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

Steve Rock University of Massachusetts Zeuthen For SLAC E158 Collaboration. From Z 0 to Zero: A Precise Measurement of the Running of the Weak Mixing Angle SLAC E158. Outline. History Physics Motivation Technique for Precision Measurement Beam LH 2 Target Spectrometer Detectors

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

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  1. Steve Rock University of Massachusetts Zeuthen For SLAC E158 Collaboration From Z0 to Zero:A Precise Measurement of the Running of the Weak Mixing Angle SLAC E158

  2. Outline History Physics Motivation Technique for Precision Measurement Beam LH2 Target Spectrometer Detectors Analysis Results Outlook

  3. SLAC E122 (1978) e-D Inelastic Scattering Detector e Liquid Deuterium 16 – 22 GeV Measured Coupling of electron and nucleons sin2W = 0.224 + 0.020 First definitive measurement of mixing between the weak and electromagnetic interaction Help Establish the Standard Model

  4. IMPROVEMENTS HIGHER POLARIZATION (NLC) BEAM STABILITY (SLC, FFTB) 50 GeV BEAM 5  LONGER TARGET RADIATION RESISTANT DETECTOR (LHC) LOW NOISE, HIGH RESOLUTION ELECTRONICS

  5. Based on gauge group SU(2)L X U(1) with isotriplet field W and isosinglet field B SU(2)L coupling is g, U(1) coupling is g' After spontaneous symmetry breaking via Higgs mixing of W and B fields produces observed particles Charged bosons Neutral bosons Vector couplings Axial couplings fermion charge q/e fermion weak isospin Standard Model Electroweak Theory

  6. LH coupling RH coupling Standard Model W and g determine ALL couplings

  7. “High Energy” EW Data • Spectacular precision at LEP, SLD • 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 Belle, BaBar, E158, g-2,…

  8. Parity Violation at the Z-pole (SLD at SLAC) sin2W at Z pole

  9. sin2W = e2/g2 → test gauge structure of SU(2)U(1) Running of Weak Mixing Angle 3%

  10. Beyond the Standard Model Find new physics by deviations from SM predictions Precision EW via PV e e e e e e New physics ~|amplitude| Make high mass exchange visible + ?  Z APV ~ Beat large against small to see new

  11. γ-Z INTERFERENCEAT LOW Q2 • Interference proportional to Q2 • Sensitive to Z’

  12. Precise Low Q2 PVExperiments Moller- E158 DIS-Parity Q-Weak(JLAB) Atomic Parity V e  e e e e e e Z Z   Cs133 Z  e p e Z n Pure leptonic, Incoherent Coherent quarks Coherent quarks isoscalar quarks proton entire nucleus This Experiment Well understood Results ~2008 Large syst. errors small corrections atomic, nuclear structure No quarks (2C1u-C1d)+Y(2C2u-C2d) -2(2C1u+C1d) -376C1u- 422C1d

  13. Parity Violation in Møller Scattering • Scatter polarized 50 GeV electrons off unpolarized atomic electrons • Measure • Small tree-level asymmetry 1-4sin2qw ~ 0 At tree level, (smaller after radiative effects) • Raw asymmetry about 130 ppb • Measure it with precision of 10% • Most precise measurement of sin2W at low Q2

  14. E158 New Physics Reach Compositeness  ~ 10 TeV Grand Unified Theories MZ’ ~ 0.8 TeV ~ 0.01GF0.01

  15. SLAC E-158 integrating flux counter L ~ 1038cm-2s-1 5x1011 e-/pulse 2 GHz 45 GeV 4-7 mrad LH2 P=85% End Station A

  16. E158 Collaboration • SLAC • Smith College • Syracuse • UMass • Virginia • UC Berkeley • Caltech • Jefferson Lab • Princeton • Saclay 7 Ph.D. Students 60 physicists Sep 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)

  17. TINY ASYMMETRY EXPRIMENT ( ) (STABILITY AND INTENSITY) • HIGH INTENSITY POLARIZID e- BEAM • HIGH DENSITY ELECTRON TARGET (LH2) • BACKGROUND REMOVERS • MOLLER ELECTRON SELECTORS • DETECTORS • MONITORS

