muegamma

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

Physics Motivation: 

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

Prediction from SUSY SU(5): 

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

Connection with n oscillations1): 

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

Previous m+  e+ g Experiments: 

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

MEG Collaboration: 

MEG Collaboration 35 7

Experimental Method: 

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+

Signal and Background: 

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 e g n n m g men + g e m

m  e g Signature: 

m  e g Signature  eg Ee,Eg = 52.8MeV  egnn Ee,Eg < 52.8MeV

Sensitivity and Background Rate: 

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

Paul Scherrer Institute: 

Paul Scherrer Institute Experimental Hall

Experimental Hall: 

Experimental Hall

Sindrum II @ PSI: 

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

pE5 Beam Line: 

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

Detector: 

Detector

LXe Calorimeter: 

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

g Response: 

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% FWHM depends on light attenuation in LXe x z

Calorimeter Prototypes: 

Calorimeter Prototypes 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 “Small” “Large” 264 PMTs, 150 l LXe Assembly finished next January Measure resolutions with 40 MeV photon beam at ETL, Tsukuba, Japan

Positron Spectrometer: 

Positron Spectrometer e+ from m+e+g Ultra-Thin (~3g/cm2) superconducting solenoid with 1.2 T field

Drift Chamber: 

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

Prototype Test at PSI: 

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

Positron timing counter: 

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

Trigger Requirements: 

Trigger Requirements M.C.

Trigger Implementation: 

Trigger Implementation FADC 100MHz 8-bit FPGA FADC FADC FADC SRAM Trigger FADC FPGA FADC FADC FADC SRAM … 800 channels . . .

Waveform Digitizing: 

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

Time Table: 

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