The MECO Experiment

1
The MECO Experiment

• Coherent µ?e Conversion in the
• Field of a Nucleus
• P. Souder, Syracuse University

2
Outline

• A Bit of History
• Theoretical Motivation for Sensitive Lepton
  Flavor Violation Search Experiments ala MECO
• The MECO Experimental Apparatus
• Expected Sensitivity and Backgrounds
• Status and Outlook

3
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
• Syracuse University
• R. Holmes, P. Souder
• College of William and Mary
• M. Eckhause, J. Kane, R. Welsh

• Boston University
• J. Miller, B. L. Roberts
• Brookhaven National Laboratory
• K. Brown, M. Brennan, G. Greene,
• L. Jia, W. Marciano, W. Morse,
  Y. Semertzidis, P. Yamin
• University of California, Irvine
• C. Chen M. Hebert, 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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The First ?-N ? e-N Experiment

• After the discovery of the muon, it was realized
  it could decay into an e g or convert to an
  electron in the field of a nucleus
• Without flavor conservation, the expected
  branching fraction for ??e? is about 10-5.
• Steinberger and Wolf looked for ?-N ? e-N in
  1955, publishing a
  
  null result with a limit
  
  
  of R?e lt 2 ? 10-4

Absorbs e- from ?- decay
Conversion e- reach this counter
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SINDRUM II m-N ? e-N Limit
Lessons learned from SINDRUM II drive much of the
design of the MECO beam and experimental apparatus
SINDRUM II has thebest limit on this process
Prompt Background
Cosmic RayBackground
Expected Signal
Muon Decay in Orbit
Experimental signature is 105 MeV e- originating
in a thin stopping target
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Limits on Lepton Flavor-Violating Processes
1. KL ? µe 3.4 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.
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History 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
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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.

R?e
MECO single event sensitivity
100 200
300 100 200
300
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What might we expect?
Supersymmetry
Compositeness
Predictions at 10-15
Second Higgs
After W. Marciano
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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 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 X 1013
protons/bucket is twice the present AGS bunch
intensity. In preliminary tests, extinctions of
107 have been achieved.
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Features of the MECO Experiment

• 1000fold increase in m beam intensity over
  existing facilities
• High Z target for improved pion production
• Axially-graded 5 T solenoidal field to maximize
  pion capture

Superconducting Solenoids
Muon Beam
1 T
1 T
Calorimeter
2 T
Straw Tracker
Stopping Target Foils
Proton Beam
2.5 T

• Curved transport selects low momentum m-
• Muon stopping target in a 2 T axially-graded
  field to improve
  conversion e- acceptance
• High rate capability electron detectors in a
  constant 1 T field

5 T
Pion Production Target
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Production Region

• Axially graded 5 T solenoid captures pions and
  muons, transporting them toward the stopping
  target
• Cu and W heat and radiation shield protects
  superconducting coils from effects of 50kW
  primary proton beam

Superconducting coils
2.5 T
Proton Beam
Production Target
Heat Radiation Shield
5 T
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Transport Solenoid

• Curved solenoid eliminates
  line-of-sight transport of photons
  and neutrons
• Curvature drift and collimators sign and momentum
  select beam
• dB/ds lt 0 in the straight sections to avoid long
  transit time trajectories

2.1 T
Collimators
2.5 T
Curvature Drift
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Detector Region

• Axially-graded field near stopping target to
  increase acceptance and reduce cosmic ray
  background
• Uniform field in spectrometer region to simplify
  momentum analysis
• Electron detectors downstream of target to reduce
  rates from g and neutrons

Electron Calorimeter
Straw Tracking Detector
Stopping Target Foils
1 T
1 T
2 T
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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. 25
µm wall thickness. 1200 element PbWO4 (3.5 x
3.5 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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Expected Sensitivity of the MECO Experiment

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

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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

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Where 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.
  

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Design of the MECO Magnets
The superconducting solenoids define the critical
path for MECO

• Very detailed CDR completed (300 pages)
• Complete 3D drawing package
• Technical Specification and SOW for commercial
  procurement being prepared
• Industrial manufacturability studies completed
• Interface engineering ongoing as funds allow

• 5 T maximum field
• 150 MJ stored energy
• Uses surplus SSC cable
• Within industry capabilities

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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? (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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RSVP Status

• Scientific Approval
• Approved by BNL and by the NSF through level of
  the Director
• Approved by the NSB as an MREFC Project
• Endorsed by the HEPAP Subpanel on long-range
  planning
• Technical and Management Reviews
• Positively reviewed by several NSF and Laboratory
  appointed panels
• MECO magnet system design positively reviewed by
  external expert committees appointed by MECO
  leadership
• Funding
• Currently operating on RD funds from the NSF
• RSVP is in the Presidents FY05 budget, efforts
  in Congress are ongoing
• Schedule
• NSF funding profile shows a five-year
  construction plan completing in FY10
• NSF will provide incremental operations support
  above that needed for AGS operations in support
  of RHIC

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PRIME at PRISM at J-PARC

• Phase Rotation Intense Slow Muon Source
• Central kinetic energy 20 MeV (p68 MeV/c)
• Kinetic energy spread 0.5-1.0 MeV
• Beam repetition 1 kHz
• Pulsed beam (gt1 kHz)
• Energy spread allows thin stopping target
• Better e- resolution and acceptance
• Intensity 1011-1012 m /sec
• Less scattering background
• Less beam contamination
• No p contamination due to 150 m FFAG flight path
• Kicker into FFAG improves beam extinction
• No high energy e
• Instantaneous detector rates might be a challenge
• Goal is to to J-PARC achieve Rme lt 10-18

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Outlook

• The physics potential for MECO and experiments
  like it is robust and compelling. Recent results
  have pushed to new levels of sensitivity without
  observing new physics
• New experiments are working to improve by several
  more orders of magnitude, reaching levels where
  signals are expected.
• MECO expects to move into the detailed design
  phase very soon, meaning now is the perfect time
  for people to get involved!

SINDRUM2
MECO (2010)
PRIME (?)