1 / 34

David Hertzog University of Washington

F inal MuLan and MuCap determinations of the Fermi constant and the nucleon’s weak-induced pseudoscalar coupling. David Hertzog University of Washington. measurements @ 1 – 10 part-per-million precision. CIPANP 2012. m -. Z. Positive and Negative Muon Lifetimes. e -.

garret
Download Presentation

David Hertzog University of Washington

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Final MuLanand MuCap determinations of the Fermi constant and the nucleon’s weak-induced pseudoscalar coupling David Hertzog University of Washington measurements @ 1 – 10 part-per-million precision CIPANP 2012

  2. m- Z Positive and Negative Muon Lifetimes e- • Free muondecay is a pure weak process … • determines Gm, often called GF m+ • Muons stopped in matter: • Positive muonsdecay “as if” free, or form atomic-bound muonium … with a lifetime shift expected at the ~ ppb level •  most precise Fermi Constant • Negative muonsform “1-electron-like” muonic atoms and either decay or, undergo nuclear capture. • The decay and capture rates add; lifetime is “shorter” Extract physics here

  3. Contains all weak interaction loop corrections Dq The Fermi constant is related to the electroweak gauge coupling g by In the Fermi theory, muon decay is a contact interaction where Dq is phase space and both QED and hadronic and radiative corrections In 1999, van Ritbergen and Stuart completed full 2-loop QED corrections reducing the uncertainty in GF from theory to < 0.3 ppm (it was the dominant error before)

  4. Positive muon lifetime motivation:Predictive power of the SM depends on well-measured input parameters GFa MZ 9 ppm 0.37 ppb23 ppm 0.6 ppm Hanneke, Fogwell, Gabrielse PRL 100, 120801 (2008) Phys.Rept.427:257-454,2006 MuLan Collaboration PRL 106, 041803 (2011) This work GF= 1.166 378 8(7) x 10-5 GeV-2 MZ = 91.1875 ± 0.0021 GeV α−1 = 137.035 999 084 ± 0.000 000 051

  5. u gm(1-g5) Negative muon lifetime motivation:Muon capture  Elusive hadronic properties d W m n EM FF’s CVC = 0 n-decay nucleon level quark level -  q2 = -0.88m2 p n G-parity 6

  6. Well known terms contribute ~0.45% uncertainty to LStheory The observable is the Capture Rate LS … … which depends on the form factors gV, gM, gA, gP. gP. is by far the least well known typically ~ 50% prior to this work Therefore: Measure Obtain:

  7. Pseudoscalar form factor gP 2mNmgA(0) 2mNm¹gA(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 LS = 711.5 ± 4.6 s-1(0.65%) • ChPT based on the spontaneous symmetry breaking • QCD prediction via ChPT@ 2-3% precision 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

  8. The experimental determinations of gP prior to MuCap were far less precise Ordinary Muon Capture (OMC) Radiative LH2 LH2 LH2 LH2 GH2 GH2 LH2 LH2 Liquid H2 target Gas (low density) H2 target

  9. Our method: Take difference between tm+ and tm- in hydrogen to infer singlet capture rate LS 1.0 ppm MuLan ~15 ppm MuCap log(counts) μ+ μ – time

  10. The Experiments Generic design considerations MuLan MuCap

  11. Design Considerationscounts and systematic control Need: 1012m+ decays (1 ppm) &1010m-decays (10 ppm) • PSI: • 2.2 mA protons @ 590 MeV • pE3 low-energy muon beamline • Time structured custom Kicker • MuLan: • ~107m+ /s • Beam-on / Beam-off periodic cycles • Multiple decays per cycle • MuCap: • ~105m-/s • Muon-on-demand • 1 measurement at a time

  12. Generic Design Considerationscounts and systematic control • Gain stability • Pileup • Spin (mSR) • Symmetry; Dephasing Stability of Detector “early-to-late” Minimize precession amplitude Maximize precession frequency Background: small and constant • Avoid impurities • Fiducial volume • Interference of m & e tracks Capture rate  must stop in target a TPC specific effect

  13. Extinction ~ 1000 Accumulation Measuring Period 450 MHz WaveForm Digitization The MuLan experimental concept… 170 Inner/Outer tile pairs Real data Kicker On Measurement Period Number (log scale) time Fill Period -12.5 kV 12.5 kV Detector has symmetric design around stops

  14. Stopping targets selected to control spin Quartz AK-3 Internal B ~ 0.5 T AK-3* • Internal 0.5 T transverse field • Precess rapidly • Dephase owing to different arrival times Quartz • Form muonium 90% • Precession period few ns • Control 10% free muon spins by symmetry of detector Halbach Array + Quartz Start Accumulation Start Measurement *Arnokrome-3 (~28% chromium, ~8% cobalt, ~64% iron)

  15. Normal Time Distribution Pileup Time Distribution Leading order pileup is a ~5x10-4 effect, yet … • Statistically reconstruct • pileup time distribution • Fit corrected distribution Fill i Fill i+1 Final deadtime corrected lifetime A slope exists due to a pileup undercorrection 1/t– 2/t 1 ppm 2/t 150 ns deadtime range Extrapolation to 0 deadtime is correct answer

  16. The MuCapExperimental Concept • Stop in pure hydrogen (gas) • Gas impurities < 10 ppb • Isotopic impurity < 6 ppb • Image muon stop with TPC • Measure the disappearance rate (effective lifetime) m- E m-p e-

