Search for the Lepton-Flavour Violating Decay m

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Search for the Lepton-Flavour Violating Decaym
e g Presented by Peter-Raymond Kettle
(PSI)on behalf of the MuEGamma
Collaboration6th International WorkshopHeavy
Quarks and LeptonsVietri s/m, Salerno,
Italy27th May 1st June 2002
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Physics Motivation

• Minimal Standard Model (SM)-
• Baryon Number, Lepton Flavour Lepton Number -
  conserved !
• neutrinos massless - no oscillations !
• Hence processes such as ??e?, ?? e, ?? eee,
  K0L??e, Z0??e ?-oscillations
• 0???-decay are sensitive tools to probe
  physics beyond the Standard Model
• Discovery of ?-oscillations (Super-K)
• g-2 Results (BNL)
• Evidence for 0???-decay (Heidelberg/Moscow)
• Proton Decay ??? (Kolar Goldfield)
• Extensions to SM -( with ?-oscillations) -
  Predict LFV rates too small to be observed
• Extensions beyond SM - Predict LFV BNV at a
  measurable level
• (e.g. see Barbieri Hall, Hisano et al.)
• Super Symmetry (SUSY-GUTs)
• SU(5) 10-13lt Br( meg) lt 10-15
• SO(10) 10-11lt Br( meg) lt 10-13
• !!! Just below Present Experimental Bound
  lt1.210-11 !!!

Further Stimulate the search for LFV in the
charged Lepton Sector
?? ? e ?
? ? ? ?
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Physics Motivation cont.
e.g. Prediction Br(??e?) vs. parameter space in
SUSY SU(5) see J. Hisano et al. Phys. Lett. B391
(1997) 341
MuEGamma Goal 10-14
Similar plots for ?? e conversion with R?e-
ranging between (10-14 - 10-17) over
most of the parameter ranges MECO(BNL)-goal
single event sensitivity of 2.10-17
tan(?) - ratio of vac. expec. values of Higgs
Fields ? - Higgs Fields mixing parameter
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Physics Motivation cont.
Mega Limit
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Experimental Chronology

• Experimental LFV-Searches have a Long History -
• goes back to 1947 E. P. Hincks B. Pontecorvo,
  using cosmic rays (??e?)
• Improvement about 2-Orders of Magnitude per
  Decade
• muons seem to provide the most sensitive limits
  (copious source, small mass, long life)
• Most Promising Candidates in the Charged Lepton
  Sector ?? e? ? ?? e

MEG(LAMPF) M.L. Brooks et al BR(??e?)lt 1.210-11
SINDRUM II (PSI) BR(??e)lt 6.110-13
Present Generation
Next Generation
PRIME(JAERI) Sensitivity 10-18
MuEGamma(PSI) Sensitivity 10-14
MECO(BNL) Sensitivity 210-17
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?? e? Chronology

• End of 70s Meson Factories take over
• competition
• higher intensity beams
• Duty cycle

PSI LOI 1998 Proposal 1999 Approval 1999
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PSI LFV
PSI also has a tradition in LFV-searches
PSI
Present most Sensitive Measurements
Reaction 90 CL
Br(?-Au?e-Au) New Prelim.
Br(?-Ti?e-Ti) 6.110-13
Br(??ee-e) 110-12
Br(?-Pb?e-Pb) 4.610-11
Br(?-S?e-S) 710-11
PMM(??e-? ?-e) 8.310-11
Br(?-Ti?eCa) 1.710-12
Br(?-S?eSi) 910-10
Paul Scherrer Institute
Sindrum II-Collab. M M- Collab. SIN-measurements

• 600 MeV Ring Cyclotron
• 1.8-2mA Proton Current
• DC Beam 100 Duty Cycle
• ?E5 Surface Muon Beam gt108?s-1

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Latest on (? ?Au ? e ?Au ) from Sindrum II
Coherent ?-less conversion of ??e in a
Muonic Atom

• muon stops in matter, forms muonic atom
• muon cascades to 1S-state lt10-16s
• coherent interaction with nucleus ( left in
• ground state) converts to electron without ?s
• Conversion Energy Ee M?-B?-RAu? 95.55227 MeV
• However- more often
• captured
• on nucleus
• or
• Decays in a
• Coulomb-bound orbit (MIO)

Hence Signature Single Electron of 96MeV

• Experimental Backgrounds
• ?-decay in orbit (MIO)
• Emax E?e dN/dE ? (Emax-Ee)5
• (ii) Radiative Muon Capture(RMC)
• E? E?e 0.7 MeV
• (iii) Radiative Pion Capture(RPC)
• E? lt130MeV (lt2)
• (iv)Cosmics induced es (tracking)

• Why Gold?
• Linear rise of Conversion Probability predicted
• for heavy elements
• Lightweight Construction (background)
• Single Isotope (good for ??e Search)

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Sindrum II ??e Conversion on Gold

• 52 MeV/c ?? beam
• ???-separation beg. PMC 8.5m
• ?? stop in 40micron Au Tg.
• e? tracked Hodo. Cerenkov
• DCs
• ??Au X-rays Ge for Norm.
• No Signal Observed !

