1. Unblinding the MuCap experiment the final results of μp capture rate Λ S and of electro-weak coupling constant g P LTP Seminar April 23, 2012 Claude Petitjean PSI theor. & exp. g P bands vs. Ortho-Para transition rate MuCap homepage http://muon.npl.washington.edu/exp/MuCap/ Petitjean LTP-Seminar 23.04.12

2. outline - goal of MuCap experiment, theory - experimental challenges  MuCap apparatus with TPC - systematics: - impurities - formation of ppμ molecules  Argon doped run - interferences with electron charges - μp scattering & diffusion  list of systematic corrections - unblinding of main runs 2006/07 - new results on Λ S  g P Petitjean LTP-Seminar 23.04.12

3. 1% precision measurement of singlet nuclear muon capture rate Λ s - semi-leptonic weak interaction process - determines the induced pseudoscalar coupling g P to 6% - constitutes a vigorous test of low energy HBChPT thesis works by T.I. Banks (UC Berkeley), S.M. Clayton (UI Urbana Campaign), B.E. Kiburg, S. Knaak (both UIUC, now UW Seattle) MuCap proposal 1997 Petitjean LTP-Seminar 23.04.12

4. scientific case of μ capture on the proton μ capture probes axial structure of nucleon μ capture neutron β decay hadronic vertex determined by QCD: q 2 dep. form-factors (g V,g M,g A,g P ) μp-capture is the only process sensitive to the nucleon form factor g P pn νeνe e-e- n νμνμ p μ-μ- W W μ - + p  ν μ + n (analogue) prediction of heavy baryon chiral perturbation theory (V. Bernard et al. 1994): g P theory = 8.26  0.23 - g p least known of the nucleons weak form factors - solid QCD prediction by HBChPT at the 2-3% level (NNLO < 1%) - basic test of chiral symmetries and low energy QCD - V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1 - T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31 - P. Kammel, K. Kubodera, Annu. Rev. Nucl. Part. Sci. 60 (2010) 327 recent reviews: Petitjean LTP-Seminar 23.04.12

5. dependence of Λ S from g A & g P g A from neutron β decay ↓ ↓ ↓ ← - 1% ← Λ S th = (711.5 ± 4.6) s -1 (incl. rad. correction) ← + 1% a 1% Λ s measurement determines g p to ~ 6% the QCD prediction (HBChPT) is ± 2-3% Petitjean LTP-Seminar 23.04.12

6. experimental challenges of μ - in pure hydrogen - high precision measurement of absolute capture rate - high statistics (  10 10 events) - all μ must stop in hydrogen (no wall stops!) + avoid formation of ppμ molecules (Ortho-Para problem) - ultra-high gas purity avoid μp → μZ transfers to impurities - ultra-high isotopic purity avoid μp → μd transfers (diffusion problem) solutions of MuCap experiment lifetime method (likeSaclay)  Λ S = λ (μ - p) – λ (μ + ) muon beam with kicker hydrogen TPC operated in low density H 2 gas  Φ ~ 0.01 (lq=1) use of UHV materials continuous gas circulation system (CHUPS)   c Z>1 ≤ 20 ppb HD separation column D-depletion c d < 7 ppb  log(counts) t e -t  μ+μ+ μ – λμ+λμ+ λμ- λμ- Λ CAP reduces lifetime by ~1.6x10 -3  → e Petitjean LTP-Seminar 23.04.12

7.  e cut out view of MuCap detector used in 2003-07 Petitjean LTP-Seminar 23.04.12

8. the MuCap detector with rolled back TPC Petitjean LTP-Seminar 23.04.12

9. MWPC with U cath = -(5-6) kV E drift = 2 kV/cm - v drift = 0.55 cm/μs sensitive volume (12 x 15 x 30) cm 3 all wires soldered on special glass frames pure metal & ceramic structure bakeable to 130 C the Hydrogen TPC as active muon stop target developed 2001-03 at PSI filling 10 bar ultra-pure protium gas U HV = -30 kV Petitjean LTP-Seminar 23.04.12

