ПРЕЦИЗИОННОЕ ИЗМЕРЕНИЕ СКОРОСТИ ЗАХВАТА МЮОНА В ВОДОРОДЕ И ОПРЕДЕЛЕНИЕ ПСЕВДОСКАЛЯРНОГО ФОРМ ФАКТОРА ПРОТОНА g P PNPI participants in MuCAP collaboration*) : V.A. Andreev, V.A. Ganzha, P. A.Kravtsov, A.G. Krivshich, M.P. Levchenko, E.M. Maev, O.E. Maev, G.E. Petrov, G.N. Schapkin, G.G. Semenchuk, M. A. Soroka, A.A. Vasilyev, A.A. Vorobyov, M.E. Vznuzdaev

- + p (µ - p) 1S µ + n BR=0.16% - + p (µ - p) 1S µ + n BR=0.16% MuCap goal: to measure µp-capture rate Λ S with 1% (or better) precision Muon Capture on Proton ΛSΛS µ νµνµ pn W q c 2 = m µ 2 µp-capture offers a unique probe of the nucleons electroweak axial structure

Muon capture on proton

Стандартная Модель и структура нуклонов g v = ± g a = ± g m = ± g P (th) = 8.26 ± 0.23 g P (OMC)= 6 – 12 g P (RMC) = 12.2 ± 0.9 ± 0.4

50 years of effort to determine gP 88 Radiative muon capture in hydrogen was carried out only recently with the result that the derived gP was almost 50% too high. If this result is correct, it would be a sign of new physics... Lincoln Wolfenstein (Ann.ReNucl.Part.Sci. 2003) OMC RMC - + p n + + Kammel&Kubodera

Emilio Zavattini Bologna-Pisa-CERN 1973 Dubna group H2 –target 8 atm Pioneers of muon capture experiments H2 –target 41 atm g p = 11.0 ± 3.8 Expt. Problems Wall effects Background Neutron detection efficiency g p =8.7 ± 5.7

T = 12 s -1 pμ singlet (F=0) S = 712 s -1 n+ triplet (F=1) μ pμ ppμ para (J=0)ortho (J=1) λop ortho =506 s -1 para =200 s -1 ppμ pp P pp O p 100% LH 2 p pp P pp O 1 % LH 2 time ( s) λpp

Стратегия MuCap эксперимента Измерение времени жизни ( с точностью 10ppm, регистрация e распадов ( 10^10) Однозначность интерпретации захват из F=0 состояния p атома при плотности 1% LH2 Использование методики активной мишени (TPC) с точной регистрацией координат и времени остановок мюонов, реконструкция треков электронов к точке распада. Использование ультрачистого водорода Cz < 10ppb Контроль примесей по реакциям: p + Z Z + p, Cz~10ppb. Обеспечение изотопической чистоты водорода p + d d + p + 134eV, примесь Cd

PSI meson factory 600MeV protons 2mA extracted proton beam 100% duty factor High intensity muon channels Muon-on-request mode Muon catalyzed dd-and dt-fusion experiments ( completed ) Muon capture on He-3 ( completed ) Muon capture on proton ( completed ) Muon capture on deuteron ( in progress ) PNPI in PSI since 1986

Schematic view of the TPC The trajectories of charged particles are measured in 3D space with resolution (rms) 1-2 mm.

The signal on TPC anode wires from -e decay event

Display of a typical event with -capture reaction on impurity

IV. the new protium isotope separation facility: production of ultra-depleted protium 1) Cd = 1440 ppb (2004) 2) Cd < 60 ppb (2006) 3) Cd < 6 ppb (2007)

Muon-On-Demand concept Beamline Single muon requirement (to prevent systematics from pile-up) limits accepted rate to ~ 7 kHz, while PSI beam can provide ~ 70 kHz kV kV Kicker Plates 50 ns switching time detector TPC Fig will be improved ~3 times higher rate dc kicked 2-Dec-2005 Lan kicker TRIUMF rf design

Lifetime spectra Normalized residuals

Общая набранная статистика Год μ+ (10^ 9) μ- (10^ 9) Cd(ppb) H2O(ppb) ~1400 ~ ~

TABLE: Applied corrections and systematic errors. Effect Corrections and uncertainties [s-1] R06 R07 Z > 1 impurities mu-p scatter removal mu-p diffusion mu-d diffusion Fiducial volume cut Entrance counter ineff Electron track def Total corr. λ μ =========================================================== mup bound state ( D μp ) ppmu states (D ppμ )

Результаты анализа данных за год N μ- = х λ μ- = ± 12.5stat ± 8.5syst s -1 (MuCAP 2004). λ μ- = ± 7.7stat ± 5.1syst s -1 (MuCAP 2006). λ μ- = ± 8.3stat ± 3.9syst s -1 (MuCAP 2007).

Muon Capture Rate λ s λ s = λ μ- -(λ μ+ - D μp ) + D ppμ D μp = 12.3 s-1 ( μp bound state ) D ppμ = 17.7 s-1 ( λppμ =(1.94 ± 0.06) μ s-1)

Результаты анализа данных за год λ μ+ = ± 0.46 s -1 (μLAN experiment) λ μ- = ± 5.4stat ± 4.7syst s -1 (MuCap ) Λ S MuCap (aver.) = ± 5.4stat ± 5.3syst s -1 Λ S Th = s -1 (aver.) s -1 (r.c.)=712.7± 3.0 ± 3.0 s -1 g P MuCap = g P Th x (Λ S MuCap - Λ S Th ) g P MuCap = 8.06±0.48(exp)±0.28(th) g P Th = (2.8%)

Precise and unambiguous MuCap result solves longstanding puzzle gP(theory) = 8.2 ± 0.2gP(theory) = 8.2 ± 0.2

MuCap collaboration 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 TU München, Garching, Germany University of Kentucky, Lexington, USA Boston University, USA

Earlier, in 1998, we have studied the muon capture on 3 He. The muon capture rate in the channel μ He 3 H + ν μ was measured with high precision : Λ c = ± 4.0 s -1 (0.3% ). This result have been used in some theoretical analyses : L.E. Marcucci et al. (2012) [1] and D. Gazit( 2009) [2] for deriving the Λ c and the protons pseudoscalar form factor g P. Λ c = 1494 ± 21s -1 [1] and Λ c = 1499± 12 s -1 ([2]. g P = 8.13 ± 0.6 [2]