Precision Measurement of Muon Capture on the Proton

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Precision Measurement of Muon Capture on the
ProtonmCap experiment
?- p ? ?m n
Steven Clayton APS April Meeting May 2, 2004
Petersburg Nuclear Physics Institute (PNPI),
Gatchina,Russia Paul Scherrer Institut, PSI,
Villigen, Switzerland University of California,
Berkeley, UCB and LBNL, USA University of
Illinois, Urbana-Champaign, USA Universite
Catholique de Louvain, Belgium TU
Munich,Garching, Germany Boston University,
USA University of Kentucky, USA
_at_ PSI
mCap
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Muon Capture and gP
gP
update from Gorringe Fearing
RMC
ChPT?
mCap expected error
OMC Saclay
Saclay exp
theory
lOP (ms-1)
precise QCD (ChPT prediction) no overlap theory
OMC RMC
3
experimental challenges
m- ? ene?m
?- p (??) ? ?m n
p

• (Rich) physics effects
• Interpretation where does capture occur ?
• Critical because of strong spin dependence of
  V-A interaction

m
LS
LT
pm
pm
nn
F0
F1
Lortho

• Background Wall stops and diffusion
  Transfer to impurities mpZ ? mZ p
• Rate and statistics (BR 10-3)
• mSR effect for m

ppm
nn
J1
Lpara
ppm
nn
J0
mCap
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mCap Experimental Strategy I

New idea active target of ultra-pure H2 gas 10
bar measure t? and t?- ?
?S 1/??- - 1/?? , tm to 10-5

• Lifetime or Disappearance Method

Our experiment observes e and e decay products.
Muon capture reduces the µ lifetime compared
to the µ lifetime by 0.15 !
log(counts)
ePC2
1010events
µ
ePC1
µ
TPC
time
High precision measurement of the lifetime
difference
e
eSC
mCap
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mCap Experimental Strategy II

• Physics
• Unambiguous interpretation At low density (1
  LH2) mostly capture from mp(F0) atomic
  state.
• Clean muon stop definition Wall stops and
  diffusion eliminated by 3-D muon tracking
• In situ gas impurity control (cZlt10-8, cdlt10-6)
  hydrogen chambers bakeable to 150 C,
  continuous purification TPC monitors impurities
  in-situ 10-8 sensitivity with gas
  chromatograph
• mSR calibrated with transverse field 70 G

100 LH2
1 LH2
ppmO
pm
ppmP
ppmO
pm
ppmP
time (ms)

• Statistics
• 1010 decay events Complementary analysis
  methods

mCap
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mCap Experimental Setup
Key ideas active target of ultra-pure H2 gas
10 bar for muons, separate
large tracking detector for electrons.
Scintillator (t 0)
Time Projection Chamber (target)
Muon Detectors
Wire Chambers
µ
Wire Chambers
Electron Detectors
Hodoscope
mCap
e
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The Time Projection Chamber tracks muon stops in
3D.
p
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Event Display
m Stop
Beam View
Side View
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Impurity Monitoring
Impurity Capture
m Stop
Beam View
Side View
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mCap Time Projection Chamber in Clean Room
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2003 Run
Assembly March ? August Data-Taking
September ? mid-October.
commissioning / first physics
mCap
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Time Spectra 2003
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mCap Status and Plans

• 2003 Commissioning Run
• achieved high purity
• 109 m- events in 2 weeks
• analysis of data to get LS to 4 by end of 2004
• 2004 Upgrades
• install 2nd electron wire chamber
• install gas recirculation system
• The Fall 2004 Production Run should collect 1010
  m events and 1010 m- events, giving LS to 1.

mCap Collaboration Website www.npl.uiuc.edu/exp/m
ucapture/
Steven Clayton smclayto_at_uiuc.edu
mCap
14
Muon Capture and gP
gP
update from Gorringe Fearing
RMC
ChPT?
mCap expected error
OMC Saclay
TRIUMF exp, 2004
Saclay exp
theory
lOP (ms-1)
precise QCD (ChPT prediction) no overlap theory
OMC RMC
15
mCap experimental setup
Key ideas active target of ultra-pure H2 gas
10 bar for muons, separate
large tracking detector for electrons.
mSC (t 0)
mPC1
Muon Detectors
mPC2
TPC
µ
Electron Detectors
ePC1
eSC (Hodoscope)
ePC2
mCap
e
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Event Display
Strips
x direction
m Stop
Anodes
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Impurity Monitoring
Strips
x direction
Impurity Capture
m Stop
Anodes