Precision Measurement of Muon Capture on the Proton “  Cap experiment”  - + p   + n  PSI Supported by Paul 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.

collaboration V.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 , 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. Paley Boston 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 Garching, Germany  Cap

Scientific case:  +p capture  capture probes axial structure of nucleon  capture  decay hadronic vertex dressed by QCD  q 2 dependent form-factors dual role of   acts as well defined probe of hadronic structure QCD tests, pseudoscalar form-factor g P, chiral symmetry Standard Model symmetries of lepton-quark interaction p n e e-e- n  p -- W W  - + p   + n  Cap

Nucleon charged current at q 2 = m  2 J  = V  - A  V   g V (q 2 )   + ig M (q 2 )/2M   q  + g S (q 2 )/m q  A   g A (q 2 )     + g P (q 2 ) q  /m   + ig T (q 2 )/2M   q    Vector current in SM determined via CVC g V (0)=1, g(q 2 )=1+q 2 r 2 /6, r V 2 =0.59 fm 2 g M (0)=  p -  n -1= , r M 2 =0.80 fm 2 q 2 dependence from e scatt. Axial vector FF from experiment g A (0)=1.2670(35), r A 2 =0.42±0.04 fm 2 q 2 dependence from quasi-elastic scattering,  e-production 2 nd class FF g S, g T forbidden by G symmetry, e.g. g T /g A =-0.15 ±0.15 (exp), ±0.0053(QCD sum rule, up-down mass difference) error from  V ud = 0.16 % nucleon weak formfactors g V,g M,g A determined by SM symmetries and data contribute <0.4% uncertainty to  S g V = (5) g M = (25) g A = 1.245(3) remains g P = ?  Cap

pseudoscalar form factor g P PCAC: g P =8.7 heavy baryon chiral perturbation theory: g P =(8.74  0.23) – (0.48  0.02) = 8.26  0.23 g  NN 13.31(34) 13.0(1) 13.05(8)  calculations O(p 3 ) show good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO n  p --  g  NN FF *NLO result fundamental and least known weak nucleon FF solid theoretical prediction at 2-3% level basic test of QCD symmetries Recent reviews : T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/ , Jun 2002 V. 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% level basic test of QCD symmetries Recent reviews : T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/ , Jun 2002 V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1  Cap

Experimental information on g P O rdinary M uon C apture  - + p   + n R adiative M uon C apture  - + p   + n +  BR~10 -3, 8 experiments , BC, neutron, electron detection “in principle” most direct g P measurement BR~10 -8, TRIUMF (1998), E  >60 MeV, 297 ± 26 events closer to pion pole  3x sensitivity of OMC theory more involved (min substitution, ChPT) Muon capture in nuclei  + 3 He  + 3 H  st =1496 ±4 s -1 PSI (1998) g p =g p th (1.08 ±0.19) error dominated by 3-N theory correlation measurements Neutrino scattering  electro production at threshold  Cap

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 = )  SR effect for  + TT SS  pp  pp pp  ortho  para F=0 F=1 J=1 J=0 OP n+  Cap

Muon Capture and g P ChPT OP (ms -1 ) gPgP 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 4  discrepancy exp/th no overlap theory & OMC & RMC OMC not precise, ambiguous interpretation RMC 4  discrepancy exp/th no overlap theory & OMC & RMC  Cap

 Cap experimental strategy New idea: active target of ultra-pure H 2 gas 10 bar measure   + and   -   S = 1/   - - 1/   +,   to TPC ePC1  ePC2 eSC e  Cap

experimental strategy Physics Unambigous interpretation At low density (1% LH 2 ) 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 (c Z <10 -8, c d <10 -6 ) hydrogen chambers bakeable to 150 C, continuous purification TPC monitors capture on impurity and transfer to deuterium sensitivity with gas chromatograph  + SR: calibrated with tranverse field 70 G Statistics statistics: Complementary analysis methods pp  P pp  O pp pp pp pp  P pp  O time (  s) 100% LH 2 1 % LH 2 10% LH 2  Cap

time projection chamber electron detector  Cap detector  Cap

TPC tracking muon decay rare impurity capture  +Z  Z’+n+  Cap

-- ++  transfer to deuterium, diffusion  p+d   d + p Ramsauer Townsend minimum in  d + p scattering at 1.6 eV diffusion  catalyzed pd fusion  d + p  p  d   (5.3MeV)+ 3 He(0.2KeV)  Cap

Gas purification and analysis Hydrogen purification and analysis to better than Electrolytic generator purity ~0.3 ppm Pd filter cleaning from O 2 and N 2 to better directly verified. TPC gas purity deterioration can be reduced by longer conditioning after N 2 filling. Continuous purification system under construction. Different methods of D 2 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, 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 %, g P 2-3% 20-30x exp improvement  S similar precision as  n exp challenges: statistics, purity, atomic physics *P.K. et al, PSI letter of intent 1998  Cap

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 experiment g P 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 G F 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