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

E158 Steve Rock Nov 04 Outline History Physics Motivation Technique for Precision Measurement  Beam  LH 2 Target  Spectrometer  Detectors  Analysis Results Outlook

E158 Steve Rock Nov 04 Detector e 16 – 22 GeV Liquid Deuterium sin 2  W = SLAC E122 (1978) e-D Inelastic Scattering Measured Coupling of electron and nucleons First definitive measurement of mixing between the weak and electromagnetic interaction Help Establish the Standard Model

E158 Steve Rock Nov 04 IMPROVEMENTS HIGHER POLARIZATION (NLC) BEAM STABILITY (SLC, FFTB) 50 GeV BEAM 5  LONGER TARGET RADIATION RESISTANT DETECTOR (LHC) LOW NOISE, HIGH RESOLUTION ELECTRONICS

E158 Steve Rock Nov 04 Standard Model Electroweak Theory 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 weak isospin fermion charge q/e

E158 Steve Rock Nov 04 Standard Model  W and g determine ALL couplings  W and g determine ALL couplings LH couplingRH coupling

E158 Steve Rock Nov 04 “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,…

E158 Steve Rock Nov 04 Parity Violation at the Z-pole (SLD at SLAC) sin 2  W at Z pole

E158 Steve Rock Nov 04 Running of Weak Mixing Angle sin 2  W = e 2 /g 2 → test gauge structure of SU(2)  U(1) 3%

E158 Steve Rock Nov 04 Beyond the Standard Model Precision EW via PV New physics ~|amplitude| Make high mass exchange visible A PV ~ Find new physics by deviations from SM predictions ee  e ? e Beat large against small to see new + ee Z

E158 Steve Rock Nov 04 γ-Z INTERFERENCE AT LOW Q 2 Interference proportional to Q 2 Sensitive to Z ’

E158 Steve Rock Nov 04 Precise Low Q 2 PV Experiments ee  e e Z ee  Z ee  Z e  Z Moller- E158 DIS-Parity Q-Weak(JLAB) Atomic Parity V 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 Cs 133 p n No quarks (2C 1u -C 1d )+Y(2C 2u -C 2d ) -2(2C 1u +C 1d ) -376C 1u - 422C 1d

E158 Steve Rock Nov 04 Parity Violation in Møller Scattering Scatter polarized 50 GeV electrons off unpolarized atomic electrons Measure Small tree-level asymmetry 1-4sin 2  w  At tree level, (smaller after radiative effects) Raw asymmetry about 130 ppb –Measure it with precision of 10% –Most precise measurement of sin 2  W at low Q 2

E158 Steve Rock Nov 04 E158 New Physics Reach Compositeness  ~ 10 TeV Grand Unified Theories M Z’ ~ 0.8 TeV ~ 0.01G F 0.01

E158 Steve Rock Nov 04 SLAC E GHz 45 GeV P=85% 5x10 11 e - /pulse L ~ cm -2 s -1 integrating flux counter LH2 4-7 mrad End Station A

E158 Steve Rock Nov 04 UC Berkeley Caltech Jefferson Lab Princeton Saclay SLAC Smith College Syracuse UMass Virginia 7 Ph.D. Students 60 physicists Sep 97: EPAC approval : Design and Beam Tests 2000: Funding and construction 2001: Engineering run 2002: Physics Runs 1 (Spring), 2 (Fall) 2003: Physics Run 3 (Summer) E158 Collaboration

E158 Steve Rock Nov 04 TINY ASYMMETRY EXPRIMENT ( ) (STABILITY AND INTENSITY) HIGH INTENSITY POLARIZID e - BEAM HIGH DENSITY ELECTRON TARGET (LH 2 ) BACKGROUND REMOVERS MOLLER ELECTRON SELECTORS DETECTORS MONITORS

E158 Steve Rock Nov 04 Scattering of polarized electrons off atomic electrons  High cross section (14  Barn)  High intensity electron beam, ~85% polarization  1.5m LH2 target  Luminosity 4*10 38 cm -2 s -1  High counting rates: flux-integrating calorimeter Principal backgrounds: elastic and inelastic ep Main systematics: beam polarization, helicity-correlated beam effects, backgrounds Experimental Technique