10. details of the TPC 75 anode wires 35 x 4 cathode wires 2-D hor. readout + vert. drift time → 3-D reconstruction of μ tracks reliable operation achieved in 2004-07 first MWPC module tested in 2001 mounting the final TPC in 2003 details of wiring Petitjean LTP-Seminar 23.04.12

11. first TPC assembly by PSI engineers in 2002 Petitjean LTP-Seminar 23.04.12

12. TPC performance shown in the event display anodes strips TPC signals showing a clean muon stopevent with nuclear recoil from Z>1 capture allows monitoring of impurities Petitjean LTP-Seminar 23.04.12

13. precision lifetime measurement is understanding the systematics! the major issues in MuCap: I impurities calibration with doped gas mixtures * II formation of ppμ molecules (rate λ ppμ ) ** ortho-para transitions (rate λ op ) III electron interference with muon tracks * IV μ + p scatters * V diffusion of μd VI diffusion of μp * * thesis Brendan Kyburg ** thesis Sara Knaack Petitjean LTP-Seminar 23.04.12

14. I.impurities: removal with CHUPS (Cont. H 2 Ultra-Purification System, developed in Gatchina) - cryogenic adsorption/desorption cycles in active Carbon - Zeolite in liquid nitrogen absorbs all Z>2 impurities: c N 2 <5ppb, c H 2 O ~17ppb CHUPS during main runs our main impurity source was water vapor from walls & materials H2OH2O N2N2 gas chromatography humidity sensor Petitjean LTP-Seminar 23.04.12

15. cleaning effect of CHUPS gas circulation thesis B. Kiburg calibrationcalibration calibration run with 11 ppm N 2 Petitjean LTP-Seminar 23.04.12

16. effect on μ lifetime determined with extrapolation method ppm impurity admixtures  correction to Λ S : -7.8 ± 1.87 (2006); -4.54 ± 0.93 (2007) [s -1 ] (-1.1%) (-0.6%) thesis B. Kiburg syst. error due to badly known ratio α = Y N /Y all we include: 0<α<1 Petitjean LTP-Seminar 23.04.12

17. Λ PM ~213s -1 Λ T ~12s -1 pμ ↑↓ singlet (F=0) Λ S ~710s -1 n+ triplet (F=1) μ-μ- pμ ↑↑ n+ ppμ para (J=0)ortho (J=1) Λ OM ~540s -1 λ op n+ φλ ppμ n+ - ppμ formation rate λ ppμ was known to ± 30% only - ortho  para transition λ op known to ± 50% only - capture rates Λ S - Λ OM - Λ PM very different τ~10ns - our observed capture rate is not pure Λ S - at our gas density (10 bar) φ = 1.13% of lq H 2 gives to Λ S a 3% correction with large error bar - determine φ λ ppμ by a special Argon doped run – remeasure λ op from n-time spectra (to be done!) II. ppμ molecule formation – the ortho-para problem problem: solution: Petitjean LTP-Seminar 23.04.12

18. pp  P pp  O pp 100% lq. H 2 pp pp  P pp  O 1% lq. H 2 → time (μs) development of atomic & molecular states of μ in H 2 (a) liquid hydrogen, φ = 1 (b) hydrogen gas at φ = 0.01 pμ depopulated in 1-2 μs pμ remains dominant ~ 81% ppμ formation ~ 5% ppμ formation badly known ortho-para ratio! small effects from o  p transitions! Petitjean LTP-Seminar 23.04.12

19. op (ms -1 )  - + p   + n +  @ TRIUMF MuCap precision goal Saclay 1981theory TRIUMF 2006  - + p   + n @ Saclay experimental situation on g P before MuCap experiments & op rates are inconsistent  Saclay experiment (in lq. H 2 ) cannot be interpreted! gPgP HBChPT  (8.26) Petitjean LTP-Seminar 23.04.12