Expected Signal at 5x10-12
Preliminary ! ! !
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New ??e? Experiment at PSI
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??e? Experimental Principle

• Basic Requirements
• High stop-density (rate) m -beam with high duty
  factor (accidentals)
• High resolution g-detection (angle energy,
  accidentals)
• Solenoidal magnetic spectrometer
  (p-determination)
• Fast, high resolution tracking chambers for e
  momentum determination (p- angle)
• Timing counter for e (angle time)

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Beam Transport System
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Detector Overview Required Performance

• Simulated Performance FWHM
• DEe 0.7
• DEg 1.4 2.0
• Dqeg 12 14 mrad
• Dteg 150 ps

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Photon Detection
Detector requirements Excellent energy-,
timing-, and position resolutions
Liquid Xenon Scintillation Detector
Mass number 131.29
Density 3.0 g/cm3
Boiling/ melting points 165 K 161 K
Energy per photon 24 eV
Radiation length 2.77 cm
Decay time (fa) (slow) (recombi.) 4.2 nsec 22 nsec 45 nsec
Scintillation light ? 175 nm
Refractive index 1.57 1.75
NaI too slow CsI BGO poor ?E/E at 52.8
MeV In homo. coverage
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Small Prototype Calorimeter

• Total 32 x PMTs
• Active Xe volume
• 116 x 116 x 174 mm3 (2.3liter)
• Energy-, Position-, and Timing resolution
  measured for
• gammas up to 2MeV

• Simple extrapolation to 52.8 MeV
• gammas implies
• senergy 1,
• sposition a few mm,
• stime 50psec
• To be tested with Large Prototype

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Large Prototype LXe Calorimeter
Final Performance Parameters to be
achieved lateral ?x4mm, depth ?z16 mm ?E
1.4 , ?t 100 ps all FWHM

• Currently
• construction finished
• 228 PMTs
• 69 litres LXe
• cryogenics working well
• initial beam test 40 MeV
• gammas at AIST Tsukuba
• cosmic ray measurements

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Positron Detection

• COBRA Spectrometer (Constant Bending Radius)
• Thin superconducting magnet with gradient field
• Drift chambers for positron tracking
• Scintillation counter arrays for positron timing
  triggering

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Positron Spectrometer COBRA
therefore easy to look
for Large Radius Tracks i.e. fixed PTOT
e from meg
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COBRA Magnet

• Cable Fabricated
• Winding Started
• Cryostat construction
• Assembly by End of 2002

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Positron Tracking Drift Chambers
Drift-cell Structure
z-determination

• 16 planar chambers with each 18 sense-wires
• aligned radially at 10 intervals
• Staggered cells measure both position r µ (t1-t2)
  sr200 mm and time t µ (t1t2)/2 st5 ns
• He C2H6 gas to reduce multiple scattering
• Vernier pattern to determine z-coordinate
• sz 300 mm

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Positron Timing Counters
Hodoscope Layout
Cosmic Ray Test
CORTES Facility INFN Pisa

• Scintillator bar
• (5cm x t1cm x 100cm long)
• Telescope of 8 x MSGC

• Measured resolutions
• stime60psec independent of incident position
• stime improves as 1/vNpe

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Trigger

• ?-stopping rate
  108 s-1
• Fast LXe energy sum ??? gt 45MeV
  2?103 s-1
• time correlation g e
  200 s-1
• g interaction point (PM with Qmax on front face
  only)
• extrapolate to target centre correlate
  with
• e impact point on timing counter
• angular corrlation g e
  20 s-1
• cut on Rmax of drift chambers ?
  10 s-1

Photon direction selection in ? for a meg
event ( PMT with QMAX ) gives
a 7.5º spread (5 counters) in the e- timing
counters (one coloured band)

• Digital Trigger
• 2GHz Waveform digitization
• 100 MHz FADCs FPGAs
• baseline subtraction
• QT-Alogorithm (Qmax t)
• latency 350 ns

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Conclusions
Recent Experiments have improved LFV limits in
the charged sector Still NO Signal Found !
??e? at 10-13 level
MEGA
Sindrum II
New Experiments plan to improve Single Event
Sensitivities gt 103
MuEGamma
MECO
Simulation HOPEFULLY REALITY !
With LFV results from neutrino sector Prospects
for signature of New Physics e.g. SUSY-GUT good !
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Timescale

• All Detector Systems under development
• RD phase still in progress
• Next significant Milestone Large Prototype test
• Beam studies PSI ??? planned for 2002

Further interest
http//meg.icepp.s.u-tokyo.ac.jp http//meg.pi.inf
n.it http//meg.psi.ch