Title: The MECO Experiment
1The MECO Experiment
- Coherent µ?e Conversion in the
- Field of a Nucleus
- P. Yamin, BNL
2MECO 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
3When 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.
4Limits 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 7.8 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.
5What might we expect?
Supersymmetry
Compositeness
Predictions at 10-15
Second Higgs
After W. Marciano
6Supersymmetry 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
7Previous 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.
8Backgrounds
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
9Backgrounds, 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
10The 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
11The 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.
12The 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
13MECO 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
14Meco 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
15Spectrometer 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.
16Where 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)
17Where are we? (RD)
Design and Prototype
- Water-cooled target prototype tested, but not in
beam. - Straw tracker prototypes, including electronics,
produced - alternative (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.
18Where 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.
19Where are we? (Magnet)
20Where are we? (magnet layout)
21Where are we? (superconducting Coils)
Coil build
SSC cable embedded in copper 7kA, 50µW/g
nuclear heating?
22Where are we? (magnet structural)
23Expected 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
24Expected 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
25History of Lepton Flavor Violation Searches
1
?- 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
26Where Will we be gt2008?
MECO will be a significant part of the 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