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Muon Capture in Hydrogen and Deuterium

Muon Capture in Hydrogen and Deuterium. EXA08 int. conference on exotic atoms & related topics Vienna Sept 15-18 2008 presentation by Claude Petitjean representing the MuCap- & the MuSun collaboration. g P vs. λ op plot showing first MuCap result.

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Muon Capture in Hydrogen and Deuterium

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  1. Muon Capture in Hydrogen and Deuterium EXA08 int. conference on exotic atoms & related topics Vienna Sept 15-18 2008 presentation by Claude Petitjean representing the MuCap- & the MuSun collaboration gP vs. λop plot showing first MuCap result collaboration homepages http://www.npl.uiuc.edu/exp/mucapture http://www.npl.uiuc.edu/exp/musun

  2. outline • experimental goals • comments to theories ChPT  gP - EFT  L1A • experimental challenges & strategy • - μ- kinetics in hydrogen - the ortho-para problem • MuCap apparatus, components • data & 1st results, final analysis • MuSun experiment: the new challenges • μd-kinetics • new Cryo-TPC • outlook

  3. Muon Capture Experiments in Hydrogen & Deuterium our goal precision measurement of muon capture rates to ±1% 1) μ- + p →(μ-p)↑↓→n + νμ singlet capture rate ΛS sensitive to induced pseudoscalar coupling gP in weak interactions first results published – full analysis in progress 2) μ- + d →(μ-d)↑↓→n + n + νμdoublet capture rate ΛD sensitive to the axial two-body current term L1A in effective field theories (EFT‘s) in full preparation – first run in Nov 2008

  4. p n W νμ μ- scientific case of μ capture on the proton μ capture probes axial structure of nucleon μ captureneutronβ 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) p n W e- νe heavy baryon chiral perturbation theory (Bernard et al. 1994): gPtheory=8.26  0.23 - gp least known of the nucleons weak form factors - solid theoretical prediction by HBChPT at 2-3% level - basic test of QCD symmetries

  5. scientific case ofμ capture on the deuteron μ + d  n + n + νμ model-independent connection via EFT & L1A • impact on fundamental astrophysics processes (SNO, pp) basic solar fusion reaction p + p  d + e+ +  •  key reactions for SNO  + d  p + p + e- (CC) •  + d  p + n +  (NC) • comparison of modern high precision calculations • (eff. field theories,standard nucl. physics approach) • EFT: axial current reactions related by single parameter L1A • the muon capture rate on deuteron determines L1A MECEFT L1A

  6. experimental challenges & our strategy (I) m → enn LSreduces lifetime by 10-3 λ+ log(counts) λ- μ+ μ – te-tm • only n & ν in output channel •  limited precision for direct • measurement of absolute rates •  use lifetime method • ΛS = λ(μ-p) – λ(μ+) • measure λ‘s to 10 ppm • >~ 1010 events required • capture rate small ~ 10-3 of λ(μ+) •  avoid any wall stops to 10-5! •  develop ultra-clean TPC • as active muon stop target • operated in hydrogen gas

  7. experimental challenges & our strategy (II) • μ-transfer to impuries (N2,H2O,..) • μp + N (O,..) →μN (μO,..) + p •  distortion of lifetime curves • develop continuously circulating • & cleaning system (CHUPS) • goal: cZ ~ 10-8 (10 ppb) • μ-transfer to deuterium • μp + d →μd + p • & large diffusion of μd atoms •  distortion of lifetime curves • develop new special • isotope separation column • goal: cd < 10-7 (100 ppb)

  8. ΛT ~ 12s-1 n+n n+n triplet (F=1) ΛOM ~540s-1 pμ↑↑ ppμ ppμ μ- λOP ortho (J=1) para (J=0) pμ↑↓ singlet (F=0) ΛS~710s-1 n+n experimental challenges & our strategy (III) kinetics of μ- in H2 n+n ΛPM ~213s-1 τ~10ns Λppμ • pμ↑↑ depopulates quickly (<100ns) • ppμmolecule formation with (τ~ 0.4μs/φ) • Λppμ known only to ± 20% • ortho to paratransition rate badly known • λOP known only to ± 50% • ΛS - ΛOM - ΛPM are all quite different! solution:- use low gas density φ(10 bar H2) ≈ 1% of liquid - determine Λppμby Argon doped run – λOP from neutron spectra

  9. CAD view of MuCap experimental setup e m

  10. the 10 bar Hydrogen TPC wires on glass frames - pure metallic & ceramic structures bakeable to 130C ultra-pure protium gas el. drift field 2 kV/cm vdrift = 0.5 cm/μs UHV = 30 kV Ucath = 5-6 kV MWPC readout in x-z bottom planes sensitive volume (12 x 15 x 30) cm3

  11. high gas purity maintained by continuous circulation - operated by cryogenic adsorption/desorption cycles in active Carbon - traps all higher Z impurities by Zeolites immersed in liquid Nitrogen our main impurity is water vapor outgasing from walls & materials