20. new ppμ measurement using 18.5 ppm Argon admixture μpμp ppμ Λ ppμ =  ppμ 2.30x10 -2  s -1   Λ pAr =  c Ar pAr 4.46 x10 -2  s -1 μAr μ +Ar  Cl+n+  Λ Ar  1.3  s -1 kinetics scheme with rates Λ pp μ, Λ pAr, Λ Ar new result measured at MuCap conditions: ppμ = 1.99 ± 0.058 stat μs -1 (prelim.) (thesis Sara Knaack, to be published) correction to observed Λ S : ΔΛ ppμ = (18.2±2.5) s -1 (2.5%) 5x10 8 events Χ 2 /NDF = 0.98 Petitjean LTP-Seminar 23.04.12

21. (c) decay electron deposits energy (d) can generate or augment pixels (a) μ enters TPC & ionizes gas (b) charge drifts towards MWPC III. electron interference with muon tracks: charge deposition from decay electrons can generate or modify pixels of a muon track  acceptance of events may become time dependent! thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

22. EL Pixel separated from track added near the track EH Pixel EL pixel “upgraded” this modifies NC EH in a complicated way example of an interference between a muon track and the decay electron producing blue pixels crucial parameter is NC EH (# of EH pixels) thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

23. μ + p scatters generates EH pixel on one anode  cut NC EH = 1 events IV.μ + p scatters: can fake a μ stop, but actually stops in surrounding high Z material & distorts the lifetime thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

24. fast neutron time component in NC EH =1 events due to μ + p scatters leaving the TPC thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

25. thesis B. Kiburg lifetime fits vs. NC EH upper e-detector: no μ-e interference, but effect from μ-e scatters  lower e-detector: μ-e interference with μ track is time and space dependent  Petitjean LTP-Seminar 23.04.12

26. match NC EH =2 + determine NC EH =1 distortion allows μ + p scatter estimate correction of μ + p scatter effects: the μ + data has NC EH interference, but no μ + p scatter distortion in NC EH = 1 thesis B. Kiburg correction to Λ S : -12.4 ± 3.2 (2006); -7.20 ± 1.25 (2007) [s -1 ] (-1.7%) (-1.0%) Petitjean LTP-Seminar 23.04.12

27. V. diffusion of μd: remove all deuterium by a H-D isotope separation column ( developed by Gatchina & PSI 2006/07) principle: - H 2 gas circulates from bottom to cold head at top & gets liquefied - liquid droplets fall down & evaporize  gas phase gets depleted from D - the D-enriched liquid H 2 at the bottom is slowly removed AMS protium analysis at ETHZ: in 2004: c d = (1.45±0.15)10 -6 in 2006-07: c d < 6 * 10 -9 World Record: c d < 6 ppb Petitjean LTP-Seminar 23.04.12

28. VI. μp diffusion: it distorts the lifetime slope! impact parameter  our choice of impact parameter is 120 mm resulting in a correction due to μp diffusion of ΔΛ S = -3.0 ± 0.1 s -1 (0.4% of Λ S ) thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

29. sourceold run8 (2004) Phys. Rev. Lett. 99, 032002 (2007) new run10 (2006) P. Winter et al. new run11 (2007) B. Kiburg et al. remarks units -1 μ+p scatter 0 ± 3.0-12.40 ± 3.22*-7.20 ± 1.25*err. prelim. μ+p diffusion -2.7 ± 0.5-3.1 ± 0.1-3.0 ± 0.1 μ+d diffusion -10.2 ± 1.6 0 0cd < 7 ppb High-Z impurities -19.2 ± 5.0-7.80 ± 1.87-4.54 ± 0.93 entrance counter inefficiencies 0 ± 3.0 0 ± 0.5 e det. - definition 0 ± 5.0 0 ± 1.8* err. prelim. fiducial volume cut - 0 ± 3.0 total correction-32.1 ± 8.5-23.3 ± 5.1*-14.7 ± 3.9**error correlated systematic corrections to μ and errors [s -1 ] Petitjean LTP-Seminar 23.04.12