E158 Steve Rock Nov 04 Major Challenges Statistics !  Need to accumulate ~10 16 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 in situ)

E158 Steve Rock Nov 04 # scattered e - per pulse 10 7 /pulse Rep rate (120 Hz) 10 9 /sec Seconds/day /day 100 days  A ~ Statistics

E158 Steve Rock Nov 04 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 Control of Beam Systematics

E158 Steve Rock Nov %0.15% Energy Spread 85% e - Polarization 250 GeV45 GeV Energy 120 Hz Repetition Rate 14.4 x x Charge/Train 22%13% Beam Loading 1.4ns0.3ns Microbunch spacing 267ns270ns Train Length NLC-500E-158Parameter E-158 Beam (and comparison with 500 GeV Linear Collider Design)

E158 Steve Rock Nov 04 BEAM HIGH INTENSITY 6×10 11 /burst HIGH POLARIZATION “HIGH ENERGY” (Asymmetry  Q 2 ) 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)

E158 Steve Rock Nov 04 Polarized Source

E158 Steve Rock Nov 04 RF Cavity BPM Pulse-to-pulse monitoring of beam asymmetries and resolutions: Agreement (MeV)  toroid  30 ppm  BPM  2 microns  energy  1 MeV BPM24 X (MeV) BPM12 X (MeV) Resolution 1.05 MeV Energy dithering region Beam Diagnostics linac A-Line

E158 Steve Rock Nov 04 BEAM VARIATIONS LONG TERM DRIFTS CONTROLLED WITH FEEDBACK  LASER OPTICS  LASER INTENSITY  POCKEL CELLS  ACCELERATING CAVITY  STEERING MAGNETS

E158 Steve Rock Nov 04 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

E158 Steve Rock Nov 04 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

E158 Steve Rock Nov 04 Eliminating Beam Jitter  i Determined by Linear Regression  i Determined by Dithering Both Methods agree

E158 Steve Rock Nov 04 In addition, independent analysis based on beam dithering Moller Detector Regression Corrections

E158 Steve Rock Nov 04 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 Reversals and Checks

E158 Steve Rock Nov 04 End Station A

E158 Steve Rock Nov 04 Target chamber Dipoles Precision Beam Monitors Detector Cart Drift pipe Quadrupoles Luminosity Monitor Main Collimators Concrete Shielding 60 m Experimental Layout in ESA

E158 Steve Rock Nov 04 Liquid Hydrogen Target Refrigeration Capacity1000W Max. Heat Load: - Beam 500W - Heat Leaks 200W - Pumping 100W Length1.5 m Radiation Lengths0.18 Volume47 liters Flow Rate5 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. CONSTANT DENSITY

E158 Steve Rock Nov 04 SPECTROMETER & DETECTORS Separate Moller e - from other processes Accurately measure number of Moller e - Measure  Q 2  Measure Backgrounds  Pions  e - p  e - p +? (BIGGIST CORRECTION)  Neutrons, , …

E158 Steve Rock Nov 04 Moller ring is 20 cm from the beam Forward background of e + e - pairs Line-of-sight shielding requires a “chicane” E158 Spectrometer E moller ~25 GeV

E158 Steve Rock Nov 04 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 azymuthal segmentation, and PMT readout to 16-bit ADCDetectors  ~1.5 o  ~1.5 mr

E158 Steve Rock Nov 04 Profile Detector:  Q²  Bearing wheels Linear drive Cerenkov detector 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  Q 2 measurement  Monte Carlo Tune

E158 Steve Rock Nov 04 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(Q 2,W 2 )  Monte Carlo using Detector Acceptance  Tuned with Profile Detector  Quads on/off  Collimator Positions CORRECTION ~ -25 ±5 ppb

E158 Steve Rock Nov 04 A PV Measurement 1. Measure asymmetry for each pair of pulses 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. Sum over all pulse pairs, 4. Obtain physics asymmetry: backgrounds beam polarization dilutions

