1. SLAC E158: Measuring Parity Violation in Fixed-Target Møller Scattering David Relyea SLAC/Princeton University CIPANP 2003 20 May, 2003 QC1B Main acceptance collimator E158 Goal:  sin 2  W = +/- 0.001 Best measurement of sin 2  W away from the Z-pole

2. 05/20/2003, DRRE158 @ CIPANP2003 Outline Physics Motivation Experimental Technique Data Analysis Results and Interpretations Outlook

3. 05/20/2003, DRRE158 @ CIPANP2003 Parity Violation in Møller Scattering Scatter polarized 50 GeV electrons off unpolarized atomic electrons Measure Small tree-level asymmetry At tree level, (at 90 degrees in CM frame) Raw expected asymmetry about 150 ppb  Goal is to measure it with precision of 8%  Most precise to date measurement of sin 2  W at low Q 2 with  sin 2  W )=0.001

4. 05/20/2003, DRRE158 @ CIPANP2003 E158: Physics Impact Establish running of sin  W to 8  level Sensitivity to new physics: compositeness up to 15 TeV, Z’ (GUTs) to ~1TeV  Complementary to collider limits, different couplings Compositeness Neutral currents (GUTs) Scalar interactions (LFV) RRLL – ee eeee ee Z´ e ee e l+l+ ll q q e e   e e E158 ee RRLL + eeee ee LEPII FNAL

5. 05/20/2003, DRRE158 @ CIPANP2003 Scatter polarized electrons off atomic electrons  High cross section (14  Barn)  High intensity electron beam, ~84% polarization  0.18 r.l. LH2 target (1.5 m) Luminosity 4*10 38 cm -2 s -1  High counting rates  flux-integrating calorimeter Experimental Technique Source Linac End Station A ESA Principal backgrounds: elastic and inelastic ep Main systematics:  Beam polarization  Helicity-correlated beam effects  Backgrounds

6. 05/20/2003, DRRE158 @ CIPANP2003 Parity-Violating Asymmetry 1. Measure asymmetry for each pair of pulses, p, coefficients determined experimentally by regression or from dithering coefficients 2. Correct for difference in R/L beam properties: charge, position, angle, energy R-L differences 3. Obtain physics asymmetry: backgrounds beam polarization

7. 05/20/2003, DRRE158 @ CIPANP2003 1. Electron Beam i) high intensity - 500 kWatt beam power ii) stability - intensity jitter <1% - spotsize jitter <10% - position jitter <10% iii) small left-right asymmetries - intensity - position/angle - energy iv) high (>80%) polarization v) Compatibility with PEPII operation 2. Electron Beam monitoring i) toroid resolution: < 30 ppm per pulse ii) BPM resolution: < 1  m per pulse iii) energy resolution: < 50 ppm per pulse 3. Liquid Hydrogen Target i) target density fluctuations: <10 -4 per pulse ii) 18% radiation length - absorbs 500W beam power iii) Safety (largest LH2 target in the world) 4. Detectors i) detector resolution: <100 ppm per pulse ii) multiple backgrounds iii) radiation damage iv) linearity < 1% Experimental Challenges

8. 05/20/2003, DRRE158 @ CIPANP2003 Beam helicity is chosen pseudo-randomly by using electro-optical Pockels cells in the Polarized Light Source Create pulse quadruplets at 30 Hz Beam asymmetries reduced by using feedback at the Source Control charge asymmetry and position asymmetry Physics Asymmetries can be reversed Insert a half-wave plate in the Source Change the (g-2) spin precession in the A-Line (take 45 GeV and 48 GeV data) “Null Asymmetry” cross-check is provided by a Luminosity Monitor Measures very forward angle e-p (Mott) and Møller scattering False Asymmetries can also be reversed Insert the “-I/+I” Inverter in Polarized Light Source Reverses both false beam position and angle asymmetries Leaves physics asymmetry unchanged Electron Beam: Systematics

9. 05/20/2003, DRRE158 @ CIPANP2003 Experimental Layout: ESA Target chamber Dipoles Precision Beam Monitors Detector Cart Drift pipe Quadrupoles Luminosity Monitor Main Collimators Concrete Shielding 60 m

10. 05/20/2003, DRRE158 @ CIPANP2003 Experimental Layout: Spectrometer Target Dipoles Quadrupoles Dipole chicane allows clean collimation of photons and positrons from target interactions Quadrupoles separate moller and ep flux at detector face (see inset) Main acceptance collimator (upper right corner) accepts mollers in desired momentum/radial range Synchrotron collimators (not shown) block synchrotron radiation Photon Collimator Acceptance Collimator 30 cm 20 cm 0 cm 58 m0 m

