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Final results from TWIST WNPPC 2010, Banff, Alberta

Final results from TWIST WNPPC 2010, Banff, Alberta. James Bueno, University of British Columbia on behalf of the TWIST collaboration. Outline. 1. Apparatus improvements Systematic uncertainties for ρ and δ Systematic uncertainties for P μ ξ Quality of data The final results

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Final results from TWIST WNPPC 2010, Banff, Alberta

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  1. Final results from TWIST WNPPC 2010, Banff, Alberta James Bueno, University of British Columbiaon behalf of the TWIST collaboration

  2. Outline 1 • Apparatus improvements • Systematic uncertainties for ρ and δ • Systematic uncertainties for Pμξ • Quality of data • The final results • Implications for the Standard Model First announcement outside of TRIUMF James Bueno, WNPPC 2010, Banff, Alberta

  3. TRIUMF Weak Interaction Symmetry Test • Highly polarised μ+ stopped in centre of symmetric detector. • e+ tracked in uniform magnetic field. • Measures muon decay parameters by comparison to a detailed GEANT3 simulation. • Final data acquired in 2006/2007. Nucl. Instr. and Meth.A548 (2005) 306-335 Jan 2010: Analysis complete James Bueno, WNPPC 2010, Banff, Alberta

  4. M13 beam line improvements 3 Nucl. Instr. and Meth.A566 (2006) 563-574 Stopping target James Bueno, WNPPC 2010, Banff, Alberta

  5. M13 beam line improvements 3 Nucl. Instr. and Meth.A566 (2006) 563-574 Stopping target Improved engineering of TECs Muons selected from different depths Beamline upgraded: “quadrupole steering” added James Bueno, WNPPC 2010, Banff, Alberta

  6. Spectrometer improvements 4 Nucl. Instr. and Meth. A548 (2005) 306-335 James Bueno, WNPPC 2010, Banff, Alberta

  7. Spectrometer improvements 4 Al and Agtargets Variable density gas degrader Voltage changed Permanent downstream trigger Chamber spacing changed Nucl. Instr. and Meth. A548 (2005) 306-335 James Bueno, WNPPC 2010, Banff, Alberta

  8. Final uncertainties for ρ and δ 5 includes uncertainty due to radiative corrections James Bueno, WNPPC 2010, Banff, Alberta

  9. Positron interactions 6 “Broken tracks”: δ-electrons: 2 x e+, 1 x e−Bremsstrahlung: 2 x e+ δ-electrons: data/sim agree < 1% Brem: data/sim differ by ≈2.4% James Bueno, WNPPC 2010, Banff, Alberta

  10. Momentum calibration 7 Spectrum endpoint provides a calibration Simulation anddata pmax differ by≈10 keV/c Difference must be propagated to rest of spectrum James Bueno, WNPPC 2010, Banff, Alberta

  11. Momentum calibration 8 Extremes are application as a shift and scale Scale Shift Difference between these choices gives uncertainties of1.0 x 10-4 for ρ, and 1.1 x 10-4 for δ. James Bueno, WNPPC 2010, Banff, Alberta

  12. Chamber response 9 • Space-time relationship from GARFIELD is now refined to minimise track fit residuals. • Corrects for plane-to-plane construction differences, tracking bias. e+ (paper describing technique is submitted toNucl. Instr. and Meth. A) James Bueno, WNPPC 2010, Banff, Alberta

  13. Uncertainties for Pμξ 10 James Bueno, WNPPC 2010, Banff, Alberta

  14. Uncertainties for Pμξ 10 James Bueno, WNPPC 2010, Banff, Alberta

  15. Muon beam and fringe field 11 2 m James Bueno, WNPPC 2010, Banff, Alberta

  16. Muon beam and fringe field 11 Position Angle 2 m James Bueno, WNPPC 2010, Banff, Alberta

  17. Muon beam and fringe field 12 Transverse magnetic field components Units mT At target, Pμ=0.9975 ± ? James Bueno, WNPPC 2010, Banff, Alberta

  18. Muon beam and fringe field 13 How accurately do we know the beam polarisation at target entry? Polarisation uncertainty (units 10−4) James Bueno, WNPPC 2010, Banff, Alberta

