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Precision Measurement of Muon Capture on the Proton “ m Cap experiment”

Precision Measurement of Muon Capture on the Proton “ m Cap experiment”.  - + p   m + n. www.npl.uiuc.edu/exp/mucapture/.

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Precision Measurement of Muon Capture on the Proton “ m Cap experiment”

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  1. Precision Measurement of Muon Capture on the Proton“mCap experiment” - + p  m+ n www.npl.uiuc.edu/exp/mucapture/ 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. mCap @ PSI

  2. 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 188350, RussiaP.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, SwitzerlandT.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. PrieelsUniversité 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-85747 Garching, Germany mCap

  3. p n W nm m- Scientific case: m+p capture • m capture probes axial structure of nucleon • m capture b decay • hadronic vertex dressed by QCD q2 dependent form-factors • dual role of m • m acts as well defined probe of hadronic structure QCD tests, pseudoscalar form-factor gP,chiral symmetry • Standard Model symmetries of lepton-quark interaction - + p  m+ n p n W e- ne mCap

  4. Nucleon charged current at q2= - 0.88 mm2 Ja = Va- Aa Va= gV(q2) ga + igM(q2)/2M sab qb + gS(q2)/m qa Aa= gA(q2) gag5 + gP(q2) qa/m g5+ igT(q2)/2M sab qbg5 • nucleon weak formfactors gV,gM,gA • determined by SM symmetries and data • contribute <0.4% uncertainty to LS • gV = 0.9755(5) • gM = 3.5821(25) • gA = 1.245(3) • remains • gP = ? • Vector current in SM determined via CVCgV(0)=1, g(q2)=1+q2 r2/6, rV2=0.59 fm2 gM(0)=mp-mn-1=3.70589, rM2=0.80 fm2 q2 dependence from e scatt. • Axial vector FF from experimentgA(0)=1.2670(35), rA2=0.42±0.04 fm2 q2 dependence from quasi-elastic n scattering, p 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 % mCap

  5. pseudoscalar form factor gP PCAC:gP=8.7 gpNN n p p Fp heavy baryon chiral perturbation theory: m- nm gP=(8.74  0.23) – (0.48  0.02) = 8.26  0.23 gpNN 13.31(34) 13.0(1)13.05(8) L calculations O(p3) show good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO 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 *NLO result mCap

  6. Experimental information on gP Ordinary Muon Capture- + p  m+ n BR~10-3, 8 experiments 1962-82, BC, neutron, electron detection “in principle” most direct gP measurement Radiative Muon Capture- + p  m+ n + g BR~10-8, TRIUMF (1998), Eg>60 MeV, 297 ± 26 eventscloser to pion pole 3x sensitivity of OMC theory more involved(min substitution, ChPT) • Muon capture in nuclei • m + 3He  n + 3HLst=1496 ±4 s-1 PSI (1998) gp=gpth (1.08 ±0.19) error dominated by 3-N theorycorrelation measurements • Neutrino scattering • p electro production at threshold mCap

  7. experimental challenges - p ()  m+ n m- e+ne+m p • (Rich) physics effects • Interpretation: where does capture occur ? • Critical because of strong spin dependence of V-A interaction m LS LT pm pm n+n F=0 F=1 Lortho • Background:Wall stops and diffusionTransfer to impurities mp+Z mZ+p • Rate and statistics (BR = 10-3) • mSR effect for m+ ppm n+n J=1 lOP Lpara ppm n+n J=0 mCap

  8. Muon Capture and gP gP update from Gorringe & Fearing RMC ChPT mCapproposed OMC Saclay exp theory lOP (ms-1) • OMC not precise, ambiguous interpretation • RMC 4s discrepancy exp/th • no overlap theory & OMC & RMC Interpretation of observed rate sensitive to ppm state, where capture occurs, atomic physics mCap

  9. mCap experimental strategy New idea: active targetof ultra-pure H2 gas 10 bar measure t+ and t-S = 1/- - 1/+ , tm to 10-5 ePC2 ePC1 TPC m e eSC mCap

  10. experimental strategy • Physics • Unambigous interpretationAt low density (1% LH2) mostly capture from mp(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 • m+SR: calibrated with tranverse field 70 G 100% LH2 10% LH2 1 % LH2 pm pm ppmO ppmO pm ppmO ppmP ppmP ppmP time (ms) • Statistics • 1010 statistics: Complementary analysis methods mCap

  11. time projection chamber mCap detector electron detector mCap

  12. TPC tracking muon decay rare impurity capture m+Z  Z’+n+n mCap

  13. m transfer to deuterium, diffusion Ramsauer Townsend minimum in md+ pscattering at 1.6 eV mp+d  md + p diffusion m+ m- m catalyzed pd fusion md+ p  pmd  m(5.3MeV)+3He(0.2KeV) mCap

  14. 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. mCap

  15. mCap status and plans • Planned schedule mCap 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 (LS 3%, 1%) • mCap II with muon-on-request beam* (2004, 2005)chopper development and m+ result from mLan • goal LS to 0.3 %, gP 2-3% • 20-30x exp improvementLS similar precision as tnexp challenges: statistics, purity, atomic physics mCap *P.K. et al, PSI letter of intent 1998

  16. Scientific Context Nucleon form factors, chiral symmetry of QCD m Cap experimentgP to < 7% (3% with mLan kicker) muon capture on proton- + p  m+ n L to 1 % Basic EW two nucleon reaction, calibrate v-d reactions mD project muon capture on deuteron- + d  m+ n +n L to 1 % Fermi Coupling Constant m Lan, FAST experiment GF to < 1ppm muon decay+  e++ne+m t+ to 1 ppm mCap

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