11. 05/20/2003, DRRE158 @ CIPANP2003 MOLLER, EP are copper/quartz fiber calorimeters PION is a quartz bar Cherenkov LUMINOSITY is an ion chamber with Al pre-radiator All detectors have azimuthal segmentation, and have PMT readout to 16-bit ADC Experimental Layout: Detectors Primary (Unscattered) Beam Radius (cm) (z axis not to scale)

12. 05/20/2003, DRRE158 @ CIPANP2003 Regression Analysis In addition, independent analysis based on beam dithering

13. 05/20/2003, DRRE158 @ CIPANP2003 Raw Asymmetry Statistics

14. 05/20/2003, DRRE158 @ CIPANP2003 Detector Asymmetry Dipoles Detector divided into 3 rings of PMTs: Inner, Middle and Outer Each ring manifests an asymmetry dipole Asymmetry dipoles can be used to study systematics

15. 05/20/2003, DRRE158 @ CIPANP2003 Beam Systematics Beam systematics are small But, some detector ‘monitors’ show poor  2 and non-zero mean values. X’ sensitivity X sensitivity

16. 05/20/2003, DRRE158 @ CIPANP2003 Should reduce to 10 ppb or lessCurrent systematic error: 18 ppb Use radial and azimuthal segmentation of Moller detector to construct ‘monitors’ that have much larger sensitivity to beam parameters than the Moller ‘monopole’ Beam Parameter Detector MonitorMonitor slope / Moller monopole slope E(OUT-MID) monopole11 XMID xdipole20 YMID ydipole35 X’OUT xdipole37 Y’(OUT-MID) ydipole52 Beam Systematics

17. 05/20/2003, DRRE158 @ CIPANP2003 “ep” Detector Data

18. 05/20/2003, DRRE158 @ CIPANP2003 Run I systematic error should reduce from 24 to less than 15 ppb Run II corrections will be on the order of 25 ppb A PV Corrections and Backgrounds

19. 05/20/2003, DRRE158 @ CIPANP2003 Normalization Errors Beam polarization measured using polarized foil target Same spectrometer used with dedicated movable detector

20. 05/20/2003, DRRE158 @ CIPANP2003 Raw Asymmetry Result (blinded; before corrections and normalization)

21. 05/20/2003, DRRE158 @ CIPANP2003 Moller Physics Asymmetry (unblinded; with corrections and normalization) A PV (e - e - at Q 2 = 0.027 GeV 2 ): -151.9  29.0 (stat)  32.5 (syst) parts per billion (preliminary) Significance of parity nonconservation in Møller scattering: 3.6 

22. 05/20/2003, DRRE158 @ CIPANP2003 Convert to for comparison with other experiments: sin 2  W (Q 2 =0.027 GeV 2 ) = 0.2371 ± 0.0025 (stat) ±0.0027 (syst) (preliminary) Weak Mixing Angle E158 projected

23. 05/20/2003, DRRE158 @ CIPANP2003 Parity is violated in Møller scattering Limit on  LL at the level of 5-6 TeV (90% C.L.) Limits on extra Zs at the level of 300 GeV Limit on lepton-flavor violating coupling ~ 0.02-0.03 G F These numbers are competitive with collider limits Implications

24. 05/20/2003, DRRE158 @ CIPANP2003 A very challenging experiment is producing physics results Parity is violated in Møller scattering Inelastic e-p asymmetry at low Q 2 measured; consistent with quark picture First measurement of e-e transverse asymmetry Run II data are being analyzed; will double statistics Final Run III in July-August 2003 Conclusions Preliminary Run 1 results A PV (Moller) = -151.9 ± 29.0 ±32.5 ppb sin 2  W eff = 0.2371 ± 0.0025 ±0.0027

25. 05/20/2003, DRRE158 @ CIPANP2003 Polarimetry 84.9 +/- 4.4 % polarization throughout Run I

26. 05/20/2003, DRRE158 @ CIPANP2003 Beam Delivery for E158 (April 20 - May 27) 104,000 Peta-Electrons (16.6 Coulombs) 232 Million Spills ~84% Electron Polarization Beam Delivery Efficiency (120Hz running) 72% for 48 GeV, 3.5 x 10 11 65% for 45 GeV, (5-6) x 10 11 48 GeV 3.5 10 11 / Pulse 45 GeV (5-6) 10 11 / Pulse

