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Parity Nonconservation in Møller Scattering

Parity Nonconservation in Møller Scattering. E158: A Precision Measurement of the Weak Mixing Angle in Fixed Target electron-electron (Møller) Scattering (The structure of the virtual Z in dense electronic matter) Krishna Kumar University of Massachusetts, Amherst DIS05, April 29, 2005.

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Parity Nonconservation in Møller Scattering

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  1. Parity Nonconservation in Møller Scattering E158: A Precision Measurement of the Weak Mixing Angle in Fixed Target electron-electron (Møller) Scattering (The structure of the virtual Z in dense electronic matter) Krishna Kumar University of Massachusetts, Amherst DIS05, April 29, 2005 Parity Nonconservation in Møller Scattering

  2. Outline • Physics Motivation • Experimental Overview • Final Results • Physics Implications • Outlook Parity Nonconservation in Møller Scattering

  3. Beyond the Standard Model • High Energy Colliders • Rare or Forbidden Processes • Symmetry Violations • Electroweak One-Loop Effects Complementary Approaches • Precise predictions at level of 0.1% • Indirect access to TeV scale physics • World electroweak data has marginal 2 • Leptonic and hadronic Z couplings barely consistent • Perhaps there are deviations lurking elsewhere? Parity Nonconservation in Møller Scattering

  4. Electroweak Physics at Low Q2 Logical to push to higher energies, away from the Z resonance LEPII, Tevatron, LHC access scales greater than L ~ 10 TeV Complementary: Parity Violating vs Parity Conserving Q2 << scale of EW symmetry breaking Parity Nonconservation in Møller Scattering

  5. Weak Neutral Current at low Q2 Purely leptonic reaction QeW ~ 1 - 4sin2W Z0 Fixed Target Møller Scattering Parity Nonconservation in Møller Scattering

  6. Weak-Electromagnetic Interference Zel’dovich ‘59 Parity Nonconservation in Møller Scattering

  7. E158 at SLAC A Precision Measurement of sin2W at low Q2 Highest electron beam energy with longitudinal beam polarization: SLAC Raw asymmetry ~ 130 ppb Q2 = mE = 0.025 GeV2 Count at ~ 1 GHz Need 1016events (APV) ~ 10 ppb • 1997: EPAC approval • 2000: Construction • 2002-2003: Data collection • 2004: First publication • UC Berkeley • Caltech • Jefferson Lab • Princeton • Saclay • SLAC • Smith College • Syracuse • UMass • Virginia 7 Ph.D. Students 60 physicists Parity Nonconservation in Møller Scattering

  8. E158 New Physics Reach Parity Nonconservation in Møller Scattering

  9. Stanford Linear Accelerator Center Parity Nonconservation in Møller Scattering

  10. Kinematics Parity Nonconservation in Møller Scattering

  11. Experimental Apparatus target Detector cart Concrete shielding Spectrometer magnets 60 meter 3 Physics Runs in 2002 and 2003 • Longitudinally Polarized Beam • Precision Beam Monitoring • Liquid Hydrogen Target • Spectrometer • Detectors Major innovations in each subsystem Parity Nonconservation in Møller Scattering

  12. E158 Spectrometer Parity Nonconservation in Møller Scattering

  13. Optical Pumping Modulate longitudinal polarization of the electron beam • Beam helicity is chosen pseudo-randomly at 120 Hz • sequence of pulse quadruplets • Data analyzed as “pulse-pairs” Parity Nonconservation in Møller Scattering

  14. Experimental Technique Parity Nonconservation in Møller Scattering

  15. E158 Analysis Basic Idea: light guide :quartz : copper air shielding PMT electron flux Radial and azimuthal segmentation • Corrections for beam fluctuations • Average over runs • Statistical tests • Beam polarization and other normalization Parity Nonconservation in Møller Scattering

  16. Final Analysis of All 3 Runs • APV = • (-131 ± 14 ± 10) x 10-9 g-2 spin precession 45 GeV: 14.0 revs 48 GeV: 14.5 revs Parity Nonconservation in Møller Scattering

  17. Electroweak Physics sin2qW = e2/g2 test gauge structure of SU(2)U(1) 3% Parity Nonconservation in Møller Scattering

  18. Final Physics Results 6s sin2WMS(MZ) sin2eff = 0.2397 ± 0.0010 ± 0.0008 (95% confidence level) * Limit on LLL ~ 7 or 16 TeV hep-ex/0504049 submitted Tuesday! * Limit on SO(10) Z’ ~ 1.0 TeV • * Limit on lepton flavor violating coupling ~ 0.01GF Parity Nonconservation in Møller Scattering

