Low Energy Tests of the Standard Model

1. Low Energy Tests of the Standard Model * PAST * PRESENT * FUTURE Emlyn Hughes Spin 2004 Trieste October 14, 2004

2. 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

3. 3 Types of Measurements * Electron scattering (parity violation) * Atomic parity violation * Neutrino physics (NC/CC cross section)

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

5. Parity Violation in the Electroweak Theory R L s - s APV = R L s + s g2 2 + q2 AW mZ 2AW AEM PV 2 ~ 2 ~ ~ A AEM 2 2 + e2 AW AEM q2 PV q2 A ~ 2 2 mZ

6. SLAC

7. End Station A End Station A

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

9. SLAC E80

10. Yale E80 Polarized Source

11. SLAC End Station A

12. SLAC E95

13. Results on Parity Violation E80 ALR < 5 x 10-3at Q2 ~ 1.4, 2.7 GeV2 E95 ALR < 3.2 x 10-3at Q2 ~ 4 GeV2 Not sensitive to electroweak mixing in the Standard Model

14. First Measurements of Electroweak Mixing

15. SLAC E122

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

17. 120 Hz Reversed every few runs

18. SLAC E122 waveplate reversal

19. SLAC E122 waveplate reversal Parity-violating asymmetry

20. SLAC E122 Energy Scan Parity-violating asymmetry

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

22. Atomic Parity Violation e- e- g or Z p 2 2 mea LR q2 -14 A ~ 2 ~ 2 10 ~ 2 2 mZ mZ

23. Experiment Z3 Law Heavy Atoms Theory PV Signal sin2qw Bismuth Z = 83

24. Atomic Parity Violation Bismuth

25. Atomic Parity Violation Bismuth

26. Atomic Parity Violation Bismuth

27. Atomic Parity Violation Bismuth E122

28. Neutrino Physics Bubble Chamber Gargamelle

29. HPWF Neutrino Detector (Harvard, Pennsylvania, Wisconsin, Fermilab)

30. 1974

32. 1978

33. (1977) (1977) (1975) (1977) 1978

34. TODAY... LEP and SLC e+e- collider Dsin2qw = 0.00016 (PDG2004) from Z pole measurements

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

36. 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

37. 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)

38. Scattering Processes e- e- e- e- g Z e- e- e- e- Parity-conserving Parity-violating e- e- g g Background p p

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

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

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

44. II. BEAM MONITORING

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

47. III. Beam Asymmetries Polarized source

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

49. APV vs. time ppb

50. Asymmetry Results