Muon Capture on the Proton Final results from the MuCap experiment

1. Muon Capture on the ProtonFinal results from the MuCap experiment Peter WinterUniversity of Washington for the MuCap collaboration  gP

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

3. Nucleon form factors - + pn +  -  q2 = -0.88m2 u d u u d d

4. Nucleon form factors - + pn +  -  q2 = -0.88m2 p n M ~ GFVud · (1-5) · n(V-A)p Observable: Singlet capture rate LS

5. dgP  gP dLS 1.0% 6.1% LS Contributes 0.45% uncertainty to LStheory Nucleon form factors M ~ GFVud · (1-5) · n(V-A)p V = gV(q2)  + i gM(q2) q/2MN A = gA(q2) 5 + gP(q2) q/m5

6. Pseudoscalar form factor gP 2mNm¹gA(0) 2mNmgA(0) 1 gP(q2) = - -gA(0)mNmrA2 gP(q2) = -   q2-m¼2 q2-m2 3 f  gNN p n NLO (ChPT) Bernard, Kaiser, MeissnerPR D50, 6899 (1994) PCAC pole term (Adler, Dothan, Wolfenstein) gP = 8.26 ± 0.23 • ChPT based on the spontaneous symmetry breaking • solid QCD prediction via ChPT (2-3% level) • basic test of chiral symmetries and low energy QCD Recent review: Kammel, P. and Kubodera, K., Annu. Rev. Nucl. Part. Sci. 60 (2010), 327

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

8. Muon capture - Ordinary muon capture (OMC): m- p nn - Radiative muon capture (RMC): m- p nn gBR = ~10-8 for Eg>60 MeV -m- 3He n 3H or other nuclei

9. Muon capture - Ordinary muon capture (OMC): m- p nn - Radiative muon capture (RMC): m- p nn gBR = ~10-8 for Eg>60 MeV -m- 3He n 3H or other nuclei

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

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

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

13. f: Hydrogen density, (LH2: f=1) pμ↑↑ LT ~ 12s-1 p μ- f>0.01 <100ns pμ↑↓ S ~ 700s-1 Muon kinetics

14. ppμ LOM ~ ¾ LS ppμ flOF ortho (J=1) pμ↑↓ lOP flPF LPM ~ ¼ LS para (J=0) LS ~ 700s-1 Muon kinetics • ppm formation depends on density f • Interpretation requires knowledge of lOF and lOP

15. ppμ LOM ~ ¾ LS ppμ flOF ortho (J=1) pμ↑↓ lOP flPF LPM ~ ¼ LS para (J=0) LS ~ 700s-1

16. ppμ LOM ~ ¾ LS ppμ flOF ortho (J=1) pμ↑↓ lOP flPF LPM ~ ¼ LS para (J=0) LS ~ 700s-1 Muon kinetics Lower density dramatically decreases sensitivity to molecular complications

17. Previous results m p  n n @ SACLAY m p  n n g @ TRIUMF gP ChPT mCapprecisiongoal TRIUMF 2005 exp theory lOP (ms-1) • no overlap theory, OMC & RMC • large uncertainty in lOP gP± 50%

18. ppμ LOM ~ ¾ LS ppμ flOF ortho (J=1) cdlpd pμ↑↓ lOP μd flPF LPM ~ ¼ LS Ld para (J=0) LS ~ 700s-1 Requirement of clean target diffusion

19. Deuterium removal unit cd < 6 ppb

20. LZ ~ LS Z4 μZ ppμ LOM ~ ¾ LS ppμ cZLZ flOF ortho (J=1) cdlpd pμ↑↓ lOP μd flPF LPM ~ ¼ LS Ld para (J=0) LS ~ 700s-1 Requirement of clean target diffusion

21. High-Z in MuCap Circulating H2Ultra-Purification System • Active TPC • No materials in fiducial volume cN, cH2O< 10 ppb NIM A578 (2007), 485

22. LZ ~ LS Z4 μZ ppμ LOM ~ ¾ LS ppμ cZLZ flOF ortho (J=1) cdlpd pμ↑↓ lOP μd flPF LPM ~ ¼ LS Ld para (J=0) LS ~ 700s-1 Requirement of clean target diffusion

23. The facility: pE3 beamline at PSI http://www.psi.ch

24. t MuCap e m

25. TPC - the active target • 10 bar ultra-pure H2 • bakeable materials • No materials in fiducial volume

26. TPC - the active target • 10 bar ultra-pure H2 • bakeable materials • No materials in fiducial volume m- E m-p e-

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

28. 10 times increased statistics *V.A. Andreev et al., Phys. Rev. Lett. 99, 03202 (2007) Remember: l+ known to 1 ppm from MuLan!

29. Normalized residuals Lifetime spectra

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 Detune clock Double blinded analysis! Hide from analyzers Analyzers add secret offset

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

38. Imp. Capture: m-Z  (Z-1) n n Impurity monitoring 2004 run: cN < 7 ppb, cH2O~30 ppb 2006 / 2007 runs: cN < 7 ppb, cH2O~10 ppb

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

40. molecular formation bound state effect External corrections to l- LS (MuCapprelim.*) = 714.5 ± 5.4stat± 5.4systs-1 * Small revision of molecular correction might affect LS < 0.5s-1 and syst. error LS(theory) = 711.5 ± 3.5 ± 3 s-1

41. Precise and unambiguous MuCap resultsolves longstanding puzzle gP(MuCap prelim.) = 8.07 ± 0.5 gP(theory) = 8.26 ± 0.23

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

43. Precise and unambiguous MuCap resultsolves longstanding puzzle gP(MuCap prelim.) = 8.07 ± 0.5 gP(theory) = 8.26 ± 0.23