E158 Steve Rock Nov 04 3 EXPERIMENTAL RESULTS e e TRANSVERSE ASYMMETRY  2 photon exchange physics e p LONGITUDINAL ASYMMETRY  Proton Structure e e LONGITUDINAL (main result)

E158 Steve Rock Nov 04 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

E158 Steve Rock Nov 04 E158 e - e - Transverse Results 43 and 46 GeV ee  ee LH2 target ~ 24 hrs of data 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  (Azimuthal angle)

E158 Steve Rock Nov 04 ep Detector Data (Run 1) Ratio of asymmetries: A PV (48 GeV) /A PV (45 GeV) = 1.25 ± 0.08 (stat) ± 0.03 (syst) A RAW (45 GeV) = ± 0.05 ppm (stat. only) A RAW (48 GeV) = ± 0.08 ppm (stat. only)  Consistent with expectations for inelastic ep asymmetry

E158 Steve Rock Nov 04 Møller Asymmetry (Blind Analysis) Over 330M pulse pairs over 3 separate runs ( ) at E beam =45 and 48 GeV Passively flip helicity of electrons wrt source laser light ~every day to suppress spurious helicity-correlated biases

E158 Steve Rock Nov 04 Raw Asymmetry Statistics Asymmetry pulls per 10k pair “chunks” Asymmetry pulls per pulse pair:150M pairs (A- )/ 

E158 Steve Rock Nov ep elastic ep inelastic Brem and Compton electrons Pions TOTAL Neutrons Synchrotron photons High energy photons 2-4--Transverse asymmetry 10--Beam spotsize 4---Beam asymmetries  A corr ) (ppb) A corr (ppb)  f bkg ) f bkg Correction Asymmetry Corrections and Systematics Scale factors: Average Polarization 88 ± 5% Linearity 99 ± 1% Radiative corrections: ± 0.005

E158 Steve Rock Nov 04 from A PV to sin 2  W eff where: is an analyzing power factor; depends on kinematics and experimental geometry. Uncertainty is 1.7%. (y = Q 2 /s)

E158 Steve Rock Nov 04 Running of the Weak Mixing Angle 77

E158 Steve Rock Nov 04 The Weak Mixing Angle General agreement between low Q 2 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

E158 Steve Rock Nov 04 Preliminary Results  Significance of parity non-conservation in Møller scattering: 8  A PV (e - e - at Q 2 =0.026 GeV 2 ) =  128  14 (stat)  12 (syst) sin 2  eff (Q 2 =0.026 GeV 2 ) = ± (stat) ± (syst)  Most precise measurement at low Q 2  Significance of running of sin 2  W : 7  sin 2  W MS (M Z ) = ± (stat) ± (syst)  Standard Model pull: +1.2 

E158 Steve Rock Nov 04 Outlook Next set of precision measurements on the horizon  Neutrino-electron scattering  Reactor experiments (in conjunction with  13 ): cross section measurements to % would translate in  (sin 2  W ) down to ~0.001  Ultimate measurements at the neutrino factory  Atomic parity violation  Ratios of APV in isotopes and hydrogenic ions could reach sensitivity of  (sin 2  W ) ~  PV in electron scattering  Active program planned for JLab: PV in elastic ep scattering (~2007), Møller scattering, and DIS eD scattering (~2010) could reach below  (sin 2  W ) ~ per experiment  e  e  and e  e  at the Linear Collider

E158 Steve Rock Nov 04 Selected Future Measurements 1GeV GeV 100GeV1TeV0.1GeV0.01GeV 133 Cs PNC Single Isotope 168 Yb Yb PNC Isotopic Chain SLAC E158 Møller Scattering JLab Proton Weak Charge NuTev Neutrino- Nucleon Scattering LEP + SLAC Measurements At Z Pole Linear Collider In e + e - and e - e - Modes sin 2 (  W ) Q JLab DIS-parity

E158 Steve Rock Nov 04 CONCLUSIONS sin 2  W RUNS STANDARD MODEL STILL OK MANY MORE TESTS IN FUTURE