1 May The E158 Experiment A Precision Measurement of the Weak Mixing Angle in Fixed Target electron-electron (Møller) Scattering Krishna Kumar University of Massachusetts, Amherst PAVI06, May 16, 2006

2 May The E158 Experiment Outline Physics Motivation Evolution of the E158 Proposal Experimental Design Final Result & Implications Future Prospects with M ø ller Scattering

3 May The E158 Experiment Beyond the Standard Model Rare or Forbidden Processes neutrinoless double-beta decay… Low Q 2 offers unique and complementary probes of “new physics” Low Energy: Q 2 << M Z 2 Symmetry Violations Neutrino oscillations, EDM searches… New Particle Searches Rare or Forbidden Processes Symmetry Violations Electroweak One-Loop Effects Complementary Approaches High Energy Colliders SLC, LEP, LEPII, HERA, Tevatron, PEPII, LHC… Indirect Effects of “New Physics” g-2 anomaly, CKM Unitarity weak neutral current interactions (WNC)

4 May The E158 Experiment Precision WNC Low Q 2 Precise 0.1% Indirect access to TeV scale World electroweak data has marginal  2, but no discernable pattern Data used to put limits on energy scale of new physics effects Parity-conserving contact interactions probed at 10 TeV level Parity-violating contact interactions probed at 1 TeV level

5 May The E158 Experiment Evolution of an Idea Figure of Merit rises linearly with E lab Depending on the day of the week, I get zero or 16/9ths times the e-p asymmetry Purely leptonic reaction

6 May The E158 Experiment Anatomy of a SLAC Proposal ~ 10 ppb statistical error at highest E beam ~ 0.4% error on weak mixing angle 10 nm control of beam centroid on target –R&D on polarized source laser transport elements 12 microamp beam current maximum –1.5 meter Liquid Hydrogen target 20 Million electrons per 120 Hz –200 ppm pulse-to-pulse statistical fluctuations Electronic noise and density fluctuations < Pulse-to-pulse monitoring resolution ~ 1 micron Pulse-to-pulse beam fluctuations < 100 microns –100 Mrad radiation dose from scattered flux State-of-the-art radiation-hard integrating calorimeter Full Azimuthal acceptance with  lab ~ 5 mrad –Quadrupole spectrometer –Complex collimation and radiation shielding issues

7 May The E158 Experiment E158 Collaboration & Chronology Parity-Violating Left-Right Asymmetry In Fixed Target Møller Scattering Berkeley Caltech Jefferson Lab Princeton Saclay SLAC Smith Syracuse UMass Virginia 8 Ph.D. Students 60 physicists E158 Collaboration At the Stanford Linear Accelerator Center Feb 96: Workshop at Princeton Sep 97: SLAC EPAC approval Mar 98: First Laboratory Review 1999: Design and Beam tests 2000: Funding and construction 2001: Engineering run : Physics 2004: First PRL : Final publications E158 Chronology Goal: error small enough to probe TeV scale physics

8 May The E158 Experiment E158 New Physics Reach

9 May The E158 Experiment Stanford Linear Accelerator Center

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

11 May The E158 Experiment Systematic Control CID Gun Vault Source Laser Room IA Feedback Loop IA cell applies a helicity-correlated phase shift to the beam. The cleanup polarizer transforms this into intensity asymmetry. POS Feedback Loop Piezomirror can deflect laser beam on a pulse-to-pulse basis. Can induce helicity-correlated position differences. “Double” Feedback Loop Adjusts  CP,  PS to keep IA & Piezo corrections small (~ ppm & ~100 nm). Very slow feedback (n = 24k pairs).

