Peter Kammel University of Illinois at Urbana-Champaign www.npl.uiuc.edu/exp/mucapture

1. MuCap Collaboration V.A. Andreev, T.I. Banks, B. Besymjannykh, L. Bonnet, R.M. Carey, T.A. Case, D. Chitwood, S.M. Clayton, K.M. Crowe, P. Debevec, J. Deutsch, P.U. Dick, A. Dijksman, J. Egger, D. Fahrni, O. Fedorchenko, A.A. Fetisov, S.J. Freedman, V.A. Ganzha, T. Gorringe, J. Govaerts, F.E. Gray, F.J. Hartmann, D.W. Hertzog, M. Hildebrandt, A. Hofer, V.I. Jatsoura, P. Kammel, B. Kiburg, S. Knaak, P. Kravtsov, A.G. Krivshich, B. Lauss, M. Levchenko, E.M. Maev, O.E. Maev, R. McNabb, L. Meier, D. Michotte, F. Mulhauser, C.J.G. Onderwater, C.S. Özben, C. Petitjean, G.E. Petrov, R. Prieels, S. Sadetsky, G.N. Schapkin, R. Schmidt, G.G. Semenchuk, M. Soroka, V. Tichenko, V. Trofimov, A. Vasilyev, A.A. Vorobyov, M. Vznuzdaev, D. Webber, P. Winter, P. Zolnierzcuk Petersburg Nuclear Physics Institute (PNPI), Gatchina, RussiaPaul Scherrer Institute (PSI), Villigen, Switzerland University of California, Berkeley (UCB and LBNL), USAUniversity of Illinois at Urbana-Champaign (UIUC), USAUniversité Catholique de Louvain, BelgiumTU München, Garching, GermanyUniversity of Kentucky, Lexington, USABoston University, USA First Physics Results from the MuCap Experiment at PSI • Contents • Physics Context • Muon Capture on the Proton Theory – Experiment • mCap and First Results Peter KammelUniversity of Illinois at Urbana-Champaignwww.npl.uiuc.edu/exp/mucapture Topics in Nuclear PhysicsDNP, October 28, 2006

2. u gm(1-g5) d W m n Nuclear Physics Context charged current • EW current key probe for nucleon structure • Understanding hadrons from fundamental QCD • lattice QCD • chiral effective field theory (ChPT) p Goldstone boson of spontaneously broken symmetry, sys. expansion in q/L model independent predictions fundamental properties and symmetry tests interesting processes (astrophysics) interface to lattice calculations… nucleon level quark level q q relevant degrees of freedom ? W m n

3. Muon Capture and Axial NucleonStructure • - + p  m+ n • rate LS + second class currentssuppressed by isospin symm. Lorentz, T invariance Conserved Vector Current CVC Vector form factorsq2= -0.88 mm2 gV = 0.9755(5) gM = 3.5821(25) strong program JLab, Mainz, ... Axial form factorsq2= -0.88 mm2 gA = 1.245(4) gP = 8.3 ± 50% Main motivation formCap studies

4. Axialvector Form Factor gA Lattice QCD Axial radius Exp. History n+N scattering consistent with p electroproduction (with ChPT correction) Bernard et al. (2002) Edwards et al. LHPC Coll (2006) PDG 2006 introduces 0.4% uncertainty to LS (theory)

5. gpNN n p p Fp m- nm Pseudoscalar Form Factor gP gP determined by chiral symmetry of QCD: gP= (8.74  0.23) – (0.48  0.02) = 8.26  0.23 PCAC pole term Adler, Dothan, Wolfenstein ChPT leading order one loop two-loop <1%N. Kaiser Phys. Rev. C67 (2003) 027002 Lincoln Wolfenstein, Ann. Rev. Nucl. Part. Sci. 2003 … The radiative muon capture in hydrogen was carried out only recently with the result that the derived gP was almost 50% too high. If this result is correct, it would be a sign of new physics that might contribute effectively to V, A or P. • gP basic and experimentally least known weak nucleon form factor • solid QCD prediction via ChPT (2-3% level) • basic test of QCD symmetries Recent reviews:T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1

6. 1% LS Calculations

7. Processes to Determine gP • - + p  m+ n OMC rate LSBR~10-3 • 8 experiments, typical precision 10-15%, Saclay 4% • - + p  m+ n + g RMCBR~10-8, E>60 MeV • - + 3He  m+ 3H • pion electroproduction 279±25 eventsBRg(k>60MeV)=(2.10±0.21)x10-8 Wright et al. (1998) … rad. corrections?

