A new m  e g experiment at PSI

A new m e g experiment at PSI For the MUEGAMMA collaboration Stefan Ritt (Paul Scherrer Institute, Switzerland) • Introduction • Experimental Technique • Current status NOON 2000

Physics Motivation • SUSY theories generically predict LFV • LFV forbidden by Standard Model • Processes like m+e+g are not “contaminated” by SM processes and therefore very clean • Discovered n oscillations are expected to enhance LFV rate • The search for m+e+g is therefore a promising field to find physics beyond the SM NOON 2000

Prediction from SUSY SU(5) ft(M)=2.4 m>0 Ml=50GeV 1) Current experimental bound 2) This experiment • J. Hisano et al., Phys. Lett. B391 (1997) 341 • MEGA collaboration, hep-ex/9905013 NOON 2000

Connection with n oscillations1) 2) This experiment • J. Hisano and D. Nomura, Phys. Rev. D59 (1999) 116005 • MEGA collaboration, hep-ex/9905013 NOON 2000

Previous m+e+g Experiments • New experiment: 10-14 at PSI • Letter of Intend 1998 • Proposal 1999, approved May 1999 NOON 2000

MEG Collaboration 35 7 NOON 2000

Kinematics qeg= 180° g e m Ee = 52.8 MeV Eg = 52.8 MeV Experimental Method • Stopped m beam of 108 s-1, 100% duty factor • Liquid Xe calorimeter for g detection • Solenoidal magnetic spectrometer with gradient field • Radial drift chambers for e+ momentum determination • Timing counter for e+ NOON 2000

meg g m e m e Signal and Background • m+ e+g signal very clear • Eg = Ee+ = 52.8 MeV • qge+ = 180° • e+ and g in time • Background • Radiative m+ decays • Accidental overlap • Detector Requirements • Excellent energy resolution • Excellent timing resolution • Good angular resolution menng men + g g n g m n e e m NOON 2000

Y = Eg/52.8MeV X = Ee/52.8MeV meg Signature •  eg Ee,Eg = 52.8MeV •  egnn Ee,Eg < 52.8MeV NOON 2000

Sensitivity and Background Rate BR(meg) = (Nm• T • W/4p• ee• eg• esel )-1 = 0.94  10-14 Prompt Background Bpr 10-17 Accidental Background Bacc DEe • Dteg • (DEg )2• (Dqeg )2  5  10-15 NOON 2000

Paul Scherrer Institute Experimental Hall NOON 2000

Experimental Hall NOON 2000

Sindrum II @ PSI Bue=4 •10-12 m-Ti  e-Ti : Oct. 2000 (50d) beam time: 90% C.L. limit: 6.1• 10-13 NOON 2000

pE5 Beam Line • 108m/s on 55 mm2 • Neutron background measured in 1998 • Beam test planned in Spring 2001 NOON 2000

Detector NOON 2000

H.V. Refrigerator Signals Cooling pipe Vacuum for thermal insulation Al Honeycomb Liq. Xe window PMT filler Plastic 1.5m LXe Calorimeter • ~800l liquid Xe (3t) • ~800 PMTs immersed in LXe • Only scintillation light detected • Fast response (45 ns decay time) • High light output (70% of NaI(Tl))1) • High uniformity compared with segmented calorimeters • High channel occupancy will be accommodated by special trigger scheme 1) T. Doke and K. Masuda, NIM A 420 (1999) 62 NOON 2000

g Response • Signal is distributed over many PMTs in most cases • Weighted mean of PMTs on the front face  dx ~ 4mm FWHM • Broadness of distribution  dz ~ 16mm FWHM • Timing resolution  dt ~ 100ps FWHM • Energy resolution ~ 1.4% FWHMdepends on light attenuation in LXe x z NOON 2000

Calorimeter Prototypes “Small” “Large” • 32 PMTs, 2.3 l LXe • Tested with radioactive sources 51Cr, 137Cs, 54Mn, 88Y • Extrapolated resolutions at 52.8 MeV in agreement with quoted numbers • 264 PMTs,150 l LXe • Assembly finished next January • Measure resolutions with 40 MeV photon beam at ETL, Tsukuba, Japan NOON 2000

Homogeneous Field Gradient Field (COnstant-Bending-RAdius) Positron Spectrometer e+ from m+e+g Ultra-Thin (~3g/cm2) superconducting solenoid with 1.2 T field NOON 2000

Drift Chamber • 16 radial chambers with 20 wires each • Staggered cells measure both position and time • He – C2H6 gas to reduce multiple scattering • Vernier pattern to determine z coordinate NOON 2000

Prototype Test at PSI • 0, 0.6, 0.8, 1T field • 3 tilting angles • Data analysis finished soon NOON 2000

Thin Superconducting Coil g Stopping Target Muon Beam Timing Counter e + Drift Chamber Positron timing counter • Aimed resolution ~100ps FWHM • Beam tests at KEK in July 1999 • Taken over by Pisa group • Scintillators ordered • Beam tests next spring NOON 2000

Kinematics qeg= 180° m g e g e + Ee = 52.8 MeV Eg = 52.8 MeV Trigger Requirements • Beam rate 108 s-1 • Fast LXe energy sum > 45MeV 2103 s-1 • g interaction point • e+ hit point in timing counter • time correlation g – e+ 200 s-1 • angular corrlation g – e+ 20 s-1 M.C. NOON 2000

BS S BS S >45MeV BS S BS AND . . . Max Max Df Max fe+ 10 stages = 1024 chn T[ns] 0 50 60 70..150 160 170 Baseline Subtraction - Trigger Implementation 100MHz 8-bit FADC FADC FPGA Trigger FADC SRAM . . . FADC FADC FADC FPGA FADC SRAM FADC … 800 channels NOON 2000

Analog Waveform Sampling Chip (DSC) 40MHz, 10 bit . . . FPGA 2.5GHz FADC SRAM VME Waveform Digitizing • Waveform Digitizing for all channels • Custom domino sampling chip (DSC) designed at PSI • Costs per DSC ~1US$ • 2.5 GHz sampling speed  40ps timing resolution • Sampling depth 1024 bins  400ns (100ns+300ns) • Readout electronics similar to trigger • Drift chamber signals go directly to FADC (100MHz) Previous Version 1.2 GHz C. Brönnimann et al., NIM A420 (1999) 264 NOON 2000

now Planning R & D Assembly Data Taking 1997 1998 1999 2000 2001 2002 2003 2004 2005 Time Table Conclusions • Preparations are going well in all areas of the experiment • Innovative technologies developed useful for other experiments • Next major milestone: Large prototype test in Tsukuba spring 2001 • Increasing support from PSI and Pisa • New collaborators are welcome http://meg.icepp.s.u-tokyo.ac.jp http://meg.pi.infn.it http://meg.psi.ch NOON 2000

A new m  e g experiment at PSI