Measuring Parity Violation in M

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Measuring Parity Violation in Møller Scattering
First Results from E158

• Imran Younus
• Syracuse University
• NuFact 2003
• New York, June 09 2003

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OUTLINE

• Motivation
• The experiment
  How to measure 100 ppb
  asymmetries
• Data
• Preliminary results

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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

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Summary of Electroweak Data
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World Electroweak Data
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Electroweak Physics Away from Z pole

• Push to lower or higher energies, away from the
  Z resonance

E158 Electron-electron parity violation at low Q
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Fixed Target Møller Scattering
Purely leptonic reaction gee 1 - 4sin2?W
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E158 Physics Impact

• Unique window of opportunity
• Complementary to collider searches

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Parity Violation in Møller Scattering

• Scatter polarized 50 GeV electrons
• off unpolarized atomic electrons
• Measure
• Small tree-level asymmetry
• At tree level,
• Raw asymmetry about 130 ppb
• Goal is to measure it with precision of 8 (10
  ppb)
• Most precise measurement of sin2qW at low Q2 with
  s(sin2qW)lt0.001

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Running of sin2qW
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E158 Collaboration
Institutions
Caltech Syracuse Princeton Jefferson
Lab SLAC UC Berkeley CEA Saclay UMass
Amherst Smith College U. of Virginia
60 physicists, 7 Ph.D. students
Chronology
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Parity-Violating Asymmetry
Measure pulse-pair flux asymmetry
Correct for difference in R/L beam properties
charge, position, angle, energy R-L differences
coefficients determined experimentally
Physics asymmetry
backgrounds
beam polarization
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Key Ingredients

• High beam polarization and current
• Largest LH2 target in the world
• Spectrometer optimized for Møller kinematics
• Stringent control of helicity-dependent
  systematics

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Liquid Hydrogen Target
Refrigeration Capacity 1 kW Operating
Temperature 20 K Length
1.5 m Flow Rate 5
m/s Vertical Motion 6 inches
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Beam Diagnostics
Energy dithering region
A-Line
linac
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Kinematics
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Detector Concept
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MOLLER Detector
electron flux
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Profile Detector

• 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
• Q2 measurement

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Scattered Flux Profile
Møller peak scan data vs Monte Carlo
Møller scattering kinematics ltQ2gt 0.0266
GeV-2 ltygt 0.6
Data Monte Carlo

• 2 mm geometry
• 1 energy scale
• Radiative tail
• lt1 background

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MOLLER Statistics and Fluctuations
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Physics Runs
Energy days _at_120Hz Peta-Electron spills Average Charge Production Efficiency
Run I 45.6 GeV 19.2 67K 125M 5.5 x 1011 63
Run I 48.8 GeV 14.8 37K 105M 3.5 x 1011 69
Run II 45.6 GeV 15.2 56K 113M 5.2 x 1011 72
Run II 48.8 GeV 19.0 63K 153M 4.3 x 1011 78
Efficiency is avg. delivered rate normalized to
119Hz
1020 Electrons on Target
Run I April 23 1200 May 28 0000 (this
result) Run II October 10 0800 November 13
1600
Run 2 Run 1

• 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

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Raw Asymmetry Statistics
Asymmetry pulls per pulse pair
Asymmetry pulls per run
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ep Detector Data
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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
• 3510 ppb correction to Møller asymmetry in Run
  I, below
• 20 ppb for Run II

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Corrections and Backgrounds

• Conservative Run I systematic error estimates
  working to reduce
• Run I systematic error from 24 to less than 15
  ppb
• Run II corrections will be of order 25 ppb

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Normalization Errors
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Møller Asymmetry vs Slug
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Grand Averages
APV(e-e- at Q2 0.027 GeV2) -151.9 ? 29.0
(stat) ? 32.5 (syst) parts per billion (preliminar
y)
Significance of parity violation in Møller
scattering 3.6 ?
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The Weak Mixing Angle

• sin2?eff(Q20.027 GeV2) 0.2371 0.0025 (stat)
  0.0027 (syst)
• (preliminary)
• Standard Model prediction 0.2386 0.0006

Convert to for comparison
with other experiments
(preliminary)
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Implications and Outlook

• Parity is violated in Møller scattering
• Limit on ?LL at the level of 3-4 TeV (90 C.L.)
• Limits on extra Zs at the level of 400-500 GeV
• Limit on lepton-flavor violating coupling 0.02
  GF

These numbers are currently on par with collider
limits
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Outlook

• First measurement of Parity Violation in Møller
  Scattering
• Preliminary result on APV -151.9 29.0 32.5
  ppb
• sin2?eff 0.2371 0.0025 0.0027 (preliminary)
• Experiment poised to achieve proposal goals
• E158 Run II data are being analyzed, will double
  statistics
• Planning a final physics Run III July-August 2003