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From Z 0 to Zero: A Precise Measurement of the Weak Mixing Angle from SLAC E158

Discover the historical journey, motivation, and new results of the SLAC E158 experiment led by Yury Kolomensky at UC Berkeley. Explore the experimental technique and the high-energy physics data collected, providing insights into electroweak interactions and beyond. The collaboration, challenges, and future outlook are highlighted.

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From Z 0 to Zero: A Precise Measurement of the Weak Mixing Angle from SLAC E158

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  1. From Z0 to Zero:A Precise Measurement of the Weak Mixing Angle from SLAC E158 Yury Kolomensky UC Berkeley For SLAC E158 Collaboration

  2. Outline • Historical interlude • SLAC E158 • Motivation • Experimental technique • New results • Outlook Yury Kolomensky, E158 Results

  3. End Station A End Station A Yury Kolomensky, E158 Results

  4. End Station A: How It All Started SLAC-R-090 (08/1968) Experiment E-4: SLAC-MIT-CIT (precursor to discovery of quarks) First high-power LH2 target at SLAC ! Yury Kolomensky, E158 Results

  5. SLAC E122 Yury Kolomensky, E158 Results

  6. SLAC E122 Detector e 16 – 22 GeV Liquid Deuterium Polarized GaAs source High current 30 cm target Dedicated run Yury Kolomensky, E158 Results

  7. E122 Asymmetry Yury Kolomensky, E158 Results

  8. SLAC E122 Result (1978) sin2qW = 0.224 + 0.020 First definitive measurement of mixing between the weak and electromagnetic interaction Yury Kolomensky, E158 Results

  9. A-Line 50 GeV Upgrade 50 GeVcapability In ESA: 1995 Polarized structure Function experiments: E154,E155,E155x Yury Kolomensky, E158 Results

  10. E158 Heritage • SLAC provides unique capabilities with high-intensity, high-energy, high-polarization beams • We are building on the past experience and physics interests • Electroweak physics • Even tests of QED and QCD predictions (somewhat surprisingly) • 3 fundamental interactions for the price of one experiment !  Yury Kolomensky, E158 Results

  11. SLAC E158: Motivation Yury Kolomensky, E158 Results

  12. “High Energy”ElectroweakData (LEP EWWG) Yury Kolomensky, E158 Results

  13. “High Energy” EW Data • Spectacular precision • Quantum loop level (LO to NNLO) • Precise indirect constraints on top and Higgs masses • General consistency with the Standard Model • Few smoking guns • Leptonic and hadronic Z couplings seem inconsistent ? • Direct searches have not yielded new physics phenomena (so far) • Complementary sensitivity at low energies • Rare or forbidden processes • Symmetry violations • Precision measurements BaBar and E158 Yury Kolomensky, E158 Results

  14. Direct vs Indirect Searches (according to Grimm Brothers) Yury Kolomensky, E158 Results

  15. Electroweak Physics Away from Z pole • Precision Z observables establish anchor points for SM • Low energy observables probe interference between SM and NP • Current “low energy” experiments are accessing scales of beyond 10 TeV Yury Kolomensky, E158 Results

  16. Electroweak Mixing Angle • Mixing of neutral SU(2)U(1) currents: • Mixing angle: • e = g sinqW = g’cosqW • At tree level sin2qW = 1-MW2/MZ2 Yury Kolomensky, E158 Results

  17. Running of Weak Mixing Angle sin2qW = e2/g2 → test gauge structure of SU(2)U(1) 3% Yury Kolomensky, E158 Results

  18. Status Before E158 (1997) sin2qW Q (GeV) Yury Kolomensky, E158 Results

  19. Status A Week Ago sin2qw Run I & II Q (GeV) Yury Kolomensky, E158 Results

  20. The Experiment Yury Kolomensky, E158 Results

  21. Weak-Electromagnetic Interference in Electron Scattering Yury Kolomensky, E158 Results

  22. Fixed Target Møller Scattering Purely leptonic reaction gee ~ 1 – 4 sin2W Yury Kolomensky, E158 Results

  23. Parity Violation in Møller Scattering • Scatter polarized 50 GeV electrons off unpolarized atomic electrons • Measure • Small tree-level asymmetry • At tree level, • Raw asymmetry about 130 ppb • Measure it with precision of 10% • Most precise measurement of sin2qW at low Q2 Yury Kolomensky, E158 Results

  24. LEPII e e e e e e e e E158 R R R R L L L L + – L~15 TeV e e e e e e e e Compositeness e e q l+ Z’ FNAL Z´ q e e l- Neutral currents (GUTs, extra dims) MZ’~1 TeV e e D- - e e Scalar interactions (LFV) E158: Physics Sensitivity • Unique window of opportunity • Complementary to collider searches Yury Kolomensky, E158 Results

  25. PAC approval Polarized Beam Instrumentation R&D Spectrometer and Detector Design Construction Funds and Test Beams Commissioning Run Physics Run I Physics Run II Physics Run III (final statistics) Sept 1997: 1998: 1999: 2000: 2001: Spring 2002: Fall 2002: Summer 2003: E158 Collaboration Institutions Caltech Syracuse Princeton Jefferson Lab SLAC UC Berkeley CEA Saclay UMass Amherst Smith College U. of Virginia 60 physicists, 7 Ph.D. students Chronology: Yury Kolomensky, E158 Results