30. lifetime fit of full run11 statistics thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

31. MuCap‘s new physics results from unblinding the 2006 & 2007 data at UW Seattle, Dec 16, 2011 (preliminary) Petitjean LTP-Seminar 23.04.12

32. lifetime fit results in blinded mode (with unknown offset of master clock) Petitjean LTP-Seminar 23.04.12

33. final lifetime results after unblinding Dec 16, 2011 Petitjean LTP-Seminar 23.04.12

34. old run8 (2004) Phys. Rev. Lett. 99, 032002 (2007) new run10 (2006) evaluated by P. Winter et al. new run11 (2007) evaluated by B. Kiburg et al. remarks statistics1.6 x 10 9 5.5 x 10 9 5.0 x 10 9 events after cuts μ- fit 455‘883.5 ± 12.5455‘880.4 ± 7.0455‘867.0 ± 7.6  2 /NDF ~1.15±0.1 syst. corr. -32.1 ± 8.5 -23.3 ± 5.1 -14.7 ± 3.9systematical error μ- corr. 455‘851.4 ± 12.5455‘857.1 ± 7.7455‘852.3 ± 8.3stat. error inflated μ - average all runs 455‘854.2 ± 7.2 stat.+sys. errors combined μ+ 455‘170.2 ± 0.5 Phys. Rev. Lett. 106, 041803 (2011) final MuLan result Δ μp +12.3 Phys. Rev. 119(1), 365 (1960) bound state effect ΔΛ pμp +18.2 ± 2.5 pμp formation ΛSΛS = μ- - μ+ + Δ μp + ΔΛ pμp 714.5 ± 7.6 (±5.4 stat ±5.4 sys ) preliminary (within < 0.5s -1 ) final MuCap result ΛSΛS 711.5 ± 4.6 theory μp lifetimes & evaluation of capture rate Λ S [s -1 ] Petitjean LTP-Seminar 23.04.12

35. the induced pseudoscalar coupling constant g P δ Λ S /Λ S = -0.197 δ g P /g P  δ g P MuCap = -0.021 g P ChPT g P ChPT = 8.26 ± 0.23 g P MuCap = 8.1 ± 0.5 (preliminairy!) excellent agreement with chiral perturbation theory!  Petitjean LTP-Seminar 23.04.12

36. g P (MuCap prelim.) = 8.1 ± 0.5 g P (theory) = 8.26 ± 0.23 precise & unambiguous MuCap result solves longstanding puzzle Petitjean LTP-Seminar 23.04.12

37. V.A. Andreev, T.I. Banks, T.A. Case, D. Chitwood, S.M. Clayton, K.M. Crowe, J. Deutsch, J. Egger, S.J. Freedman, V.A. Ganzha, T. Gorringe, F.E. Gray, D.W. Hertzog, M. Hildebrandt, P. Kammel, B.E. Kiburg, S. Knaak, P. Kravtsov, A.G. Krivshich, B. Lauss, K.L. Lynch, E.M. Maev, O.E. Maev, F. Mulhauser, C.S. Özben, C. Petitjean, G.E. Petrov, R. Prieels, G.N. Schapkin, G.G. Semenchuk, M. Soroka, V. Tichenko, A. Vasilyev, A.A. Vorobyov, M. Vznuzdaev, P. Winter MuCap collaboration & authors of P.R. Lett. 99, 032002 (2007) Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia Paul Scherrer Institute (PSI), Villigen, Switzerland University of California, Berkeley (UCB and LBNL), USA University of Illinois at Urbana-Champaign (UIUC), USA* *now University of Washington (UW), Seattle, USA Université Catholique de Louvain, Belgium University of Kentucky, Lexington, USA Boston University, USA parts of the collaboration during the main run in 2006 at PSI (graduate students in red) Petitjean LTP-Seminar 23.04.12