1. Muon Capture on the Proton Final results from the MuCap experiment Muon Capture on the Proton Final results from the MuCap experiment gPgP Peter Winter University of Washington  for the MuCap collaboration 

2. Overview Brief motivation for MuCap Experimental overview Final MuCap result

3. --  - + p  n + q 2 = -0.88m  2 Nucleon form factors u u d d u d

4. -- pn  - + p  n + M ~ G F V ud ·    (1-  5 )   ·  n (V  -A  )  p q 2 = -0.88m  2 Nucleon form factors Observable: Singlet capture rate  S

5. Nucleon form factors V  = g V (q 2 )   + i g M (q 2 )   q  /2M N M ~ G F V ud ·    (1-  5 )   ·  n (V  -A  )  p A  = g A (q 2 )    5 + g P (q 2 ) q  /m   5 Contributes 0.45% uncertainty to  S theory  gPgPgPgP gPgPgPgP  S SSSS 1.0% 6.1%

6. ChPT based on the spontaneous symmetry breakingChPT based on the spontaneous symmetry breaking solid QCD prediction via ChPT (2-3% level)solid QCD prediction via ChPT (2-3% level) basic test of chiral symmetries and low energy QCDbasic test of chiral symmetries and low energy QCD Pseudoscalar form factor g P g P (q 2 ) = - - g A (0)m N m  r A 2 2m N m ¹ g A (0) q 2 -m ¼ 2 1 3 g P (q 2 ) = - 2m N m  g A (0) q 2 -m  2 PCAC pole term (Adler, Dothan, Wolfenstein) NLO (ChPT) Bernard, Kaiser, Meissner PR D50, 6899 (1994) g P = 8.26 ± 0.23  pn  g  NN ff Recent review: Kammel, P. and Kubodera, K., Annu. Rev. Nucl. Part. Sci. 60 (2010), 327

7. How to access g P ? In principle any process directly involving axial current: -  decay: Not sensitive since g P term proportional to q - scattering difficult to measure Muon capture most direct source for g P 

8. Muon capture - Ordinary muon capture (OMC):  - p  n - Radiative muon capture (RMC):  - p  n  BR = ~10 -8 for E  >60 MeV -  - 3 He   3 H or other nuclei

9. Muon capture - Ordinary muon capture (OMC):  - p  n - Radiative muon capture (RMC):  - p  n  BR = ~10 -8 for E  >60 MeV -  - 3 He   3 H or other nuclei

10. Methods to measure OMC rate Direct method: - Measure outgoing neutrons - Typical experiments ~10% precision in  S Lifetime method:  S  - - +  S = 0.15% - !

11.  + known to 1 ppm! D.B. Chitwood et al., Phys. Rev. Lett. 99, 03201 (2007) D. Webber et al., Phys. Rev. Lett. 106, 041803 (2011) MuLan 2007 and 2011 G F = 1.1663818(7) x 10 -5 GeV -2 (0.6 ppm)

12. MuCap key elements Lifetime methodLifetime method Low gas densityLow gas density Active gas target (TPC)Active gas target (TPC) Ultra pure gas system with in-situ monitoringUltra pure gas system with in-situ monitoring Isotopically pure hydrogen gasIsotopically pure hydrogen gas

13.  Hydrogen density, (LH 2 :  =1) Muon kinetics μ- pμ ↑↑ pμ ↑↓ p  T ~ 12s -1  S ~ 700s -1  >0.01 <100ns

14. Muon kinetics pp  formation depends on density  pp  formation depends on density  Interpretation requires knowledge of OF and OP Interpretation requires knowledge of OF and OP pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S

15. pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S

16. pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S Muon kinetics Lower density dramatically decreases sensitivity to molecular complications

17. Previous results OP (ms -1 )  Cap precision goal exp theory TRIUMF 2005  p  n @ SACLAY  p   n  @ TRIUMF gPgP no overlap theory, OMC & RMC no overlap theory, OMC & RMC large uncertainty in OP  g P ± 50% large uncertainty in OP  g P ± 50% ChPT

18. Requirement of clean target pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S μd c d c d pd dd diffusion

19. Deuterium removal unit c d < 6 ppb

20. Requirement of clean target pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S μd c d c d pd μZ cZcZZcZcZZ dd  Z ~  S Z 4 diffusion