  19. Muon beam / field alignment 14 new old Beam steered onto symmetry axis. Pμ now less sensitive to alignment uncertainties. y (cm) Pμ uncertain at level of + 1.2 − 6.4 x 10−4 James Bueno, WNPPC 2010, Banff, Alberta

  20. Magnetic field components 15 Indirect validation: polarisation of real beam lowered. How well does the simulation reproduce the changes? Example: angle θy ~ 28 mrad introduced Polarisation decrease of (105 ± 9) x 10-4 Comparison I y vs. z Comparison II: position off axis by ~1 cm,angle θx ~ 10 mrad introduced. Comparison III: TECs-in through entire set, increasing multiple scattering upstream of fringe field. Small transverse field components need increasing by 10% to improve data and simulation agreement. James Bueno, WNPPC 2010, Banff, Alberta

  21. Selecting muons in metal target 16 wires foil Muon last hit must be in PC6, with no signal in PC7. PC5 PC6 PC7 (PC = proportional chamber) James Bueno, WNPPC 2010, Banff, Alberta

  22. Selecting muons in metal target 16 stops in gas wires foil PC6 signal amplitude PC5 signal amplitude Cut placed so that < 0.5%of the gas distribution contaminates “zone 1”. PC5 PC6 (PC = proportional chamber) James Bueno, WNPPC 2010, Banff, Alberta

  23. Measuring depolarisation in target 17 Targets are high purity (>99.999% purity) Al and Ag. Subsidiary μ+SRexperiment: λ (ms−1) no “fast depolarisation” down to 5 ns Al Ag James Bueno, WNPPC 2010, Banff, Alberta

  24. Outline 1 • Apparatus improvements • Systematic uncertainties for ρ and δ • Systematic uncertainties for Pμξ • Quality of data • The final results • Implications for the Standard Model First announcement outside of TRIUMF James Bueno, WNPPC 2010, Banff, Alberta

  25. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 All sets are used James Bueno, WNPPC 2010, Banff, Alberta

  26. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 Nominal sets James Bueno, WNPPC 2010, Banff, Alberta

  27. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 Stopping distribution changed James Bueno, WNPPC 2010, Banff, Alberta

  28. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 Magnetic field changed James Bueno, WNPPC 2010, Banff, Alberta

  29. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 Muon beam steered off-axis James Bueno, WNPPC 2010, Banff, Alberta

  30. Set-to-set consistency: ρ and δ 18 (difference between data and hidden values) Ag Al units 10−4 Lower muonmomentum James Bueno, WNPPC 2010, Banff, Alberta

  31. Set-to-set consistency: Pμξ 19 (difference between data and hidden values) Ag Al TECs-in units 10−4 Magnetic field changed Muon beam steered (indicated sets were not included for Pμξ) James Bueno, WNPPC 2010, Banff, Alberta

  32. Spectrum fit quality 20 Excellent fit quality over kinematic fiducial James Bueno, WNPPC 2010, Banff, Alberta

  33. Before unblinding 21 Collaboration agreed on: • Data sets to include. • Systematic uncertainties and corrections. • Level of required consistency with previous results. • Do we combine new results with intermediate TWIST measurements? (new results supersede) • Course of action if results are inconsistent with the Standard Model. (we publish!) James Bueno, WNPPC 2010, Banff, Alberta

  34. Results revealed (29 Jan 2010) 22 ρ = 0.74991 ± 0.00009 (stat) ± 0.00028 (syst) δ = 0.75072 ± 0.00016 (stat) ± 0.00029 (syst) James Bueno, WNPPC 2010, Banff, Alberta

  35. Results revealed (29 Jan 2010) 23 Pμξ = 1.00084 ± 0.00035 (stat) + 0.00165 (syst) − 0.00063 (syst) Pre-TWIST: 0.9975 ≤ Pμδ/ρ (90% C.L.) Pμξδ / ρ =1.00192 + 0.00167 − 0.00066 2.9 σ from SM, under investigation James Bueno, WNPPC 2010, Banff, Alberta

