The MECO Experiment

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The MECO Experiment

• Coherent µ?e Conversion in the
• Field of a Nucleus
• P. Yamin, BNL

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MECO Collaboration

• Institute for Nuclear Research, Moscow
• V. M. Lobashev, V. Matushka,
• New York University
• R. M. Djilkibaev, A. Mincer,
  P. Nemethy, J. Sculli, A.N. Toropin
• Osaka University
• M. Aoki, Y. Kuno, A. Sato
• University of Pennsylvania
• W. Wales
• Syracuse University
• R. Holmes, P. Souder
• College of William and Mary
• M. Eckhause, J. Kane, R. Welsh

• Boston University
• J. Miller, B. L. Roberts, O. Rind
• Brookhaven National Laboratory
• K. Brown, M. Brennan, G. Greene,
• L. Jia, W. Marciano, W. Morse,
  Y. Semertzidis, P. Yamin
• University of California, Irvine
• M. Hebert, T. J. Liu, W. Molzon, J.
  Popp, V. Tumakov
• University of Houston
• E. V. Hungerford, K. A. Lan, L.
  S. Pinsky, J. Wilson
• University of Massachusetts, Amherst
• K. Kumar

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When a muon stops in matter, the principal
interactions are

• Capture on Nucleus µ-N(Z,A) ? ?µN(Z-1,A)
• Decay in Orbit µ- ? ?µe-?e

Coherent conversion is µ-N(Z,A) ? e-N(Z,A), and
the signal is a monoenergetic electron .
We will measure Rµe ?µ-N(Z,A) ?
e-N(Z,A)/ ?µ-N(Z,A) ? ?µN(Z-1,A) A single
event implies Rµe gt 2 ? 10-17.
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Limits on Lepton Flavor-Violating Processes
1. KL ? µe 4.7 x 10-12 D. Ambrose, et al.,
PRL 81, 5734 (1998) 2. KL ? p0µe 3.2 x
10-10 P. Krolek, et al., Phys Lett. B 320, 407
(1994) 3. K ? p µe 2.1 x 10-10 A. M. Lee,
et al., PRL 64, 165 (1990) 4. µ ? eee-
1.0 x 10-12 U. Bellgardt, et al., Nucl. Phys
B299, 1 (1999) 5. µ ? e? 1.2 x 10-11 M.
L. Brooks, et al., PRL 83, 1521, (1999) 6.
µ-N ? e-N 6.1 x 10-13 F. Riepenhausen, in
Proceedings of the Sixth

Conference on the Intersections of Particle

and Nuclear Physics, T.W.
Donnelly, ed.
(AIP,
New York, 1997), p. 34.
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What might we expect?
Supersymmetry
Compositeness
Predictions at 10-15
Second Higgs
After W. Marciano
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Supersymmetry Predictions for m ? e

• From Hall and Barbieri
• Large t quark Yukawa couplingsimply observable
  levels of LFV insupersymmetric grand unified
  models
• Extent of lepton flavor violation in
  Supersymmetry related to quark mixing
• Other diagrams calculated by Hisano, et al.

Process Current Limit SUSY level
10-12 10-15
10-11 10-13
10-6 10-9
R?e
MECO single event sensitivity
100 200
300 100 200
300
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Previous ExperimentSINDRUM II
1.2 ? 107 µ-/sec 6 ? 105 p-/sec 2.4 ?103 e-/sec
Prompt backgrounds removed by timing, but we want
to increase beam intensity by a factor of
1000. ?pulsed beam.
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Backgrounds
1. Muon Decay in Orbit EmaxEconversion, when ?s
carry no energy. dN/dEe ? (Emax
E)5 Resolution 900 keV FWHM 2. Radiative µ
Capture, µ-N(Z) ? ??N(Z-1)? For Al, E?max
102.5 MeV/c2, P(E?gt 100.5 MeV/c2) 4 x 10-9 P(?
? ee-, Eegt100.5 MeV/c2)2.5 x 10-5
Endpoint in Al 105.1 MeV/c2
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Backgrounds, contd.
3. Radiative p Capture P(E?gt105 MeV/c2)
0.01 P(??ee-, 103.5ltEelt100.5 MeV/c2)3.5 ?
10-5 beam extinction lt10-9 4. µ Decay in Flight
and e- Scatter in Stopping Target beam
extinction 5. Beam e- Scattering in Stopping
Target beam extinction 6. Antiproton Induced e-
thin stopping window 7. Cosmic Ray Induced e-
active and passive shielding
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The MECO Apparatus
Straw Tracker
Muon Stopping Target
Muon Beam Stop
Superconducting Transport Solenoid
(2.5 T 2.1 T)
Crystal Calorimeter
Superconducting Detector Solenoid (2.0 T
1.0 T)
Superconducting Production Solenoid (5.0
T 2.5 T)
Muon Production Target
Collimators
Proton Beam
Based on MELC design 4 x 1013 incident p/sec
1 x 1011 stopping µ/sec
Heat Radiation Shield
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The MECO Proton Beam
Pulsed beam from AGS to eliminate prompt
backgrounds
Two of six rf buckets filled, giving 1.35 µsec
separation between pulses for a 2.7 µsec rotation
time. AGS cycle time is 1 sec. Extinction must
be gt109 fast kicker in transport will divert
beam from production solenoid extinction can be
monitored. Theres work to be done. 2 ? 1013
protons/bucket is twice the present AGS bunch
intensity. In preliminary tests, extinctions of
107 have been achieved.
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The MECO Muon Beam Transport Solenoid
stopping target
Sign and momentum select in curved solenoid
section. (Curvature eliminates direct photon
transport.) Collimators absorb antiprotons,
low momentum and positive particles.
µ spectrum
stopping µ spectrum
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MECO Detector Solenoid