  12. control & calibrations of impurities event display showing impurity capture event humidity of TPC protium was monitored with PURA device ~17 ppb reached 35 strips  75 anode wires  H2O test admixing of 21 ppm N2: cleaned off to <10 ppb N2   time axis (60 μs)  

  13. HD separation column constructed in Gatchina & PSI, tested & operated in March/April 2006 principle: - H2 gas circulates from bottom to top & gets liquified at the cold head - liquid droplets fall down & evaporize  gas phase depleted from D - the D-enriched liquid H2 at the bottom is slowly removed results of AMD analysis at ETHZ: protium in 2004/5: cd = (1.45±0.15)10-6 protium used in 2006 after HD separation: cd < 6*10-9 (6 ppb)

  14. final 2004 lifetime fit (1.6*109 good μ- events) • chosen impact cut 120 mm ( small μd correction!) • λμ- = 455‘851.4 ± 12.5stat ± 8.5syst s-1 (main MuCap result) • λμ+ = 455‘162.2 ± 4.4s-1 (new world average incl. μLAN) • 455’164 ± 28 (MuCap result with 0.6*109μ+events) •  μ- lifetime curves 2004 data resulting μp capture rate: • ΛS = 725.0  17.4 s-1 • theory (+ radiative corr.): • ΛS = 710.6  3 s-1

  15. gP vs λOP plot with first unambiguous MuCAP result our result is gP = 7.3±1.1(HBChPT: 8.26±0.23) gP TRIUMF  SACLAY  λop

  16. final MuCap analysis • data statistics result / errors: stat. syst. total • 1.6 * 109ΛS = 725.0± 13.7 ± 10.7 ± 17.4 s-1 (2.4%) • (published)gP = 7.3 ± 1.1 (15%) • 2005-07 1.8 * 1010 expect δΛS to ± 3.7 ± 4 ± 5.5 s-1 (0.8%) • (analysis in progress)δgP to ± 0.35 (5%)(HBChPT: 8.26±0.23) • *************************** • list of systematic errors [s-1]: • topic 20042005-07 method of improvement • Z>1 impurities 5.2 2 improved CHUPS-system, FADC • μd diffusion 1.6 <0.1isotope separator (cd < 6 ppb) • analysis methods 6.6 3 improved analysis programs, MC • ppμ form. rate (Λppμ) 5 0.5 measurement (Argon doped run) • ortho-para rate (λOP) 3.5 2 measurement of neutron spectra • --------------------------------------------------------- • sum of syst. errors 10.7 s-14 s-1 • completion of final analysis in 2009

  17. Argon doped run forΛppμmeasurement - protium run with 20 ppm Argon doping - electron spectrum 5.5*108 events - neutrons from μAr capture 3*105 events - tpc data from μ-Ar capture 4*106 evts combined analysis of time spectra yields λcaptAr , λtransferpAr , λppμ to ~2% reduces error of ΛS to 0.5 s-1 ! (analysis in progress at Urbana) e- time spectrumyields λe neutron time spectrum Ar capture time spectrum

  18. authors of first μp capture results published in Phys. Rev. Letters 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. 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), 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

  19. the MuSun experiment nuclear muon capture on the deuteron there are new challenges compared to μp capture: - at room temperature the μd spin state is badly known due to slow spin flip rate and strong ddμ formation + fusion (see kinetics) - transfer rates to impurities are significantly larger technical solution: go to low temperatures (~30 K) And higher gas density (5-10% of liquid, up from 1%)  Λ(μd3/2  μd1/2) ~ 3x106s-1  impurities (H2O, etc) freeze out

  20. μ + t + p μd↑↓ μd↑↑ μ + 3He + n dμd μ3He + n μZ ΛD n + n + ν μd kineticsslow spin flip and resonant dμd fusion cycles μ

  21. effect of ddμ kinetics • at low density φ=1%, 300K • (as μp capture experiment): • - spin flip very slow • rate not precisely known (±15%)  no precise interpretation of observed capture rate possible at higher density (φ=5-10%), 30K (proposed for μd capture experiment): • - strong depopulation of quartetstate • observable in dμd fusion time spectrum  pure μd(F=1/2) state capture rate highest (~400s-1) conclusion: develop cryo-tpc for μd experiment 1% LD2300 K md() md() m3He time (ms) 30K, 5% 10% LD230 K

  22. setup of MuSun detector e eSC ePC2 ePC1 mPC Cryo-TPC m mSC

  23. technical design of the cryo-system liquid Neon cooling circuit (vibration free) continuous cleaning by CHUPS

  24. CAD view of cryo tpc, vacuum & cooling system

  25. outlook • Nov 2008 first test run using still the MuCap setup (300K) • 10 bar high purity deuterium • charge collection on 8x10 cm2 pad plane • studies of: • - impurity events, controls, cleaning • - ddμ fusion events • - measure μ transfer rate to impurities • - neutron spectra • - fall 2009 commissioning run with new cryo tpc at 30K • - 2010-11 main statistics runs ~2*1010 events

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