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

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

Muon Capture Experiments in Hydrogen & Deuterium our goal precision measurement of muon capture rates to ±1% 1) μ - + p → (μ - p) ↑↓ → n + ν μ singlet capture rate Λ S sensitive to induced pseudoscalar coupling g P in weak interactions first results published – full analysis in progress 2) μ - + d → (μ - d) ↑↓ → n + n + ν μ doublet capture rate Λ D sensitive to the axial two-body current term L 1A in effective field theories (EFT‘s) in full preparation – first run in Nov 2008

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 p n νeνe e-e- n νμνμ p μ-μ- W W μ - + p  ν μ + n (analogue) heavy baryon chiral perturbation theory (Bernard et al. 1994): g P theory = 8.26  g p least known of the nucleons weak form factors - solid theoretical prediction by HBChPT at 2-3% level - basic test of QCD symmetries

scientific case of μ capture on the deuteron μ + d  n + n + ν μ model-independent connection via EFT & L 1A impact on fundamental astrophysics processes (SNO, pp) 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 calculationscomparison of modern high precision calculations (eff. field theories,standard nucl. physics approach) (eff. field theories,standard nucl. physics approach) EFT: axial current reactions related by single parameter L 1A the muon capture rate on deuteron determines L 1A the muon capture rate on deuteron determines L 1A MEC EFT L 1A

- only n & ν in output channel  limited precision for direct measurement of absolute rates  use lifetime method Λ S = λ (μ - p) – λ (μ + ) measure λ ‘s to 10 ppm >~ events required - capture rate small ~ of λ (μ + )  avoid any wall stops to !  develop ultra-clean TPC as active muon stop target operated in hydrogen gas log(counts) t e -t  μ+μ+ μ – λ   λ   S reduces lifetime by  → e experimental challenges & our strategy (I)

- μ-transfer to impuries (N 2,H 2 O,..) μp + N (O,..) → μN ( μO,..) + p  distortion of lifetime curves develop continuously circulating & cleaning system (CHUPS) goal: c Z ~ (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: c d < (100 ppb) experimental challenges & our strategy (II)

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+ Λ ppμ n+ - pμ ↑↑ depopulates quickly (<100ns) - ppμ molecule formation with ( τ ~ 0.4μs/φ) Λ ppμ known only to ± 20% - ortho to para transition rate badly known λ OP known only to ± 50% - Λ S - Λ OM - Λ PM are all quite different! τ~10ns experimental challenges & our strategy (III) kinetics of μ - in H 2 solution:- use low gas density φ (10 bar H 2 ) ≈ 1% of liquid - determine Λ ppμ by Argon doped run – λ OP from neutron spectra

 e CAD view of MuCap experimental setup

U HV = 30 kV U cath = 5-6 kV MWPC readout in x-z bottom planes sensitive volume (12 x 15 x 30) cm 3 wires on glass frames - pure metallic & ceramic structures bakeable to 130C the 10 bar Hydrogen TPC ultra-pure protium gas el. drift field 2 kV/cm v drift = 0.5 cm/μs

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

control & calibrations of impurities event display showing impurity capture event   time axis (60 μs)   35 strips  75 anode wires  test admixing of 21 ppm N 2 : cleaned off to <10 ppb humidity of TPC protium was monitored with PURA device ~17 ppb reached N2N2 H2OH2O

HD separation column constructed in Gatchina & PSI, tested & operated in March/April 2006 principle: - H 2 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 H 2 at the bottom is slowly removed results of AMD analysis at ETHZ: protium in 2004/5: c d = (1.45±0.15)10 -6 protium used in 2006 after HD separation: c d < 6 * (6 ppb)

final 2004 lifetime fit (1.6 * 10 9 good μ - events) chosen impact cut 120 mm (  small μd correction!) λ μ - = 455‘851.4 ± 12.5 stat ± 8.5 syst s -1 (main MuCap result) λ μ + = 455‘162.2 ± 4.4 s -1 (new world average incl. μLAN) 455’164 ± 28 (MuCap result with 0.6 * 10 9 μ + events)   μ - lifetime curves 2004 data resulting μp capture rate: Λ S =  17.4 s -1 theory (+ radiative corr.): Λ S =  3 s -1

g P vs λ OP plot with first unambiguous MuCAP result our result is g P = 7.3±1.1 (HBChPT: 8.26±0.23) gPgP  λ op  TRIUMF SACLAY

final MuCap analysis data statistics result / errors: stat. syst. total * 10 9 Λ S = ± 13.7 ± 10.7 ± 17.4 s -1 (2.4%) (published) g P = 7.3 ± 1.1 (15%) * expect δΛ S to ± 3.7 ± 4 ± 5.5 s -1 (0.8%) (analysis in progress) δg P to ± 0.35 (5%) (HBChPT: 8.26±0.23) *************************** list of systematic errors [s -1 ]: topic method of improvement Z>1 impurities improved CHUPS-system, FADC μd diffusion 1.6 <0.1 isotope separator (c d < 6 ppb) analysis methods improved analysis programs, MC ppμ form. rate (Λ ppμ ) measurement (Argon doped run) ortho-para rate ( λ OP ) measurement of neutron spectra sum of syst. errors 10.7 s -1 4 s -1 completion of final analysis in 2009

Argon doped run for Λ ppμ measurement e - time spectrum yields λ e neutron time spectrum Ar capture time spectrum - protium run with 20 ppm Argon doping - electron spectrum 5.5*10 8 events - neutrons from μAr capture 3*10 5 events - tpc data from μ-Ar capture 4*10 6 evts combined analysis of time spectra yields λ capt Ar, λ transfer pAr, λ pp μ to ~2% reduces error of Λ S to 0.5 s -1 ! (analysis in progress at Urbana)

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 authors of first μp capture results published in Phys. Rev. Letters 99, (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 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)

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(μd 3/2  μd 1/2 ) ~ 3x10 6 s -1  impurities (H 2 O, etc) freeze out

μd kinetics slow spin flip and resonant dμd fusion cycles μ μd ↑↑ μd ↑↓ dμd μZ ΛDΛD n + n + ν μ 3 He + n μ + 3 He + n μ + t + p

effect of ddμ kinetics time (  s) 30K, 5%  d(  )  d(  )   He 1% LD K 10% LD 2 30 K 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 quartet state - observable in dμd fusion time spectrum  pure μd (F=1/2) state capture rate highest (~400s -1 ) conclusion: develop cryo-tpc for μd experiment

setup of MuSun detector  PC  SC ePC2 ePC1 eSC Cryo-TPC e 

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

CAD view of cryo tpc, vacuum & cooling system

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 main statistics runs ~2*10 10 events