  18. Scattering of polarized electrons off atomic electrons • High cross section (14 Barn) • High intensity electron beam, ~85% 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 Experimental Technique

  19. Major Challenges • Statistics ! • Need to accumulate ~1016 scattered electrons • Suppress Random noise • Want to be dominated by counting statistics • Beam pulse to pulse “random” fluctuations are major (potential) source of additional “statistical error • Systematics • False asymmetries • Backgrounds (Need to measure insitu)

  20. Statistics # scattered e- per pulse 107/pulse Rep rate (120 Hz) 109 /sec Seconds/day 1014/day 100 days 1016 A ~ 10-8

  21. Control of Beam Systematics • Beam helicity is chosen pseudo-randomly at 120 Hz • sequence of pulse quadruplets • use electro-optical Pockels cell in Polarized Light Source • Reduce beam asymmetries by feedback • Control charge and position asymmetry at Source • Control Angle Asymmetry • Control Energy Asymmetry

  22. E-158 Beam (and comparison with 500 GeV Linear Collider Design) Parameter E-158 NLC-500 Charge/Train 5 x 1011 14.4 x 1011 Repetition Rate 120 Hz 120 Hz Energy 45 GeV 250 GeV e- Polarization 85% 85% Train Length 270ns 267ns Microbunch spacing 0.3ns 1.4ns Beam Loading 13% 22% Energy Spread 0.15% 0.16%

  23. BEAM HIGH INTENSITY 6×1011 /burst HIGH POLARIZATION “HIGH ENERGY” (Asymmetry  Q2 ) STABLE (Same Beam for L & R Polarization) INTENSITY (acceleration, Target) POSITION (Acceptance, backgrounds) ANGLE (σ depends on θ) ENERGY (σ depends on E) TRANSVERSE SIZE (Target effects)

  24. Polarized Source

  25. 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

  26. BEAM VARIATIONS • LONG TERM DRIFTS CONTROLLED WITH FEEDBACK • LASER OPTICS • LASER INTENSITY • POCKEL CELLS • ACCELERATING CAVITY • STEERING MAGNETS

  27. 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

  28. BEAM VARIATIONS • BEAM JITTER (OFFLINE CORRECTIONS) • ENERGY • ANGLES • POSITION (and correlation with time) • INTENSITY • BEAM SIZE • TARGET DENSITY • MONITOR EFFECTS OF VARIATION • “NATURAL JITTER” (Linear Regression) • CONTROLLED VARIATION • CORRECT PULSE BY PULSE

  29. Eliminating Beam Jitter i Determined by Linear Regression i Determined by Dithering Both Methods agree 128 1 - -202-

  30. Moller Detector Regression Corrections In addition, independent analysis based on beam dithering

  31. 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) • Reverse special laser optics • 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

  32. End Station A

  33. Target chamber Quadrupoles Detector Cart Concrete Shielding Precision Beam Monitors Luminosity Monitor Dipoles Drift pipe Main Collimators 60 m Experimental Layout in ESA

  34. Liquid Hydrogen Target CONSTANT DENSITY Refrigeration Capacity 1000W Max. Heat Load: - Beam 500W - Heat Leaks 200W - Pumping 100W Length 1.5 m Radiation Lengths 0.18 Volume 47 liters Flow Rate 5 m/s Disk 1 Disk 2 Disk 3 Disk 4 Wire mesh disks in target cell region to introduce turbulence at 2mm scale and a transverse velocity component. Total of 8 disks in target region.