  19. Future Measurements Semi-Leptonic: Is NuTeV new EW or QCD physics? PV Elastic electron-proton scattering at JLab: (sin2w)=0.0007 PV Deep Inelastic Scattering at upgraded JLab • Unique, complementary probes of New Physics • Theoretical issues are interesting in themselves: Unique, outstanding opportunity for a dedicated apparatus with JLab upgrade Leptonic: Ultimately the “best” EW precision measurements -e scattering in reactor: at best can do (sin2w)=0.002 Møller scattering at upgraded JLab: (sin2w)=0.0003! • Comparable to single LEP measurements: shed light on disagreement • Best low energy measurement until ILC or -Factory • Could be done ~ 2012 Parity Nonconservation in Møller Scattering

  20. Ultrahigh Precision Measure contribution from scalars to oblique corrections t new H physics b Z (world average ~0.00016) Critical crosscheck Compare with masses of “bumps” at new colliders: ALR and MW at future colliders: K.K, Snowmass 96 Systematics extremely challenging! Energy scale to 10-4, polarimetry to 0.15% Møller scattering at the ILC • Fixed target has advantages for systematics • Could work with ILC “exhaust”beam Parity Nonconservation in Møller Scattering

  21. Conclusions • SLAC E158 data taking phase has been completed • Physics results: • Parity is violated in Møller scattering • Final result with all data: APV: -131 ± 14 ± 10 ppb • Running of weak mixing angle established at 6 • sin2eff = 0.2397 ± 0.0010 ± 0.0008 • New constraints on TeV scale physics • Inelastic e-p asymmetry at low Q2 consistent with quark picture • First measurement of e-e transverse asymmetry analyzing power • This experiment could not be done elsewhere in the world • Last Fixed Target Experiment at Historic SLAC End Station A! • Final publication just submitted: hep-ex/0504049 • Future experiments could improve sensitivity by ~ 2 to 6 • An “ultimate” measurement could be done at an LC or neutrino factory Parity Nonconservation in Møller Scattering

  22. Liquid Hydrogen Target Refrigeration Capacity 1 kW Operating Temperature 20 K Length 1.5 m Flow Rate 5 m/s Vertical Motion 6 inches Parity Nonconservation in Møller Scattering

  23. Detector Concept Parity Nonconservation in Møller Scattering

  24. Detector Cart Profile Detector wheel PMT Lead Holder/shield Luminosity Monitor region • Cu-fused silica sandwich • 20 million 17 GeV electrons at 120 Hz • 100 MRad radiation dose Parity Nonconservation in Møller Scattering

  25. Parity Nonconservation in Møller Scattering

  26. Scattered Flux Profile Annulus Cerenkov detector Linear drive Bearing wheels • Scattered flux profile at all Ø • Fast measurement at nominal run conditions • 10x10 mm2 spatial resolution • Insensitive to backgrounds • Out of the way during production running • Radiation hard Parity Nonconservation in Møller Scattering

  27. Polarized Photocathode New cathode Electrons per pulse Old cathode Laser Power (µJ) 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! Parity Nonconservation in Møller Scattering

  28. Systematic Control (II) Parity Nonconservation in Møller Scattering

  29. Beam Monitoring Pulse by pulse monitoring at 1 GeV and 45 GeV energy 1 MeV BPM 2 microns toroid 30 ppm Agreement (MeV) Resolution 1.05 MeV Parity Nonconservation in Møller Scattering

  30. Physics Runs APV Sign Flips Run 1: Apr 23 12:00 – May 28 00:00, 2002 Run 2: Oct 10 08:00 – Nov 13 16:00, 2002 Run 3: July 10 08:00 - Sep 10 08:00, 2003 Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003 g-2 spin precession 45 GeV: 14.0 revs 48 GeV: 14.5 revs 1020Electrons on Target Data divided into 75 “slugs”: - Wave plate flipped ~ few hours - Beam energy changed ~ few days Parity Nonconservation in Møller Scattering

  31. Systematic Control (III) Source Laser Room CID Gun Vault Parity Nonconservation in Møller Scattering

  32. Beam Asymmetries 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 Parity Nonconservation in Møller Scattering

  33. Raw Asymmetry Statistics i ≈ 200 ppm i ≈ 600 ppb N = 818 N = 85 Million Parity Nonconservation in Møller Scattering

  34. Backgrounds & Normalization Integrating calorimeter: background dilutions and asymmetries must be separately measured or bounded. • Elastic and inelastic e-p scattering and radiative tail • High energy pions • High and low energy photons • Neutrons • Synchrotron radiation Total dilution: 9.3% in Run I, 7.6% in Run II & III • Beam polarization measured using polarized foil target • - Same spectrometer used with dedicated movable detector • Energy scale and spectrometer alignment to determine <Q2> • Linearity of PMTs • Largest systematic errors: • Inelastic ep: -22  4 ppb • Beam polarization: 0.89 ± 0.04 Parity Nonconservation in Møller Scattering