21. High-Z in MuCap c N, c H2O < 10 ppb Circulating H 2 Ultra-Purification System NIM A578 (2007), 485 Active TPC No materials in fiducial volume

22. Requirement of clean target pμ ↑↓  S ~ 700s -1 OP ortho (J=1) ppμ   OF para (J=0) ppμ   PF  OM ~ ¾  S  PM ~ ¼  S μd c d c d pd μZ cZcZZcZcZZ dd  Z ~  S Z 4 diffusion

23. The facility:  E3 beamline at PSI http://www.psi.ch

24.  e MuCap t

25. TPC - the active target 10 bar ultra-pure H 210 bar ultra-pure H 2 bakeable materialsbakeable materials No materials in fiducial volumeNo materials in fiducial volume

26. TPC - the active target 10 bar ultra-pure H 210 bar ultra-pure H 2 bakeable materialsbakeable materials No materials in fiducial volumeNo materials in fiducial volume -p-p E e-e- -- 26

27. A sample event TPC active volume Fiducial volume Front face view muon beam direction vertical direction TPC side view transverse direction vertical direction

28. 10 times increased statistics YearStatistics [10 10 muon decays] Comment -- ++ 20040.160.05published * 20060.550.16This talk 20070.500.40This talk Total~1.21~0.61  Remember: + known to 1 ppm from MuLan! *V.A. Andreev et al., Phys. Rev. Lett. 99, 03202 (2007)

29. Lifetime spectra Normalizedresiduals

30. Consistency checks

31. Consistency: Rate versus run Data run number (~3 minutes per run)

32. Rate versus azimuth

33. Blinded measurement 500 MHz precise master clock Analyzers add secret offset Double blinded analysis! Detune clock Hide from analyzers

34. Double blinded ~700 s -1

35. Relative unblinded ~700 s -1 rates with secret offset, stat. errors only

36. Unblinded ~700 s -1

37. Systematic corrections and errors Systematic errorsRun 2006Run 2007Comment (s -1 )  (s -1 ) (s -1 )  (s -1 ) High-Z impurities -7.81.87-4.540.93  p scatter -12.43.22*-7.201.25** = prelim.  p diffusion -3.10.1-3.00.1 Fiducial volume cut 33 Entrance counter inefficiencies 0.5 Choice of electron detector def. 1.8* * =prelim. Total -23.35.14 § -14.743.88 §§ = correlated

38. Impurity monitoring 2004 run: c N < 7 ppb, c H2O ~30 ppb 2006 / 2007 runs: c N < 7 ppb, c H2O ~10 ppb Imp. Capture:    Z  (Z-1) n

39. Final high-Z impurity correction 0 Production DataCalibration Data (oxygen added to production gas) Extrapolated Result Observed capture yield Y Z Lifetime deviation is linear with the Z>1 capture yield.

40. External corrections to - molecular formation bound state effect  S (MuCap prelim.*)  714.5 ± 5.4 stat ± 5.4 syst s -1  S (theory) = 711.5 ± 3.5 ± 3 s -1 * Small revision of molecular correction might affect  S < 0.5s -1 and syst. error

41. Precise and unambiguous MuCap result solves longstanding puzzle g P (theory) = 8.26 ± 0.23 g P (MuCap prelim.) = 8.07 ± 0.5

42. Subset of the MuCap collaboration Boston UniversityBoston University Regis University, ColoradoRegis University, Colorado Université Catholique de Louvain, BelgiumUniversité Catholique de Louvain, Belgium James Madison UniversityJames Madison University Petersburg Nuclear Physics Institute, Gatchina, RussiaPetersburg Nuclear Physics Institute, Gatchina, Russia Paul Scherrer Institute, CHPaul Scherrer Institute, CH University of CaliforniaUniversity of California University of Illinois at Urbana-ChampaignUniversity of Illinois at Urbana-Champaign University of WashingtonUniversity of Washington University of KentuckyUniversity of Kentucky Supported by NSF, DOE, Teragrid, PSI and Russian Acad. Science and CRDF

43. Precise and unambiguous MuCap result solves longstanding puzzle g P (theory) = 8.26 ± 0.23 g P (MuCap prelim.) = 8.07 ± 0.5