• Graded field in front section to increase
  acceptance and reduce cosmic ray background
• Uniform field in spectrometer region to minimize
  corrections in momentum analysis
• Tracking detector downstreamof target to reduce
  rates

1T
Electron Calorimeter
1T
Tracking Detector
2T
Stopping Target 17 layers of 0.2 mm Al
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Meco Detector Elements
Magnetic spectrometer measures electron momentum
with precision of 0.3 (rms)essential to
eliminate decay in orbit background. Consists of
2800 axial straw tube detectors 2.6 m x 5 mm.
250 µm wall thickness. 2000 element PbWO4 (3 x
3 x 12 cm) calorimeter measures electron energy
to 5, providing trigger and confirming
trajectory.
Electron starts here.
Position resolution 0.2 mm transversely, 1.5 mm
axially
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Spectrometer Performance
55, 91, 105 MeV e- from target

• Performance calculated using Monte Carlo
  simulation of all physical effects
• Resolution dominated by multiple scattering in
  tracker
• Resolution function of spectrometer convolved
  with theoretical calculation of muon decay in
  orbit to get expected background.

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Where are we? (Funding)
RSVP is in NSF budget, beginning in FY06 MECO
represents about 60 of its capital cost.
NSF FY04 budget submission
I can say that RSVP is now the highest priority
construction project from the division of
Mathematical and Physical Sciences. (R.
Eisenstein to J. Sculli, 1/29/02)
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Where are we? (RD)
Design and Prototype

• Water-cooled production target prototype tested,
  but not in beam.
• Longitudinal straw tracker prototypes, including
  electronics,
• produced transverse tracker design under
  consideration.
• Prototyping of PbWO4 calorimeter, including APD
  readout.
• Cosmic ray shield scintillator prototypes.
• With additional RD support, AGS beam studies
  and design for
• rf modulated magnet.
• Conceptual design study for solenoids completed
  by MIT PSFC
• soliciting bids for full engineering design.

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Where are we? (Calorimeter, Straws)
3 x 3 x 14 cm PbWO4 crystal (NYU)
13 x 13 mm RMD APD and 5 x 5 mm Hamamatsu APD
First full-length vane prototype (Houston)
Seamless straws (Osaka) 25 µm thick 5 mm
diameter polyamide and carbon
Tests in freezer with cosmic ray muons indicate
calorimeter resolution at 105 MeV is 3.3.
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Where are we? (Magnet)
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Where are we? (magnet layout)
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Where are we? (superconducting Coils)
Coil build
SSC cable embedded in copper 1.5-4.0 kA, lt 20
µW/g nuclear heating?
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Where are we? (magnet structural)
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Expected Sensitivity of the MECO Experiment

• We expect 5 signal events for 107 s (2800
  hours) running if Rme 10-16

Contributions to the Signal Rate Factor
Running time (s) 107
Proton flux (Hz) (50 duty factor, 740 kHz micropulse) 4 ?1013
m entering transport solenoid / incident proton 0.0043
m stopping probability 0.58
m capture probability 0.60
Fraction of m capture in detection time window 0.49
Electron trigger efficiency 0.90
Fitting and selection criteria efficiency 0.19
Detected events for Rme 10-16 5.0
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Expected Background in MECO Experiment

• We expect 0.45 background events for 107 s
  running with sensitivity of 5 signal events
  for Rme 10-16

Source Events Comments
m decay in orbit 0.25 S/N 20 for Rme 10-16
Tracking errors lt 0.006
Radiative m decay lt 0.005
Beam e- lt 0.04
m decay in flight lt 0.03 Without scattering in stopping target
m decay in flight 0.04 With scattering in stopping target
p decay in flight lt 0.001
Radiative p capture 0.07 From out of time protons
Radiative p capture 0.001 From late arriving pions
Anti-proton induced 0.007 Mostly from p-
Cosmic ray induced 0.004 Assuming 10-4 CR veto inefficiency
Total Background 0.45 Assuming 10-9 inter-bunch extinction
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History of Lepton Flavor Violation Searches
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?- N ? e-N ? ? e? ? ? e e e-
10-2
10-4
10-6
10-8
10-10
10-12
K0?? ?e- K?? ? ?e-
SINDRUMII
10-14
10-16
MECO Goal ?
1940 1950 1960 1970
1980 1990 2000 2010
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Where will we be gt2008?
MECO will be a significant part of the
accelerator- based US High Energy physics program
towards the end of this decade!
http//meco.ps.uci.edu
Bill Marciano at annual BNL/HEP Review, 4/03