m e g search at PSI: SU GRA indications

1. SUSY SU(5) predictions BR (meg)  10-14  10-13 SUSY SO(10) predictions BRSO(10) 100 BRSU(5) Experimental limit Our goal megsearch at PSI: SUGRA indications LFV induced by slepton mixing R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 combinedLEP results favour tanb>10 in the Standard Model !!

2. qeg = 180° e+ +g Ee= Eg=52.8MeV Experimental method Easy signal selection with +at rest • Detector outline • Stopped beam of 3 107  /sec in a 150 mm target • Liquid Xenon calorimeter for  detection (scintillation) • fast:4 / 22 / 45 ns • high LY: ~ 0.8 * NaI • short X0:2.77 cm • Solenoid spectrometer & drift chambers fore+ momentum • Scintillation counters for e+ timing

3. The MEG collaboration INFN & Genova UniversityS. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle INFN & Lecce UniversityS. Spagnolo, C. Chiri, P. Creti, C. Gatto,G. Marsella, G. Palama’, M. Panareo, G. Tassielli INFN & Pavia UniversityA.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Pisa UniversityA. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, A. Papa, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN Roma I D. Zanello ICEPP, University of TokyoY. 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, TsukubaT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Waseda UniversityT. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamaguchi PSI, VilligenJ. Egger, P. Kettle, M. Hildebrandt, S. Ritt, M. Schneebeli Budker Institute, NovosibirskL.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

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

5. High pT positrons quickly swept out Uniform field Gradient field • Constant bending radius independent of emission angles Gradient field Uniform field COnstantBendingRAdius(COBRA) spectrometer Ready: at PSI !! • Bc = 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 X0)

6. Positron Tracker (PSI) • 17 chamber sectors aligned radially with 10°intervals • Two staggered arrays of drift cells • Chamber gas: He-C2H6 mixture • Vernier pattern to measure z-position made of 15 mm kapton foils goals (X,Y) ~200 mm (drift time) (Z) ~ 300 mm (charge division vernier strips) OK To be proved in mag.field

7. Positron Timing Counter (Pavia + Genova + Roma ) BC404 • 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 5 x 5 mm2

8. 800 l of Liquid Xe ~800 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume 40 MeV  and 1 mm collimator Liquid Xe calorimeter (Pisa + Tokyo + KEK) 55 MeV  • Measured position and energy resolutions with a 100 liters prototype • Cryostat in construction • 150 ps FWHM timing resolution proved R<1.5cm FWHM = 4.8 ± 0.3%

9. 2 boards LXe inner face (312 PMT) . . . . . . 10 boards 20 boards 1 board LXe lateral faces (488 PMT: 4 to 1 fan-in) 1 board 2 x 48 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 12 boards 2 boards 3 16 16 3 16 3 . . . Timing counters (160 PMT) Type2 Type2 Type2 Type2 Type2 Type2 2 VME 6U 1 VME 9U 2 x 48 4 x 48 20 x 48 12 x 48 10 x 48 Trigger Electronics (Pisa) • Uses easily quantities: •  energy • Positron-  coincidence in time and direction • Built on a FADC-FPGA architecture • More complex algorithms implementable • Beam rate 108 s-1 • Fast LXe energy sum > 45MeV 2103 s-1 g interaction point (PMT of max charge) e+ hit point in timing counter • time correlation g – e+ 200 s-1 • angular correlation g – e+ 20 s-1 Prototype board tested at PSI

10. Readout electronics (PSI): Domino Ring Sampler (DRS chip) Set of 1024 capacitors 40 MHz 11 bit 2.5 GHz • 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 • Prototype tested with 55 MeV photons in the 100 l prototype After calibrations raw • Spike structure will be simply fixed by re-programming FPGA on the board.

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

12. Sensitivity and time schedule • Total measurement time: 2 years (50% duty cycle of PSI beam) • One megevent 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 Revised document now LoI Proposal <LHC Planning R & D Assembly Data Taking 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp More details at