s magnet Russia LXe Tests Purification Italy e+ counter (Pv+Ge) Trigger (Pisa) LXe Calorimeter(Pisa) Splitters (Lecce)

5. MEG 5 COnstant Bending RAdius (COBRA) spectrometer 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 ) Ready: at PSI !!

6. MEG 6 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) ~ 300  m (charge division vernier strips) goals OK To be proved in mag.field

7. MEG 7 Positron Timing Counter (Pavia + Genova + Roma ) 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) Goal  time ~ 40 psec (100 ps FWHM) reached in tests BC404 5 x 5 mm 2

8. MEG 8 800 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 in construction 150 ps FWHM timing resolution proved

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 Prototype board tested at PSI

10. MEG 10 Readout electronics (PSI): Domino Ring Sampler (DRS chip) Analog Waveform digitizing for all channels Custom domino sampling chip designed at PSI 2.5 GHz sampling speed @ 40 ps timing resolution Sampling depth 1024 bins Readout similar to trigger Spike structure will be simply fixed by re-programming FPGA on the board. 2.5 GHz Set of 1024 capacitors 40 MHz 11 bit Prototype tested with 55 MeV photons in the 100 l prototype raw After calibrations

11. MEG 11 Sensitivity Summary Cuts at 1,4  FWHM Detector parameters Signal  4  10 -14 Single Event Sensitivity  2  10 -14  3  10 -15 Backgrounds Upper Limit at 90% CL BR (  e  )  1  10 -13

12. MEG 12 http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp Sensitivity and time schedule Total measurement time: 2 years (50% duty cycle of PSI beam) One  e  event observed if BR = 4 x 10 -14 If no event observed  upper BR limit at 90% CL = 10 -13 Discovery: 4 events (P = 2  10 -3 ) correspond to BR = 2  10 -13 Final prototypes being tested Full scale Drift Chamber Time profile More details at 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 PlanningR & D Assembly Data Taking now LoIProposal Reviseddocument <LHC