12 May The E158 Experiment  toroid  30 ppm  BPM  2 microns  energy  1 MeV Beam Monitoring Agreement (MeV) Resolution 1.05 MeV Event by event monitoring at 1 GeV and 45 GeV

13 May The E158 Experiment Liquid Hydrogen Target Refrigeration Capacity 1 kW Operating Temperature 20 K Length 1.5 m Flow Rate 5 m/s Vertical Motion 6 inches

14 May The E158 Experiment Kinematics

15 May The E158 Experiment Quadupoles and Dipoles Major Breakthrough: 7 magnetic elements from historic 8 and 20 GeV spectrometer elements

16 May The E158 Experiment E158 Spectrometer

17 May The E158 Experiment Downstream Configuration

18 May The E158 Experiment Detector Concept Data from Profile Detectors

19 May The E158 Experiment 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 End plate “ep” ring “Møller” ring Lead shield PMT holder Light guide

20 May The E158 Experiment Profile Detector wheel Luminosity Monitor region PMT Lead Holder/shield Detector Cart Profile Detector wheel PMT Lead Holder/shield

21 May The E158 Experiment E158 Analysis electron flux Basic Idea: : quartz : copper light guide PMT shielding air Radial and azimuthal segmentation Corrections for beam fluctuations Average over runs Statistical tests Beam polarization and other normalization

22 May The E158 Experiment Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003 Physics Runs Electrons on Target 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, GeV: 14.0 revs g-2 spin precession 48 GeV: 14.5 revs Data divided into 75 “slugs”: - Wave plate flipped ~ few hours - Beam energy changed ~ few days A PV Sign Flips

23 May The E158 Experiment Beam Asymmetries Position differences < 20 nm Position agreement ~ 1 nm Charge asymmetry at 1 GeV Charge asymmetry agreement at 45 GeV Energy difference in A line Energy difference agreement in A line

24 May The E158 Experiment Raw Asymmetry Statistics  i ≈ 200 ppm N = 85 Million  i ≈ 600 ppb N = 818

25 May The E158 Experiment A PV = (-131 ± 14 ± 10) x Final Analysis of All 3 Runs Phys. Rev. Lett (2005)

26 May The E158 Experiment Electroweak Physics sin 2  W = e 2 /g 2 → test gauge structure of SU(2)  U(1) 3% Czarnecki and Marciano Erler and Ramsey-Musolf Sirlin et. al. Zykonov

27 May The E158 Experiment Status in 1997 Q (GeV) sin 2  w

28 May The E158 Experiment Nature Vol May 2005 NEWS AND VIEWS Status since 2005 * Limit on  LL ~ 7 or 16 TeV * Limit on SO(10) Z’ ~ 1.0 TeV * Limit on lepton flavor violating coupling ~ 0.01G F (95% confidence level) sin 2  eff = ± ± 6 PRL (2005)

29 May The E158 Experiment Møller Scattering with JLab Upgrade Address longstanding discrepancy between hadronic and leptonic Z asymmetries Z pole asymmetries Comparable to single Z pole measurement: shed light on disagreement Best low energy measurement until ILC or -Factory Could be done ~ Jefferson Lab

30 May The E158 Experiment Ultrahigh Precision loop corrections (world average ~0.0002) Compare with mass observed at the LHC: Measure contribution from scalars to quantum loops Colliders will attempt this with A LR and M W but… Systematics are extremely challenging! t Z H b new physics Critical crosscheck of electroweak theory Energy scale to 10 -4, polarimetry to 0.15%

31 May The E158 Experiment Møller Scattering at the ILC E158LC Energy (GeV) Intensity/pulse 4.5   Pulse Rate (Hz)120 PePe 85%90% Time (s) 5   10 7 A LR (ppm)  A LR (ppm)  sin 2 (  W ) Compton Polarimetry K.K, Snowmass 96 Order of magnitude better Parasitic “exhaust” beam Collider measurements unlikely to do better Need 3 or 4 such independent measurements

32 May The E158 Experiment Summary SLAC E158’s main physics result has been published: Parity is violated in Møller scattering Final result with all data: A PV : -131 ± 14 ± 10 ppb Running of weak mixing angle established at 6  sin 2  eff = ± ± New constraints on TeV scale physics Next publications (by late 2006): Inelastic e-p asymmetry at low Q 2 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! Future experiments could improve sensitivity by ~ 2 to 6 An “ultimate” measurement could be done at an LC