27. 05/20/2003, DRRE158 @ CIPANP2003 LH 2 Scattering Chamber LH 2 Target Chamber Dipoles Quadrupoles BPM 2 Spectrometer Collimators

28. 05/20/2003, DRRE158 @ CIPANP2003 Charge Asymmetry -85 ± 344 ppb -341 ± 334 ppb 2a-3a = 2.10 ± 5.72 ppb The double-feedback keeps the average charge asymmetry corrections tiny! Avg. correction = -44 ± 332 ppb

29. 05/20/2003, DRRE158 @ CIPANP2003 Energy Asymmetry 1.71 ± 2.60 ppb The two energy BPM’s agree to very high precision! Nulling the charge asymmetry at 1.2 GeV region does indeed seem to help zero the energy asymmetry. 4.9 ± 15.7 ppb

30. 05/20/2003, DRRE158 @ CIPANP2003 POS Loop Performance 2.2 ± 2.5 nm 0.9 ± 5.0 nm Feeding back on ASSET BPM’s, after ~30M pairs: Some A-line BPM’s:

31. 05/20/2003, DRRE158 @ CIPANP2003 Polarized Source Laser System

32. 05/20/2003, DRRE158 @ CIPANP2003 Beam Asymmetry Feedbacks ItemControl Diagnostic Intensity Position IA Pockels Cell Piezo Mirror Toroid (@ 1 GeV) BPM (@ 1 GeV) Algorithm: - measure asymmetry on a run with N pulses (typically 1-30K pulses) - induce asymmetry on next run to cancel measured asymmetry on current run Helicity Control Bench IA CPPS Intensity 1 PD Intensity 2 PD Cleanup polarizer Piezomirror L3L3 Asymmetry inverter -2I-2I +2 I Helicity filter /2 plate remotely insertable Flash:Ti Gives better than 1/sqrt(N) scaling of charge asymmetry, position difference

33. 05/20/2003, DRRE158 @ CIPANP2003 Results: Pion Asymmetry A LR (  ) = 1.6 ppm Estimated correction to A LR ~2 ppb

34. 05/20/2003, DRRE158 @ CIPANP2003 Beam property beam A LR Intensity225 +/- 320 ppb Energy-0.1 +/- 1.4 keV (1.1 +/- 16 ppb) X Position-16.9 +/- 5.6 nm Y Position-3.3 +/- 4.0 nm X Angle0.41 +/- 0.23 nrad Y Angle0.12 +/- 0.07 nrad Polarization84.9 +/- 4.4% Electron Beam: Results

35. 05/20/2003, DRRE158 @ CIPANP2003 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  Q 2 measurement Profile Detector

36. 05/20/2003, DRRE158 @ CIPANP2003 Scattered Flux Profile ~2 mm geometry 1% energy scale Radiative tail <1% background Møller peak scan: data vs Monte Carlo Data Monte Carlo Møller scattering kinematics: = 0.0266 GeV  = 0.6

37. 05/20/2003, DRRE158 @ CIPANP2003 Pion Detector ~ 0.5 % pion flux ~ 1 ppm asymmetry < 5 ppb correction

38. 05/20/2003, DRRE158 @ CIPANP2003 Acceptance Collimator Collimators

39. 05/20/2003, DRRE158 @ CIPANP2003 Luminosity Monitor Data Null test at level of 20 ppb Target density fluctuations small Limits on second order effects

40. 05/20/2003, DRRE158 @ CIPANP2003  Null asymmetry measurement  Enhanced sensitivity to beam fluctations and target density fluctuations. beam Segmented ion chamber detector with Aluminum preradiator. 500W incident power (50W from synchrotron radiation) Signal: Motts and high energy Mollers 350M electrons per pulse; ~40 GeV A PV ~ -10ppb Luminosity Monitor

41. 05/20/2003, DRRE158 @ CIPANP2003 Statistical and Systematic Fluctuations Integrate Detector response: Flux Counting

42. 05/20/2003, DRRE158 @ CIPANP2003 a 2% required for physics measurement; 1% for accelerator operation Electron Beam: Delivery Summary ITEMGoalRun I (2002) Beam Charge 6 x 10 11 Intensity Jitter 2% rms a 0.5% rms Position Jitter <10% of spotsize5% of spotsize Spotsize Jitter <10% of spotsize5% of spotsize Energy Spread 0.3% rms0.1% rms Energy Jitter 0.2% rms0.03% rms Polarization 75%~85%

