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Precision Measurement of Muon Capture on the Proton“Cap experiment”
- + p + n
www.npl.uiuc.edu/exp/mucapture/
Cap @ PSI
Supported byPaul Scherrer Institute, Russian Ministry of Science and Technology, US National Science Foundation,US Department of Energy, University of Illinois, Civilian Research Development Foundation and INTAS.
collaborationV.A. Andreev, A.A. Fetisov, V.A. Ganzha, V.I. Jatsoura, A.G. Krivshich, E.M. Maev, O.E. Maev,
G.E. Petrov, S. Sadetsky, G.N. Schapkin, G.G. Semenchuk, M. Soroka, A.A. Vorobyov Petersburg Nuclear Physics Institute (PNPI), Gatchina 188350, Russia
P.U. Dick, A. Dijksman, J. Egger, D. Fahrni, M. Hiltebrandt, A. Hofer, L. Meier, C. Petitjean, R. Schmidt
Paul Scherrer Institute, PSI, CH-5232 Villigen, Switzerland
T.I. Banks, T.A. Case, K.M. Crowe, S.J. Freedman, B. Lauss University of California Berkeley, UCB and LBNL, Berkeley, CA 94720, USA
K.D. Chitwood, S. Clayton, P. Debevec, F. E. Gray , D. W. Hertzog, P. Kammel, B. Kiburg, C. J. G. Onderwater, C. Ozben, C. C. Polly, A. Sharp
University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
L. Bonnet, J. Deutsch, J. Govaerts, D. Michotte, R. Prieels Université Catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium
R. M. Carey. J. PaleyBoston University, Boston, MA 02215, USA
T. Gorringe, M. Ojha, P. Zolnierzcuk University of Kentucky, Lexington, KY 40506, USA
F.J. Hartmann Technische Universität München, D-85747 Garching, Germany
Cap
Scientific case: +p capture
capture probes axial structure of nucleon
capture decay
hadronic vertex dressed by QCD q2 dependent form-factors
dual role of
• acts as well defined probe of hadronic structureQCD tests, pseudoscalar form-factor gP, chiral symmetry
• Standard Model symmetries of lepton-quark interaction
pn
e
e-
n
p
-
W W
- + p + n
Cap
Nucleon charged current at q2= - 0.88 m2
J = V - A
VgV(q2) + igM(q2)/2M q + gS(q2)/m q
AgA(q2) + gP(q2) q/m + igT(q2)/2M q
• Vector current in SM determined via CVC gV(0)=1, g(q2)=1+q2 r2/6, rV
2=0.59 fm2
gM(0)=p-n-1=3.70589, rM2=0.80 fm2
q2 dependence from e scatt.
• Axial vector FF from experiment gA(0)=1.2670(35), rA
2=0.42±0.04 fm2 q2 dependence from quasi-elastic scattering, e-production
• 2nd class FF gS, gT forbidden by G symmetry, e.g. gT/gA=-0.15 ±0.15 (exp), -0.0152 ±0.0053(QCD sum rule, up-down mass difference)
• error fromVud = 0.16 %
nucleon weak formfactors gV,gM,gA
• determined by SM symmetries and data
• contribute <0.4% uncertainty to S
gV = 0.9755(5)
gM = 3.5821(25)
gA = 1.245(3)
remains
gP = ?Cap
pseudoscalar form factor gP
PCAC:
gP=8.7
heavy baryon chiral perturbation theory:
gP=(8.74 0.23) – (0.48 0.02) = 8.26 0.23gNN
13.31(34)13.0(1)
13.05(8)
calculations O(p3) show good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO
author year gP
S
T comment
Primakoff 1959 smaller gA
Opat 1964 smaller gA
Bernard et al 1994 8.44(23)Fearing et al 1997 8.21(9)
Govaerts et al 2000 8.475(76) 688.4(38) 12.01(12)Bernard et al 2000/1 687.4 (711*) 12.9 NNLO, small scaleAndo et al 2001 695 (722*) 11.9 NNLO
n
p
-
gNN
F
*NLO result
fundamental and least known weak nucleon FF solid theoretical prediction at 2-3% levelbasic test of QCD symmetries
Recent reviews:T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1
fundamental and least known weak nucleon FF solid theoretical prediction at 2-3% levelbasic test of QCD symmetries
Recent reviews:T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1
Cap
Experimental information on gP
Ordinary Muon Capture - + p + n
Radiative Muon Capture - + p + n +
BR~10-3, 8 experiments 1962-82, BC, neutron, electron detection “in principle” most direct gP measurement
BR~10-8, TRIUMF (1998), E>60 MeV, 297 ± 26 eventscloser to pion pole 3x sensitivity of OMC
theory more involved (min substitution, ChPT)
• Muon capture in nuclei
+ 3He + 3H st=1496 ±4 s-1 PSI (1998) gp=gp
th (1.08 ±0.19) error dominated by 3-N theory
correlation measurements
• Neutrino scattering
• electro production at thresholdCap
experimental challenges
e+e+
- p () + n p
(Rich) physics effects
• Interpretation: where does capture occur ?