8. 1 % LH2 100% LH2 pm ppμ ppmO • Interpretation requires knowledge of ppm population • Strong dependence on hydrogen density f ppμ pm rate proportional to H2 density f ! ppmO ppmP ppmP time (ms) Muon capture and muon molecular processes LT = 12 s-1 triplet (F=1) pμ↑↑ Lortho=506s-1 Lpara=200s-1 λop μ ppμ ppμ f λppm ortho (J=1) para (J=0) pμ↑↓ singlet (F=0) LS= 691s-1 n+n

9. Precise Theory vs. Controversial Experiments gP - + p  m+ n @ Saclay - + p  m+ n + g@TRIUMF ChPT mCapprecisiongoal TRIUMF 2005 exp theory lOP(ms-1) • no overlap theory & OMC & RMC • large uncertainty in lOP gP  50% ?

10. mCap Experimental Strategy • Lifetime method • 1010m→enn decays • measure - to 10ppm, • S = 1/- - 1/+to 1% • Unambiguous interpretation • capture mostly from F=0 mp state at 1% LH2 density • Clean m stop definition in active target (TPC) • to avoid:mZ capture, 10 ppm level • Ultra-pure gas system and purity monitoring • to avoid: mp + Z mZ+ p, ~10 ppb impurities • Isotopically pure “protium” • to avoid: mp + d md+ p, ~1 ppm deuterium • diffusion range ~cm fulfill all requirements simultaneouslyunique mCap capabilities

11. mCap Detector Design 2001-2 Reality 2004 e m

12. m- Muon Stops in Active Target 10 bar ultra-pure hydrogen, 1.16% LH2 2.0 kV/cm drift field ~5.4 kV on 3.5 mm anode half gap bakeable glass/ceramic materials Operation with pure H2 challenging, R&D @ PNPI, PSI Observed muon stopping distribution E p e- 3D tracking w/o material in fiducial volume

13. Time Spectra m- m-e impact parameter cut huge background suppression diffusion (deuterium) monitoring m+as reference identical detector systematics different physics m+ mSRin 50G blinded master clock frequency

14. 6 mm Inside TPC Consistency Studies TPC fiducial cuts Start time fit Event selection cuts

15. Results cN, cO < 7 ppb, cH2O~30 ppb correction based on observed capture yield x t z Imp. Capture mCap Unique Capabilities: Impurities • rare impurity capture mZ(Z-1)+n+n • LZ (C, N, O) ~ (40-100) x LS • ~10 ppb purity required • Hardware • CirculatingHydrogenUltrahighPurificationSystem • Gas chromatography • CRDF 2002, 2005 • Diagnostic in TPC

16. Results Directly from data cd= 1.49 ± 0.12 ppm AMS (2006) cd= 1.44 ± 0.15 ppm On-site isotopic purifier 2006 (PNPI, CRDF) mCap Unique Capabilities: mp, md diffusion • mp + d  md + p (134 eV) • large diffusion range of md • < 1 ppm isotopic purity required m-e impact par cut mp md mp e- e- or to wall • Diagnostic: • l vs. m-e vertex cut • AMS, ETH Zurich World Record cd < 0.1 ppm

17. Beamline Kicker Plates m detector m- TPC +12.5 kV -12.5 kV 50 ns switching time mCap Unique Capabilities: Muon-On-Demand • Single muon requirement (to prevent systematics from pile-up) • limits accepted m rate to ~ 7 kHz, • while PSI beam can provide ~ 70 kHz • Muon-On-Demand concept • Muon-On-Demand concept mLan kickerTRIUMF rf design 2-Dec-2005 kicked Fig will be improved dc ~3 times higher rate

18. Corrections & preliminary results data 2004 Unblinding

19. mCap and LS calculations preliminary • rad. corrections • Goldman (1972) • Czarnecki Marciano Sirlin (2006)private comm.preliminary MuCap agrees within ~1s with LS theory Thorough theory studies needed for next MuCap 1% stage !

20. mCap and gP preliminary • within one sigma of chiral prediction, no dramatic discrepancy • nearly independent of molecular physics (lOP) • has overlap with old OMC, barely with recent RMC result • final result (’06 and ’07 data) will reduce error to 7%

21. Summary and Plans • Preliminary results 2004 data preliminary mCap theory*LS 730 18 707 - 715 gP 6.95  1.09 8.26 0.23 • 2006 data and 2007 plans • 1010 events m- achieved in 2006 • 1010 events m+ and suppl. measurements in 2007 LS with 1% uncertainty • m+d proposal planned for 2007 • Ideas for ultrapure H2 TPC welcome *including Czarnecki et al. rad. corrections