43. 05/20/2003, DRRE158 @ CIPANP2003 DeviceGoalTestsRun I results a Target BPM x,y 1  m0.5  m 2  m Target BPM x’,y’ 0.4  rad0.03  rad 0.1  rad Energy BPM b 30 ppm 40 ppm Target Toroid 30 ppm 60 ppm a Relaxed goals for Run I (due to statistics) b Energy goal ignores detector calorimetric compensation for 1/E – dependence of Møller cross section Electron Beam: Monitor Resolutions Resolution goals are to achieve 1ppb error after 600M pulses for each of x, x’, y, y’, E, I Agreement (MeV)  toroid  30 ppm  BPM  2 microns  energy  1 MeV BPM24 X (MeV) BPM12 X (MeV) Resolution 1.05 MeV

44. 05/20/2003, DRRE158 @ CIPANP2003 Moller Asymmetry (Blinded) Based on analysis of 146M spills collected in April-May 2002 Asymmetry blinded to avoid bias (expect ~  150 ppb)

45. 05/20/2003, DRRE158 @ CIPANP2003 Results: Systematic Check Experiment run at 2 energies (for g-2 asymmetry flip) Equal data samples taken at both half-wave plate settings

46. 05/20/2003, DRRE158 @ CIPANP2003 Results: Asymmetry Pulls Per Run Expect a mean of 0 and an RMS of 1

47. 05/20/2003, DRRE158 @ CIPANP2003 Results: Statistics and Systematics Asymmetry pulls per event pair: 17M spills (about 2 days of data) Average asymmetry width: 195 ppm

48. 05/20/2003, DRRE158 @ CIPANP2003 Physics Runs Run 2 Run 1 10 20 Electrons on Target Energy#days @120Hz # Peta-Electron#spillsAverage Charge Production Efficiency* Run I45.6 GeV19.267K125M5.5 x 10 11 63% Run I48.8 GeV14.837K105M3.5 x 10 11 69% Run II45.6 GeV15.256K113M5.2 x 10 11 72% Run II48.8 GeV19.063K153M4.3 x 10 11 78% Run I: April 23 12:00 – May 28 00:00 (this result) Run II: October 10 08:00 – November 13 16:00 *Efficiency is avg. delivered rate normalized to 119Hz Run I with PEPII, Run II dedicated One g-2 flip in each run /2 flip roughly once in two days Asymmetry inverter flip once a week Run I data divided into 24 “slugs”

49. 05/20/2003, DRRE158 @ CIPANP2003 E158 Collaboration Institutions CaltechSyracuse PrincetonJefferson Lab SLACUC Berkeley SaclayUMass Amherst Smith CollegeU. of Virginia 65 physicists 5 grad students Sept 1997: 1998: 1999: 2000: 2001: Spring 2002: Fall 2002: Summer 2003: 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)

50. 05/20/2003, DRRE158 @ CIPANP2003 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.

51. 05/20/2003, DRRE158 @ CIPANP2003 Refrigeration Capacity1000W Max. Heat Load: - Beam500W - Heat Leaks200W - Pumping100W Length1.5 m Radiation Lengths0.18 Volume47 liters Flow Rate 10 m/s Reynolds number in target cell 10 6 Disk 1 Disk 2 Disk 3 Disk 4 Wire mesh disks in the target introduce turbulence at the 2mm scale and a transverse velocity component. Total of 8 disks in the target. Experimental Layout: Liquid Hydrogen Target

52. 05/20/2003, DRRE158 @ CIPANP2003 electron flux Basic Idea: : quartz : copper light guide PMT shielding air MOLLER Detector

53. 05/20/2003, DRRE158 @ CIPANP2003 Not shown: Møller Polarimeter in ESA Synchrotron Light Monitor before momentum slits Energy dithered by using sub-booster phases for Sectors 27, 28 Electron Beam: Diagnostics Thermionic Gun Polarized Gun BPMs (3) Toroids (2) 1 GeV Accelerator 48 GeV Angle BPMs (2) Position BPMs (2) Toroids (2 pair) Wire Array Dispersive (Energy) BPMs (2) Momentum Defining Slits Dithering Coils for x, x’, y, y’

54. 05/20/2003, DRRE158 @ CIPANP2003 Transverse Asymmetry ~ 3 ppm up-down asymmetry with 85% transverse polarization Flips sign with g-2 precession → physics ! Two-photon exchange QED effect: Calculation does not exist in the literature Data carefully re-weighted to maintain azimuthal symmetry Asymmetry vs 