  26. Run I Results Published Yury Kolomensky, E158 Results

  27. Experimental Technique • Scattering of polarized electrons off atomic electrons • High cross section (14 mBarn) • High intensity electron beam, ~80% polarization • 1.5m LH2 target • Luminosity 4*1038 cm-2s-1 • High counting rates [ flux-integrating calorimeter • Principal backgrounds: elastic and inelastic ep • Main systematics: beam polarization, helicity-correlated beam effects, backgrounds Yury Kolomensky, E158 Results

  28. Major Challenges • Statistics ! • Need to accumulate ~1016 electrons • Suppress other sources of noise to be dominated by counting statistics • Beam monitoring and resolution • Major (potential) source of additional jitter • Beam systematics • False asymmetries • Backgrounds • Need to measure insitu Yury Kolomensky, E158 Results

  29. Key Ingredients • High beam polarization and current • Largest high-power LH2 target in the world • Spectrometer optimized for Møller kinematics • Stringent control of helicity-dependent systematics. Passive asymmetry reversals Yury Kolomensky, E158 Results

  30. Correct for difference in R/L beam properties: charge, position, angle, energy R-L differences coefficients determined experimentally Physics asymmetry: backgrounds beam polarization Parity-Violating Asymmetry Rapidly flip electron helicity (120 Hz) and form pulse pairs of opposite helicity Measure pulse-pair flux asymmetry: Yury Kolomensky, E158 Results

  31. Statistics # electrons per pulse 107 Rep rate (120 Hz) 109 Seconds/day 1014 100 days 1016 DA ~ 10-8 Yury Kolomensky, E158 Results

  32. E158 Runs Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003 Yury Kolomensky, E158 Results

  33. Eliminating Beam Jitter Integrate Detector response: Flux Counting Yury Kolomensky, E158 Results

  34. New cathode Electrons per pulse Old cathode Laser Power (µJ) Polarized Beam High doping for 10-nm GaAs surface overcomes charge limit. Low doping for most of active layer yields high polarization. No sign of charge limit! Yury Kolomensky, E158 Results

  35. Control of Beam Systematics • Beam helicity is chosen pseudo- randomly at 120 Hz • use electro-optical Pockels cell in Polarized Light Source • sequence of pulse quadruplets • Reduce beam asymmetries by feedback at the Source • Control charge asymmetry and position asymmetry Yury Kolomensky, E158 Results

  36. Passive Reversals and Checks • Physics Asymmetry Reversals: • Insertable Half-Wave Plate in Polarized Light Source • (g-2) spin precession in A-line (45 GeV and 48 GeV data) • False Asymmetry Reversals: • Reverse false beam position and angle asymmetries; physics asymmetry unchanged • Insertable “-I/+I” Inverter in Polarized Light Source • “Null Asymmetry” Cross-check is provided by a Luminosity Monitor • measure very forward angle e-p (Mott) and Møller scattering Yury Kolomensky, E158 Results

  37. Polarized Source Yury Kolomensky, E158 Results

  38. RF Cavity BPM Pulse-to-pulse monitoring of beam asymmetries and resolutions: toroid 30 ppm energy 1 MeV BPM 2 microns Agreement (MeV) BPM24 X (MeV) Resolution 1.05 MeV BPM12 X (MeV) Beam Diagnostics Energy dithering region A-Line linac Yury Kolomensky, E158 Results

  39. Charge asymmetry agreement at 45 GeV Charge asymmetry at 1 GeV Energy difference agreement in A line Energy difference in A line Position agreement ~ 1 nm Position differences < 20 nm Beam Asymmetries Yury Kolomensky, E158 Results

  40. Møller Polarimetry • Average polarization: • 85 ± 5% in Run I • 84 ± 5% in Run II • 91 ± 5% in Run III • New superlattice ! Yury Kolomensky, E158 Results

  41. Liquid Hydrogen Target Refrigeration Capacity 1 kW Operating Temperature 20 K Length 1.5 m Flow Rate 5 m/s Vertical Motion 6 inches Yury Kolomensky, E158 Results

  42. Kinematics Yury Kolomensky, E158 Results

  43. Spectrometer x (cm) Yury Kolomensky, E158 Results

  44. target Detector cart Concrete shielding Spectrometer magnets Setup in ESA Yury Kolomensky, E158 Results

  45. Yury Kolomensky, E158 Results

  46. Detector Concept Yury Kolomensky, E158 Results

  47. Yury Kolomensky, E158 Results

  48. Basic Idea: light guide :quartz : copper air shielding PMT MOLLER Detector electron flux Yury Kolomensky, E158 Results

  49. Luminosity Monitor more than 108 scattered electrons per spill at lab ~ 1 mrad • Null asymmetry test • Density fluctuations monitor • Enhanced sensitivity • to beam fluctuations Parallel plates Yury Kolomensky, E158 Results

  50. Profile Detector • 4 Quartz Cherenkov detectors with PMT readout • insertable pre-radiators • insertable shutter in front of PMTs • Radial and azimuthal scans • collimator alignment, spectrometer tuning • background determination • Q2 measurement Yury Kolomensky, E158 Results

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