  17. f: Hydrogen density, (LH2: f=1) pμ↑↑ LT ~ 12s-1 ppμ LOM ~ ¾ LS ppμ flOF p ortho (J=1) μ- < 100ns lOP pμ↑↓ flPF LPM ~ ¼ LS para (J=0) S ~ 700s-1 Muon kinetics

  18. ppμ ppμ flOF ortho (J=1) pμ↑↓ lOP flPF LS ~ 700s-1 para (J=0) Capture from mp singlet is in competition with capture from ppm molecular states: depends on density and time LOM ~ 540 s-1 RMC OMC LPM~ 210 s-1 Liquid hydrogen experiments Molecular-states dominate MuCap conditions Singlet-state dominates

  19. Analysis & Results ? MuLan MuCap

  20. ppm tm + Dsecret 22 ms tau vs fit start time Red band is the set-subset allowed variance MuLan fit of 30,000 AK-3 pileup-corrected runs Relative t (ppm) 0 9 ms

  21. Start-time scan Quartz data fits well as a simple sum, exploiting the symmetry of the detector. The mSR remnants vanish.

  22. All 170 Detectors 85 Opposite Pairs Lifetime Opposite pairs summed Front Back “front-back folded” A small asymmetry exists front / back owing to residual longitudinal polarization 

  23. MuLan Final Errors and Numbers ppm units t(R06) = 2 196 979.9± 2.5 ± 0.9 ps t(R07) = 2 196 981.2 ± 3.7 ± 0.9 ps t(Combined) = 2 196 980.3 ± 2.2 ps (1.0 ppm) Dt(R07 – R06) = 1.3 ps New GF GF(MuLan) = 1.166 378 8(7) x 10-5 GeV-2 (0.6 ppm)

  24. Typical fit normalized residuals MuCap Negative Muon Lifetime Spectra

  25. Start- and stop-time-scans Rate versus run duration Data run number (~3 minutes per run)

  26. The disappearance rate is independent of azimuth(non trivial since TPC is asymmetric vertically owing to drift direction) Beam View of MuCap Detector Fit Rate (s-1) Azimuthal Element

  27. MuCap systematic corrections, uncertainties and final capture rate • L0(06) =455,857.3 ± 7.7 ± 5.2 s-1L0(07) = 455,853.1 ± 8.3 ± 3.9 s-1 • Apply mp atomic correction • Subtract m+ decay rate: Lm+= 455170.05 ±0.46 s-1 • 3.2% increase in the uncertainty because of ppm correction • LS(06) = 717.5 ±8.0 ±5.7 s-1 • LS(07) = 713.1 ±8.6 ± 4.5 s-1 Measured disappearance rates DLS(06 – 07) = 4.4 s-1

  28. Calibration Data (nitrogen added to production gas) Production Data Extrapolated Result Imp. Capture: m-Z  (Z-1) n n Gas impurities are monitored directly. Correction is based on measurement. Calibration done at high concentation L 0 Observed capture yield YZ 2004 run: cN < 7 ppb, cH2O~30 ppb 2006 / 2007 runs: cN < 7 ppb, cH2O~10 ppb

  29. molecular formation Atomic bound state effect External corrections to L MuCap MuLan LS(MuCap prelim.*) = 715.1 ± 5.4stat± 5.0syst s-1 * Small revision of molecular correction might affect LS < 0.5 s-1 and syst. error LS(theory) = 711.5 ± 3.5 ± 3 s-1

  30. Precise and unambiguous MuCap resultsolves longstanding puzzle gP(MuCap prelim.) = 8.0 ± 0.5 gP(theory) = 8.26 ± 0.23

  31. Compare Lifetimes !(If you believe cPT more than CPT ) tMuLan= 2 196 980.3 ± 2.2 ps Free m+ Effective* m- tMuCap= 2 196 963    +/- 42 ps Difference: • *Important assumptions • Assume cPT prediction is exact • Correct for mp atomic shift (easy) • Correct for impurity distortion (expt. errors are included)

  32. Summary • MuLan has finished and published • 1.0 ppm final error achieved, as proposed • The most precise particle or nuclear lifetime evermeasured • Most precise Fermi constant • Modest check of muonium versus free muon • MuCap has finished; publication in progress • First unambiguous determination of gP • Excellent agreement with theory • Method paves way for future MuSunexpt on md capture MuCap MuLan MuCap 2012

  33. Collaborations MuLan Boston University, USA University of Illinois at Urbana-Champaign, Urbana, USA James Madison University, Harrisonburg, USA University of Kentucky, Lexington, USAKVI, University of Groningen, Groningen, The Netherlands Paul Scherrer Institute (PSI), Villigen, Switzerland Regis University, Denver, USA University of Washington, Seattle, USA MuCap Petersburg Nuclear Physics Institute (PNPI), Gatchina, RussiaPaul Scherrer Institute (PSI), Villigen, Switzerland University of California, Berkeley (UCB and LBNL), USA University of Illinois at Urbana-Champaign, Urbana, USA University of Washington, Seattle, USA UniversitéCatholique de Louvain, BelgiumUniversity of Kentucky, Lexington, USABoston University, USA Regis University, Denver, USA

  34. Backups

More Related