Critical because of strong spin dependence of V-A interaction
• Background: Wall stops and diffusion Transfer to impurities p+Z Z +p
• Rate and statistics (BR = 10-3)
• SR effect for +
TS
pp
pp
pp
ortho
para
F=0 F=1
J=1
J=0
OP
n+
n+
n+
Cap
Muon Capture and gP
20 40 60 80 100 120
2.5
5
7.5
10
12.5
15
17.5
20
ChPT
OP (ms-1)
g P
RMC
Cap proposed
exp theory
OMC Saclay
update from Gorringe & Fearing
Interpretation of observed rate sensitive to pp state, where capture occurs, atomic physics
• OMC not precise, ambiguous interpretation
• RMC 4discrepancy exp/th
• no overlap theory & OMC & RMC
• OMC not precise, ambiguous interpretation
• RMC 4discrepancy exp/th
• no overlap theory & OMC & RMCCap
Cap experimental strategy New idea: active target of ultra-pure H2 gas 10 bar measure +
and - S = 1/- - 1/+ , to 10-5
New idea: active target of ultra-pure H2 gas 10 bar measure +
and - S = 1/- - 1/+ , to 10-5
TPC
ePC1
ePC2
eSCe
Cap
experimental strategy
Physics
• Unambigous interpretation At low density (1% LH2) mostly capture from p(F=0) atomic state.
• Clean muon stop definition: Wall stops and diffusion eliminated by 3-D muon tracking
• In situ gas impurity control (cZ<10-8, cd<10-6) hydrogen chambers bakeable to 150 C, continuous purification TPC monitors capture on impurity and transfer to deuterium 10-8 sensitivity with gas chromatograph
• +SR: calibrated with tranverse field 70 G
Statistics
• 1010 statistics: Complementary analysis methods
ppP
ppO
p
pp
ppP
ppP
ppO
ppO
time (s)
100% LH2 1 % LH2 10% LH2
Cap
- +
transfer to deuterium, diffusion
p+d d + pRamsauer Townsend minimum in d + p scattering at 1.6 eVdiffusion
catalyzed pd fusion
d + p pd (5.3MeV)+3He(0.2KeV)
Cap
Gas purification and analysis
Hydrogen purification and analysis to better than 10-8
• Electrolytic generator purity ~0.3 ppm
• Pd filter cleaning from O2 and N2 to better 10-8 directly verified.
• TPC gas purity deterioration can be reduced by longer conditioning after N2 filling. Continuous purification system under construction.
• Different methods of D2 diagnostic indicate isotopic purity at 1 ppm level, further effort in production and monitoring required for sub ppm level.
Cap
Cap status and plans
Planned schedule Cap I
• technical proposal spring 2001, received “high priority status”
• development final detector components and high purity chambers, 2001-2002
• commissioning fall 2002, spring 2003
• data run 2003, 2004 (S 3%, 1%)
Cap II with muon-on-request beam* (2004, 2005)chopper development and + result from Lan
• goal S to 0.3 %, gP 2-3%
20-30x exp improvementS similar precision as n
exp challenges: statistics, purity, atomic physics
*P.K. et al, PSI letter of intent 1998Cap
Scientific Context
muon capture on proton - + p + n
to 1 %
muon capture on proton - + p + n
to 1 %
Nucleon form factors, chiral symmetry of QCD
Cap experimentgP to < 7% (3% with Lan kicker)
muon decay+ e++e+
+ to 1 ppm
muon decay+ e++e+
+ to 1 ppm
Fermi Coupling Constant
Lan, FAST experiment
GF to < 1ppm
muon capture on deuteron
- + d + n +n
to 1 %
muon capture on deuteron
- + d + n +n
to 1 %
Basic EW two nucleon reaction, calibrate v-d reactions
D project
Cap
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