  36. Left-right symmetric models 24 Phys. Rev. D 34, 3449 - 3456 (1986) • Models add a right-handed current (V+A) to the weak interaction. • Right-handed W-boson introduced at higher energies. • Mass of WR > Mass of WL. Weak interaction eigenstates (WL, WR) in terms of mass eigenstates (W1,W2) and mixing angle (ζ): WL = W1 cos ζ + W2 sin ζ WR = eiω ( −W1 sin ζ + W2cos ζ) Muon polarisation and decay parameters ξ and ρ are sensitive to m2 (the new boson’s mass)and ζ (the mixing angle). James Bueno, WNPPC 2010, Banff, Alberta

  37. Left-right symmetric models 25 Phys. Rev. D 34, 3449 - 3456 (1986) 90% C.L. exclusion 90% C.L. exclusion Generalised LRS Manifest LRS Allowed Allowed D0 direct searchPhys. Rev. Lett. 100, 031804 (2008) James Bueno, WNPPC 2010, Banff, Alberta

  38. Global analysis of muon decay data 26 Method described in Phys. Rev. D, 72:073002 (2005) General 4-fermion interaction: Standard Model (“V-A”): (all others zero) Global analysis determines weak coupling constants using: • TWIST results: ρ, δ, Pμξ • Polarisation of e+ (longitudinal and transverse) • Radiative muon decay James Bueno, WNPPC 2010, Banff, Alberta

  39. Global analysis of muon decay data 27 • New limit on right-handed muon couplings: Pre-TWIST: QμR < 5.1 x 10−3 (90% C.L.)New result: QμR < 5.8 x 10−4 (90% C.L.) • Uncertainty for η reduced: 2005 global analysis: η = − 0.0036 ± 0.0069 New result: η = − 0.0033 ± 0.0046 • Improved uncertainties for other coupling constants: Coupling Pre-TWIST New | gSRR| < 0.066 < 0.031 | gVRR| < 0.033 < 0.015 | gSLR| < 0.125 < 0.041 | gVLR| < 0.060 < 0.018 | gTLR| < 0.036 < 0.012 Preliminary James Bueno, WNPPC 2010, Banff, Alberta

  40. Summary 28 • Systematic uncertainties in muon decay parameter measurements were substantially reduced in TWIST. • Total uncertainties were reduced by factors of8.7, 11.6, and 7.0 for ρ, δ and Pμξ respectively, roughly achieving the goals of the experiment. • Differences with Standard Model predictions are respectively −0.3 σ, +2.2 σ, and +1.2 σ. • We cannot yet explain the more significant deviation of Pμξ δ/ρ above the limit of 1.0. James Bueno, WNPPC 2010, Banff, Alberta

  41. The TWIST collaboration (http://twist.triumf.ca) Supported by NSERC, the National Research Council of Canada, the Russian Ministry of Science, and the US department of energy. Computing resources provided by WestGrid. James Bueno, WNPPC 2010, Banff, Alberta

  42. Backup slides James Bueno, WNPPC 2010, Banff, Alberta

  43. Magnetic field components 14 Comparison I Nominal field James Bueno, WNPPC 2010, Banff, Alberta

  44. Magnetic field components 14 Comparison I Scaling applied to Bx and By components of field map Nominal field James Bueno, WNPPC 2010, Banff, Alberta

  45. Magnetic field components Small transverse magnetic field components are scaled. Estimate of error Data and simulation agree best when components are increased by 10%. James Bueno, WNPPC 2010, Banff, Alberta

  46. Coupling constants and decay parameters The muon decay parameters are bilinear combinations of the coupling constants: James Bueno, WNPPC 2010, Banff, Alberta

  47. Summary of improvements James Bueno, WNPPC 2010, Banff, Alberta

  48. Decay spectrum When e+ polarization not detected, spectrum is described by four muon decay parameters (bilinear combinations of ‘s) James Bueno, WNPPC 2010, Banff, Alberta

  49. Blind analysis • Data compared to GEANT3 simulation with hidden decay parameters. • Spectrum is linear inPμξ, Pμξδ, ρ, η • Differences from hidden parameters are measured. • Hidden parameters are revealed after systematic uncertainties evaluated. James Bueno, WNPPC 2010, Banff, Alberta

  50. Hidden value tolerances data minus simulation hidden value in simulation ρ result (data) δ result Pμξ result James Bueno, WNPPC 2010, Banff, Alberta

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