1. MuCap High-Precision Measurement of Muon Capture on the Proton BVR35 Progress report presented by Claude Petitjean, PSI 12 Febuary 2004 http://www.npl.uiuc.edu/exp/mucapture/ m

2. MuCap Experiment experimental goal principle of measurement apparatus time projection chamber (TPC) data from run in fall 2003 some results milestones reached in 2003 upgrades for run in fall 2004 Beam request 2004

3. MuCap 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, 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. Hildebrandt, 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, F.E. Gray, B. Lauss University of California Berkeley, UCB and LBNL, Berkeley, CA 94720, USA K.D. Chitwood, S.M. Clayton, P.T. Debevec, D. W. Hertzog, P. Kammel, B. Kiburg, R. McNabb, F. Mulhauser, C. J. G. Onderwater, C. Ozben, C.C. Polly, A. Sharp, D. Webber 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-85747 Garching, Germany  Cap

4. Experimental goal measure the rate Λ s of muon capture on the proton to 1% precision. Muon capture is a semileptonic weak interaction process, and occurs predominantly from the hyperfine singlet atomic bound state. a 1% measurement of Λ s determines g p – the “weak nucleonic charged current induced pseudoscalar form factor” – to < 7% precision. The QCD prediction (Heavy Baryon Chiral Pert. Theory) is ~2% precise.

5. problem of previous experiments TT SS  pp  pp pp  ortho  para F=0 F=1 J=1 J=0 OP n+ interpretation of rate  S due to formation of ppμ molecules in lq hydrogen and badly known rate OP of ortho-para transitions

6. Muon Capture and g P ChPT  OP (ms -1 ) gPgP RMC  Cap proposed Saclay exp theory OMC Saclay update from Gorringe & Fearing interpretation of g P vs OP ---------o--------- New TRIUMF exp

7. Experimental Technique “Lifetime” Method For μ –, muon capture competes with muon decay: This rate decreases the observed μ – lifetime from the vacuum lifetime, which we measure separately with μ + : Thus we need 10 ppm measurements of the μ+/- lifetimes or a statistics of at least 10 10 for both μ-decays

8. Experimental Technique “Lifetime” or “Disappearance” Method Since our experiment can only observe e + and e – decay products, muon capture produces a small downward deflection of the μ – lifetime curve from the μ + “vacuum” lifetime curve : The capture rate is easily calculated from the measured lifetimes: log(counts) time μ+μ+ μ –

9. Technical tasks of MuCap experiment ultra-clean 10-bar hydrogen gas target 0.01 ppm Z>1 impurities deuterium depleted hydrogen („protium“) < 1 ppm deuterium 100% stop identification no wall stops  TPC clean electron identification & tracking 2 cylindrical wire chambers unique μ  e decay assignment μ-stop – e-vertex matching high data rate 30 kHz μ stops high statistics > 10 10 events for μ + and μ - μSR under control for μ + 50-100 Gauss magnetic field tasks goals to be reached

10. Experimental Setup – Apparatus μ SC μ PC1 μ PC2 TPC ePC2 ePC1 eSC (Hodoscope) μ beam Muon Detectors Electron Detectors e-detectors cover 75% of 4π

11. assembly/tests: March-Aug 2003 data-taking: Sept-Oct 2003

12. U cathodes = 5-6 kV E = 2 kV/cm - v drift = 0.5 cm/μs sensitive volume (12 x 15 x 30) cm 3 TPC design drawing with glass frames and ceramic structure bakeable to 130 C

15. Online display of μ beam, μ stops in TPC and e in ePC1 ePC1/eSC(phi,z)

16. event display of muon stops & electrons

17. event display of μ stop + impurity capture

18. development of impurities during the 2 good data weeks full scale 1 ppm

20. summed decay time spectra showing pile-up suppression

21. μ – decay time spectra of 1 week with clean protium filling

22. MuCap 2003: exponential fits to each eSC counter pair

23. MuCap 2003: μSR enhanced fit of μ + decay time spectra

24. milestones 2003 protium production with < 0.5 ppm deuterium ultra-clean protium gas filling (< 0.1 ppm impurities) – after installation of a new Palladium filter new TPC@4.8 kV stable operation (perfect μ stop detector!) full e detector consisting of ePC1 and eSC new frontend electronics for ePC1 new compressor electronics for deadtime free ePC1 data collection new DAQ running with 4 MB/s data rate (80% duty cycle) new μSR magnet with ~50 Gauss field new slow control system full electronics for TPC, wire chambers and plastic counters collimated muon beam injection system analysis software in mature development

25. upgrades for 2004 protium: maintain 1 impurities new gas circulation, cleaning & diagnostics (Gatchina) e-detector: include new ePC2 (  vertex tracking) tune TPC to 5.5 kV (  online control of μd diffusion) new 0.5 mm Beryllium window (  increase good μ stops x 2) μ-detectors: new outside μPC1&2 (  reduce μ-absorption/range-tails) μ-beam: new tune in πE3 area (  < 3% momentum spread) new spare TPC from Gatchina (  >6 kV to see e tracks) upgrade DAQ for larger data flow (  ~100% duty cycle) upgrade μSR magnet with Alu coils (  reduce scattering of e) new online data analysis goal for 2004 : collect a significant part of 10 10 pileup-protected good μ-decays for μ + and μ -

28. protium gas circulation and purifying system (Gatchina)

29. MCstudy of μ stop distributions for various beam windows

30. MuCap experiment: time plans of upgrades for 2004 run

32. MuCap experiment: beam request for 2004 In 2004 we hope to approach closely the goal formulated in the proposal: a measurement of the μp singlet capture rate to ± 1% accuracy To accomplish this goal, we need area πE3 for the following activities: -setup of beamline with el.stat. separator, assemble full apparatus and electronics, test all components in the beam: 2 weeks -tune new 35 MeV/c muon beam: 1 week -test & optimize complete detector with beam: 1 week -data production towards 10 10 good μ - & μ + decays: 2 x 2.5 weeks -contingency for beam losses or other failures 1 week  we request 10 weeks in area πE3 (preferably in Oct-Dec 2004, at the end of the 2004 production cycle)