  35. Summary of Corrections • Scale factors: • Average Polarization 89 ± 4%  New “NLC” cathode ! • Linearity 99 ± 1% • Radiative corrections: 1.01 ± 0.01 Parity Nonconservation in Møller Scattering

  36. “ep” Detector Data • Radiative tail of elastic ep scattering is dominant background • 8% under Moller peak • Additional 1% from inelastic e-p scattering • Coupling is large: similar to 3 incoherent quarks: 0.8 x 10-4 x Q2 • Background reduced in Run II & III with additional collimation Parity Nonconservation in Møller Scattering

  37. Transverse Asymmetry Observe ~ 2.5 ppm up-down asymmetry w/ horizontal polarization First measurement of single-spin transverse asymmetry in e-e scattering. Asymmetry vs  Ebeam 46 GeV Two-photon exchange QED effect Flips sign at 43 GeV  for Møller scattering at 46 GeV = -3.5 ppm• sin f Theory References: 1. A. O. Barut and C. Fronsdal, (1960) 2. L. L. DeRaad, Jr. and Y. J. Ng (1975) 3. Lance Dixon and Marc Schreiber (2004) Parity Nonconservation in Møller Scattering

  38. SUSY and QeW, QpW SUSY effects in “oblique” corrections highly suppressed: No “electroweak nondecoupling” SUSY provides a potential dark matter candidate • Stable, lightest SUSY particle if baryon (B) and lepton (L) numbers are conserved Kurylov, Ramsey-Musolf, Su SUSY loops  SUSY dark matter • However, B and L need not be conserved in SUSY, leading to neutralino decay (RPV) E158 &Q-Weak QeW and QpW would have new contributions from RPV RPV 95% CL Parity Nonconservation in Møller Scattering

  39. Integrating Calorimeter • 20 million 17 GeV electrons per pulse at 120 Hz • 100 MRad radiation dose: Cu/Fused Silica Sandwich • State of the art in ultra-high flux calorimetry • Challenging cylindrical geometry Single Cu plate “ep” ring “Møller” ring End plate Light guide Lead shield PMT holder Lead shield Parity Nonconservation in Møller Scattering

  40. Scattered Flux Profile • ~ 2 mm geometry • 1% energy scale • Radiative tail • < 1% background Parity Nonconservation in Møller Scattering

  41. Backgrounds Parity Nonconservation in Møller Scattering

  42. Pion Detector • ~ 0.5 % pion flux • ~ 1 ppm asymmetry • < 5 ppb correction Parity Nonconservation in Møller Scattering

  43. SLICES: Temporal Beam Profile S1 S2 S3 S4 BPM 12X “Real” Waveform • SLICES readout in 10 bit ADCs Q : bpm31Q (4) E : bpm12X (3) X : bpm41X (4) Y : bpm41Y (4) dX : bpm31X (4) dY : bpm31Y (4) Integration time : S1 : 0 -100 ns S2 : 100-200 ns S3 : 200-300 ns S3 : 300-1000 ns Parity Nonconservation in Møller Scattering

  44. Additional Corrections trouble Better ! • OUT detector at edge of Møller acceptance most sensitive to beam systematics • Use it to set limits on the grand asymmetry OUT detector asymmetry vs sample OUT asymmetry with SLICE correction Parity Nonconservation in Møller Scattering

  45. EP Sample: Summary Preliminary (raw asymmetries) ARAW(45 GeV) = -1.36 ± 0.05 ppm (stat. only) ARAW(48 GeV) = -1.70 ± 0.08 ppm (stat. only) • Ratio of asymmetries: • APV(48 GeV) /APV(45 GeV) = 1.25 ± 0.08 (stat) ± 0.03 (syst) • Consistent with expectations for inelastic ep asymmetry, but hard to interpret in terms of fundamental parameters • 35±10 ppb correction to Møller asymmetry in Run I, below 20 ppb for Run II • Test of strong interactions in E158 ? Parity Nonconservation in Møller Scattering

  46. ATep at E158 • Raw asymmetry! • Has the opposite sign! (preliminary) • Polarization & background corrections • ~ 25% inelastic ep • Few percent pions (asymmetry small) • Proton structure at E158 ! Moller ring ep ring f (Azimuthal angle) 43 & 46 GeV ep  ep ~ 24 hrs of data Parity Nonconservation in Møller Scattering

  47. Luminosity Monitor more than 108 scattered electrons per spill at lab ~ 1 mrad • Density fluctuations monitor • Null asymmetry test • Enhanced sensitivity to beam fluctuations Parallel plates Parity Nonconservation in Møller Scattering

  48. Luminosity Monitor Data • Null test at level of 20 ppb • Density fluctuations small • Limits on second order effects Parity Nonconservation in Møller Scattering

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