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Parity Violation in Electron Scattering

Parity Violation in Electron Scattering. * SLAC E122. * SLAC E158. * FUTURE. Emlyn Hughes SLAC DOE Review June 2, 2004. Polarized Electron Scattering. e-. e-. e-. e-. g. Z. unpolarized quarks or electrons or protons. Parity conserving. Parity violating. Electroweak Mixing Angle.

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Parity Violation in Electron Scattering

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  1. Parity Violation in Electron Scattering * SLAC E122 * SLAC E158 * FUTURE Emlyn Hughes SLAC DOE Review June 2, 2004

  2. Polarized Electron Scattering e- e- e- e- g Z unpolarized quarks or electrons or protons Parity conserving Parity violating

  3. Electroweak Mixing Angle e = g sinqw Characterizes the mixing between the weak and EM interaction in the electroweak theory 2 Mw 2 sin2qw = 1 - Mz

  4. SLAC Parity Experiments Detector e- Target High Energy (unpolarized) R L s - s APV = Parity-violating asymmetry R L s + s

  5. End Station A End Station A

  6. SLAC E122

  7. SLAC E122 Detector e 16 – 22 GeV Liquid Deuterium GaAs source High current 30 cm target Dedicated run

  8. 120 Hz Reversed every few runs

  9. SLAC E122 waveplate reversal

  10. SLAC E122 waveplate reversal Parity-violating asymmetry

  11. SLAC E122 Energy Scan Parity-violating asymmetry

  12. SLAC E122 Result (1978) sin2qw = 0.224 + 0.020 First definitive measurement of mixing between the weak and electromagnetic interaction

  13. Atomic Parity Violation Bismuth

  14. Atomic Parity Violation Bismuth

  15. Atomic Parity Violation Bismuth

  16. Atomic Parity Violation Bismuth E122

  17. TODAY... LEP and SLC e+e- collider Dsin2qw = 0.00017 (PDG2002) from Z pole measurements

  18. Status in 1999 sin2qw ~5% Q (GeV)

  19. SLAC Experiment E158 Detector e 50 GeV Liquid Hydrogen e-e- scattering s - s APV = s + s Without electroweak radiative corrections, 2 m E GF 16 sin q 1 ( ) - sin2qw APV = 2 4 2p  (3 + cos q)2 In practice: APV ~ 1.5 x 10-7

  20. E158 Collaboration • SLAC • Smith College • Syracuse • UMass • Virginia • UC Berkeley • Caltech • Jefferson Lab • Princeton • Saclay 7 Ph.D. Students 60 physicists Sept 97: EPAC approval 1998-99: Design and Beam Tests 2000: Funding and construction 2001: Engineering run 2002: Physics Runs 1 (Spring), 2 (Fall) 2003: Physics Run 3 (Summer)

  21. Challenges I. Statistics II. Beam monitoring & resolution  jitter vs. statistics III. Beam systematics  false asymmetries IV. Backgrounds

  22. target Detector cart Concrete shielding Spectrometer magnets Setup in End Station A

  23. STATISTICS # electrons per pulse 107 Rep rate (120 Hz) 109 Seconds/day 1014 100 days 1016 DA ~ 10-8

  24. II. BEAM MONITORING

  25. toroid 30 ppm energy 1 MeV BPM 2 microns Agreement (MeV) BPM24 X (MeV) Resolution 1.05 MeV BPM12 X (MeV) Beam Monitoring Correlations

  26. III. Beam Asymmetries Polarized source

  27. SLOW REVERSALS * Halfwaveplate @ source ~few hours * 48 vs. 45 GeV energy ~ few days

  28. APV vs. time ppb

  29. IV. BACKGROUNDS * electron-proton elastic scattering * pion production * radiative inelastic electron-proton scattering W2 > 3 GeV2 * 2 photon events with transverse polarization * * *

  30. ep Detector Asymmetry

  31. Transversely Polarized Beam

  32. E158 Physics Runs Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003

  33. Run I & II

  34. Run I

  35. RUNI FINAL RESULT At Q2 = 0.027 (GeV/c)2…. APV= -175  30 (stat)  20 (syst) ppb MS sin2  = 0.2293 ± 0.0024 (stat) ±0.0016 (syst) w MS Theory: sin2  = 0.2311 ± 0.00016 w

  36. RUNI & II PRELIMINARY At Q2 = 0.027 (GeV/c)2…. APV= -160  21 (stat)  17 (syst) ppb MS sin2  = 0.2308 ± 0.0015 (stat) ±0.0014 (syst) w MS Theory: sin2  = 0.2311 ± 0.00016 w

  37. Status in 1999 sin2qw Q (GeV)

  38. Cesium Atomic Parity Violation Result vs. Time (Colorado measurement) sin2qw 0.240 Standard Model 0.238 Kuchiev Flambaum 0.236 Kozlov Porsev Tupitsyn Johnson Bednyhakov Soff 0.234 Derevianko Bennett Wieman Dzuba Flambaum 0.232 Wieman et al. 0.230 2000 1999 1998 2001 2002 2003 1997 Modifications in the theoretical corrections to the atomic structure

  39. Status today sin2qw Run I & II Q (GeV)

  40. Including E158 projections... Run I & II sin2qw E158 Projected Error bar Q (GeV)

  41. Beyond Standard Model Implications... * Limit on LLL ~ 7 TeV * Limit on Z ~ 400 GeV • * Limit on lepton flavor violating coupling ~ 0.02GF  Limits will improve with new data

  42. Future Measurements

  43. LHC Not a parity experiment …  Has major impact on precision low energy tests for discovery potential Z’, supersymmetry, compositeness, leptoquarks, etc… in the TeV range

  44. SUMMARY * Performed a first measurement of parity violation in e-e- scattering Final results in ~ 1/2 year * Future parity experiments active * Complementary to collider experiments

  45. Run I Systematics

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