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Unblinding the MuCap experiment the final results of μ p capture rate Λ S

Unblinding the MuCap experiment the final results of μ p 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/.

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Unblinding the MuCap experiment the final results of μ p capture rate Λ S

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  1. Unblinding the MuCap experiment the final results of μp capture rateΛS and of electro-weak coupling constant gP LTP Seminar April 23, 2012 Claude Petitjean PSI theor. & exp. gP 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 ΛS gP Petitjean LTP-Seminar 23.04.12

  3. MuCap proposal 1997 1% precision measurement of singlet nuclear muon capture rateΛs • semi-leptonicweak interaction process • determines the induced pseudoscalar coupling gPto6% • 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) Petitjean LTP-Seminar 23.04.12

  4. p n W νμ μ- 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: q2 dep. form-factors (gV,gM,gA,gP) μp-capture is the only process sensitive to the nucleon form factor gP μ- + p  νμ+ n (analogue) n p W e- νe prediction of heavy baryon chiral perturbation theory (V. Bernard et al. 1994): gPtheory=8.26  0.23 -gp 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 ΛS from gA & gP gA from neutron β decay ↓ ↓ ↓ ← - 1% ←ΛSth= (711.5 ± 4.6) s-1 (incl. rad. correction) ← + 1% a 1% Λs measurement determines gp to ~ 6% the QCD prediction (HBChPT) is ± 2-3% Petitjean LTP-Seminar 23.04.12

  6. experimental challenges of μ- in pure hydrogen solutions of MuCap experiment m → enn ΛCAPreduces lifetime by ~1.6x10-3 log(counts) λμ+ λμ- μ+ μ – te-tm • high precision measurement • of absolute capture rate • - high statistics (1010 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) lifetime method (likeSaclay)  ΛS = λ(μ-p) – λ(μ+) muon beam with kicker hydrogen TPC operated in low density H2gas  Φ ~ 0.01 (lq=1) use of UHV materials continuous gas circulation system (CHUPS)   cZ>1 ≤ 20 ppb HD separation column D-depletion cd < 7 ppb  Petitjean LTP-Seminar 23.04.12

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

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

  9. the Hydrogen TPC as active muon stop target developed 2001-03 at PSI all wires soldered on special glass frames pure metal & ceramic structure bakeable to 130 C filling 10 bar ultra-pure protium gas UHV = -30 kV MWPC with Ucath = -(5-6) kV Edrift = 2 kV/cm - vdrift = 0.55 cm/μs sensitive volume (12 x 15 x 30) cm3 Petitjean LTP-Seminar 23.04.12

  10. first MWPC module tested in 2001 details of the TPC 75 anode wires 35x4 cathode wires 2-D hor. readout + vert. drift time → 3-D reconstruction of μ tracks reliable operation achieved in 2004-07 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. strips anodes TPC performance shown in the event display TPC signals showing a clean muon stop event 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 λppμ) ** • ortho-para transitions (rate λop) • 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. impurities: removal with CHUPS • (Cont. H2Ultra-Purification System, developed in Gatchina) • - cryogenic adsorption/desorption cycles in active Carbon • - Zeolite in liquid nitrogen absorbs all Z>2 impurities: cN2<5ppb, cH2O ~17ppb CHUPS during main runs N2 gas chromatography H2O our main impurity source was water vapor from walls & materials humidity sensor Petitjean LTP-Seminar 23.04.12

  15. cleaning effect of CHUPS gas circulation calibration run with 11 ppm N2 calibration Petitjean LTP-Seminar 23.04.12 thesis B. Kiburg

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

  17. ΛT ~12s-1 n+n n+n triplet (F=1) pμ↑↑ ΛOM ~540s-1 μ- ppμ ppμ λop ortho (J=1) para (J=0) pμ↑↓ singlet (F=0) ΛS ~710s-1 n+n II. ppμ molecule formation – the ortho-para problem n+n ΛPM ~213s-1 τ~10ns φλppμ • - ppμ formation rate λppμwas known to ± 30% only • ortho  paratransitionλop known to ± 50% only • - capture ratesΛS - ΛOM - ΛPM very different - our observed capture rate is not pureΛS - at our gas density (10 bar) φ= 1.13% of lq H2 gives toΛSa 3% correction with large error bar - determine φλppμby a special Argon doped run – remeasureλopfrom n-time spectra (to be done!) problem: solution: Petitjean LTP-Seminar 23.04.12

  18. 1% lq. H2 100% lq. H2 pm ppmO pm ppmO ppmP ppmP → time (μs) development of atomic & molecular states of μ in H2 (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. experimental situation on gP before MuCap gP - + p  m+ n @ Saclay - + p  m+ n + g@TRIUMF HBChPT  (8.26) MuCap precisiongoal TRIUMF 2006 Saclay 1981 theory lop(ms-1) experiments & loprates are inconsistent  Saclay experiment (in lq. H2) cannot be interpreted! Petitjean LTP-Seminar 23.04.12

  20. new ppμ measurement using 18.5 ppm Argon admixture kinetics scheme with ratesΛppμ, ΛpAr,ΛAr 5x108 events Χ2/NDF = 0.98  Λppμ= ppμ 2.30x10-2s-1 ppμ μp ΛpAr= cArpAr 4.46 x10-2 s-1 μAr   new result measured at MuCap conditions: ppμ = 1.99 ± 0.058statμs-1 (prelim.) (thesis Sara Knaack, to be published) ΛAr1.3s-1 μ+ArCl+n+ correction to observed ΛS: ΔΛppμ = (18.2±2.5) s-1(2.5%) Petitjean LTP-Seminar 23.04.12

  21. 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! (a) μ enters TPC & ionizes gas (b) charge drifts towards MWPC (c) decay electron deposits energy (d) can generate or augment pixels thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

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

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

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

  25. lifetime fits vs. NCEH 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  thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

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

  27. World Record: cd < 6 ppb V. diffusion of μd: remove all deuterium by a H-D isotope separation column (developed by Gatchina & PSI 2006/07) principle: - H2 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 H2 at the bottom is slowly removed AMS protium analysis at ETHZ: in 2004: cd = (1.45±0.15)10-6 in 2006-07:cd < 6*10-9 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 ΔΛS = -3.0 ± 0.1 s-1 (0.4% of ΛS) thesis B. Kiburg Petitjean LTP-Seminar 23.04.12

  29. 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. μp lifetimes & evaluation ofcapture rate ΛS [s-1] Petitjean LTP-Seminar 23.04.12

  35. the induced pseudoscalar coupling constant gP δΛS/ΛS =-0.197δgP/gP  δgPMuCap = -0.021 gPChPT gPChPT = 8.26 ± 0.23 gPMuCap = 8.1 ± 0.5 (preliminairy!) excellent agreement with chiral perturbation theory!  Petitjean LTP-Seminar 23.04.12

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

  37. MuCap collaboration & authors of P.R. Lett. 99, 032002 (2007) 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 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), USA* *now University of Washington (UW), Seattle, USAUniversité Catholique de Louvain, BelgiumUniversity of Kentucky, Lexington, USABoston University, USA (graduate students in red) parts of the collaboration during the main run in 2006 at PSI Petitjean LTP-Seminar 23.04.12

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