µp & µ 3 He capture rates and Induced pseudo-scalar coupling of proton weak interaction

1. µp & µ3He capture rates and Induced pseudo-scalar couplingof proton weak interaction A.Vorobyov Petersburg Nuclear Physics Institute

2. PSI meson factory 600 MeV protons 2 mA extracted proton beam 100% duty factor High intensity muon channels Muon-on-request mode PNPI in PSI since 1986 • Muon catalyzed dd-and dt-fusion experiments(completed) • Muon capture on He-3(competed) • Muon capture on proton (data taking completed, first results published) • Muon capture on deutron (experiment under preparation)

3. MuCap collaboration 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, BelgiumTU München, Garching, GermanyUniversity of Kentucky, Lexington, USABoston University, USA

4. Muon Capture on Proton - + p  (µ-p)1S→ µ+ n BR=0.16% ΛS MuCap goal:to measure µp-capture rateΛSwith 1% (or better) precision p n qc2 = - 0.88 mµ2 W νµ µ gv = 0.9755(5) values and q2 dependence known from EM gM = 3.5821(25) form factors via CVC gA = 1.245(4) gA(0)=1.2695(29) from neutron β-decay, gP(theory) = 8.26 ±0.23q2 dependence from neutrino scattering gP(expt) = ? ( ( µp-capture offers a unique probe of the nucleon’s electroweak axial structure

5. gpNN n p p Fp m- nm Theoretical predictions for gP •Partial conservation of axial current (PCAC) • Heavy Barion chiral perturbation theory (ChPT) W gP= (8.74  0.23) – (0.48  0.02) = 8.26  0.23 PCAC pole term ChPT leading order one loop two-loop <1% Recent reviews:V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31

6. Sensitivity of ΛS to form factors Contributes 0.45% uncertainty to measured S Theory predicts gP with ~ 3% precision Uncertainties in other form factors set the limit : =0.45% or =3% To approach this limit, one should measure ΛS with ~0.5% precision Examples: 10% 56% 1.0% 6.1% 0.5% 3.8%

7. ppμ ppμ LT = 12 s-1 triplet (F=1) pμ↑↑ Lortho=506s-1 Lpara=200s-1 λop μ ppμ ppμ f λppm ortho (J=1) para (J=0) pμ↑↓ singlet(F=0) LS= 710s-1 From which muonic state the muon capture occurs ? n+n

8. 1 % LH2 100% LH2 pm ppμ ppmO ppμ pm ppmO ppmP ppmP time (ms) LT = 12 s-1 triplet (F=1) pμ↑↑ Lortho=506s-1 Lpara=200s-1 λop μ ppμ ppμ f λppm ortho (J=1) para (J=0) pμ↑↓ singlet(F=0) LS= 710s-1 n+n

9. ppμ ppμ LT = 12 s-1 triplet (F=1) pμ↑↑ Lortho=506s-1 Lpara=200s-1 λop μ ppμ ppμ f λppm ortho (J=1) para (J=0) pμ↑↓ singlet(F=0) LS= 710s-1 Muon capture in liquid H2 deals with uncertain muonic molecular state The H2 gas pressure should not exceed 10 bar to provide dominant (µ-p)1Sstate n+n

10. Status of µp-capture experiments Two experimental methods to measure ΛC Neutron detection Life time measurement CPT inv - + p  µ+ n µ± → e± νe νµ ΛC Nn/Nµ ΛC = 1/τµ+ - 1/τµ- *) First direct observation of µp-capture

11. Status of µp-capture experiments - + p  µ+ n BR = 0.16% Ordinary muon capture, OMC Radiative muon capture, RMC - + p  µ+ n + γBR = 10-8 RMC is more sensitive to gP (by a factor of 3) than OMC but huge problems due to small BR. One RMC experiment in TRIUMPH (1996)

12. Precise Theory vs. of Exp. Efforts gP - + p m+ n @ Saclay - + p m+ n + g@TRIUMF ChPT mCapprecisiongoal TRIUMF 2006 exp theory lOP(ms-1)

13. Pioneers of muon capture experiments 1969 Bologna-Pisa-CERN Emilio Zavattini 1927-2007 H2 –target 8 atm gp≈ 11 ± 5 1973 Dubna group H2 –target 41 atm Δgp = ± 7 Expt. Problems • Wall effects • Background • Neutron detection efficiency

14. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm

15. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm • Lifetime method ΛS = 1/τµ+ - 1/τµ- 10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

16. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm • Lifetime method ΛS = 1/τµ+ - 1/τµ- 10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1% >1010 muon decayevents High data taking rate

17. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm • Lifetime method ΛS = 1/τµ+ - 1/τµ- 10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1% >1010 muon decayevents High data taking rate • Ultra clean protium impurities with Z>1 less than 10 ppb (1 ppb = 10-9) deuterium concentration less than 100 ppb

18. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm • Lifetime method ΛS = 1/τµ+ - 1/τµ- 10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1% >1010 muon decayevents High data taking rate • Ultra clean protium - impurities with Z>1 less than 10 ppb (1 ppb = 10-9) - deuterium concentration less than 100 ppb • Clean muon stop selection No wall effects