  35. SPECTROMETER & DETECTORS • Separate Moller e- from other processes • Accurately measure number of Moller e- • Measure Q2 • Measure Backgrounds • Pions • e- p  e- p +? (BIGGIST CORRECTION) • Neutrons, , …

  36. E158 Spectrometer Forward background of e+ e- pairs Line-of-sight shielding requires a “chicane” Moller ring is 20 cm from the beam Emoller~25 GeV

  37. Detectors ~1.5 mr ~1.5o MOLLER, ep are copper/quartz fiber calorimeters PION is a quartz bar Cherenkov LUMI is an ion chamber with Al pre-radiator All detectors have azymuthalsegmentation, and PMT readout to 16-bit ADC

  38. Profile Detector: Q² Cerenkov detector Linear drive Bearing wheels 4 Quartz Cherenkov detectors with PMT readout insertable pre-radiators insertable shutter in front of PMTs Radial and azymuthal scans • collimator alignment, spectrometer tuning • background determination • Q2 measurement • Monte Carlo Tune

  39. e p Background • MEASURE • e p Asymmetry in e p Detector • Shape of e p and e e in Profile Detector using Movable Collimators • MODEL ASYMMETRY(Q2,W2) • Monte Carlo using Detector Acceptance • Tuned with Profile Detector • Quads on/off • Collimator Positions • CORRECTION ~ -25 ±5 ppb

  40. APV Measurement 1. Measure asymmetry for each pair of pulses 2. Correct for difference in R/L beam properties, charge, position, angle, energy R-L differences coefficients determined experimentally by regression or from dithering coefficients 3. Sum over all pulse pairs, 4. Obtain physics asymmetry: backgrounds dilutions beam polarization

  41. 3 EXPERIMENTAL RESULTS • e e TRANSVERSE ASYMMETRY • 2 photon exchange physics • e p LONGITUDINAL ASYMMETRY • Proton Structure • e e LONGITUDINAL (main result)

  42. e e Transverse Asymmetries Beam-Normal Asymmetry in elastic electron scattering • Beam Polarization Perpendicular to Direction of motion • Select by beam energy (number of spin rotations) • Azimuthal Dependence of Asymmetry Interference between one- and two-photon exchange

  43. Raw asymmetry! • Publication by Fall • Crosscheck E158 polarimetry at 3%? • O(3) test of QED in E158 ? • ~5% residual transverse polarization in longitudinal data: carefully combine detector channels to suppress this effect E158 e- e- Transverse Results ~ 24 hrs of data 43 and 46 GeV ee  ee LH2 target  (Azimuthal angle)

  44. ep Detector Data (Run 1) 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

  45. Møller Asymmetry (Blind Analysis) • Over 330M pulse pairs over 3 separate runs (2002-2003) at Ebeam=45 and 48 GeV • Passively flip helicity of electrons wrt source laser light ~every day to suppress spurious helicity-correlated biases

  46. Asymmetry pulls per pulse pair: 150M pairs Asymmetry pulls per 10k pair “chunks” Raw Asymmetry Statistics (A-<A>)/

  47. Correction fbkg fbkg) Acorr (ppb) Acorr) (ppb) Beam asymmetries - - - 4 Beam spotsize - - 0 1 Transverse asymmetry - - -4 2 ep elastic 0.058 0.007 -8 2 ep inelastic 0.009 0.003 -22 6 High energy photons 0.004 0.002 +3 3 Synchrotron photons 0.0015 0.0005 0 2 Neutrons 0.0006 0.0002 -1 1 Brem and Compton electrons 0.005 0.002 0 1 Pions 0.001 0.001 1 1 TOTAL 0.082 0.009 -27 8 • Scale factors: • Average Polarization 88 ± 5% • Linearity 99 ± 1% • Radiative corrections: 1.016 ± 0.005 Asymmetry Corrections and Systematics

  48. from APV to sin2Weff where: is an analyzing power factor; depends on kinematics and experimental geometry. Uncertainty is 1.7%. (y = Q2/s)

  49. 7 Running of the Weak Mixing Angle

  50. The Weak Mixing Angle • General agreement between low Q2 experiments, although NuTeV is still 3 high compared to SM fit • Stringent limits on new interactions at multi-TeV scales • Parameterize as limit on 4-fermion contact term LL : 6-14 TeV limits for E158 alone (95% C.L.) • Limit on SO(10) Z' at 900 GeV

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