19. Strategy of MuCap experiment (µ-p)1S • H2 gas target at 10 atm • Lifetime method ΛS = 1/τµ+ - 1/τµ- 10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1% >1010 muon decayevents High data taking rate • Ultra clean protium impurities with Z>1 less than 10 ppb (1 ppb = 10-9) deuterium concentration less than 100 ppb • Clean muon stop selection No wall effects • Low background < 10-4

20. Time projection chamber, TPC -40kV µ E ………………… . . . . . . . . . . . . G +5kV G Cathode strips Anode wires Sensitive volume 15 x 12 x 28 cm3 Muon stop selection inside the sensitive volume far enough from all chamber materials 3D detection of muon track X- cathode strips Y- drift time Z- anode wires Y y x x z z

21. eSC hodoscope ePC2 ePC1 e µSC -40kV µ E ………………… . . . . . . . . . . . . G +5kV G Cathode strips Anode wires tµ = t eSC – t µSC e-µ space correlation eliminates background

24. Display of a µ→eννevent detected in TPC

25. Chemical purity control of hydrogen gas • Self-control for Z>1 contaminations by recoil detection in TPC. Sensitivity 10 ppb. • Chromotography CN2, CO2. Sensitivity 10 ppb • Humidity control device. Sensitivity 3 ppb µZ-capture rate measured in TPC CZ increases by 0.1 ppm per day Display of a µp → µZ→ n + recoil event detected by TPC

26. Cryogenic circulation-purification hydrogen gas system N2 less than 10 ppb O2 less than 10 ppb H2O about 10 ppb Gas purification system

27. Isotopic purity of protium Deuterium concentration in hydrogen gas Natural gas 140 ppm Best on market 2 ppm Produced for MuCap ≤ 6 ppb Accelerator mass spectrometry at ETH in Zurich Reached sensitivity 6 ppb Cryogenic isotopic exchange column

28. Gas purification system Hydrogen isotopes separation column

29. Kicker Plates m detector m- TPC +12.5 kV -12.5 kV 50 ns switching time Data taking rate PSI muon channel can provide ~ 70 kHz muons MuCap could use only ~ 7kHz (to prevent pile up) New beam system (Muon-on-demand) constructed in 2005 allowed to increase the usable beam intensity up to 20 kHz ~3 times higher rate run2006 Muon-on-demand system Beam at TPC entrance 20 kHz Rate of selected µ→eνν events 4kHz Statistics of selected events 3·108 /day 1010 events ~for a two month run Fast (dead time free) read out system

30. Reduction of background by µ-e vertex cut e µ The impact cut can reduce the background to a level of 10-4-10-5

31. Statistics of selected events Only 2004 data are analyzed at present (~10% of total statistics) The results are published in PRL 99,032002(2007)

32. µ- and µ+ disappearence rates from 2004 data *) including last MuLan data λµ- = (λµ+ + ∆λµp) + ΛS + ∆Λpµp ∆λµp = -12.3 s-1 bound state correction ∆Λpµp = - 23.5 ± 4.3 ± 3.9 s-1 µ- captures from pµp molecules ΛS = 725.0 ± 13.7 ± 10.7 s-1

33. MuCap ΛS = 725.0 ± 13.7 ± 10.7 s-1 Comparison with theory Average of HBChPT calculations of S: Apply new rad. correction (2.8%): A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007 MuCap Th MuCap Th gp = gp + δgp/δΛS( ΛS - ΛS ) = 7.3 ± 1.1 δgp/δΛS = - 0.065 s gP = 7.3 ± 1.1 gP = 8.2 ± 0.2 HBChP theory MuCap 2007

34. - + p  m + n + g MuCap agrees within 1σ with the Heavy Barion Chiral Perturbation Theory Further analysis of the MuCap data should decrease the experimental error by a factor of three

35. An extract from an article commenting the MuCap results “That agreement would seem to close a confusing chapter in nuclear physics which has seen decades of disagreement regarding the value of gp expt. It would be interesting to watch continuing improvements in the MuCap results.” A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007

36. Muon Capture on He-3 µ- + 3He → 3H + νµ Et = 1.9 MeV TPC operating in ionization mode at 120 bar of clean 3He Λstat = 1496 ± 4 s-1 Physics Letters B417,224 1998) The precision of previous data was improved by a factor of 50 Since then, this result was a subject of various analyses with the goal to obtain the value of gp

37. Muon Capture on He-3 Elementary particle model (Kim,Primakoff,1965) FV(qC2)) = 0.834 (11) FM(qC2) = -13.969 (52) FA(qC2) = 1.052 (10) extrapolated from FA(0) = 1.212(5), tritium beta-dacay qC2 = -0.954 mµ2 FP (expt) = 20.8 ± 2.8 FP PCAC = 20.7 Surprisingly good agreement with PCAC

38. Muon Capture on He-3 Impulse approximation model Three body wave function Meson Exchange Currents Latest analysis A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007 gPexpt(µ3He) = 8.7 ± 0.6 This value agrees with our result from the µp-capture experiment gPexpt(µp) = 7.3 ± 1.1 This agreement may be considered as an indication of validity of the theoretical approach used to treat the µ3He capture process

39. Future Complete analysis of the MuCap data. Expectations: δΛS/ΛS ≤1.0 % ΔgP ≤ 6 % 1. Prepare new experiment to measure muon capture rate on deuterium µ + d  n + n + ν with ~ 1% precision. 2. Similar to basic solar fusion reactions p + p  d + e+ +   + d  p + p + e-  + d  p + n + 