1 SLUO 2004SLAC E-158 A Study of Parity Violation in Møller Scattering Mike Woods, SLAC SLUO Meeting, July 2004 E158 Goal: sin 2 W = +/- 0.001 Best

SLUO 2004 SLAC E-158 1

SLAC E-158SLAC E-158A Study of Parity Violation

in Møller Scattering

Mike Woods, SLAC

SLUO Meeting, July 2004

E158 Goal: sin2W = +/- 0.001Best measurement of W away from the Z-pole


For E158, E=48 GeV, Q2=0.03 GeV2

At tree level, APV= -3 x 10-7

PVemeasPV

WPV

LR

LRPV

APA

A

A

)sin41( 2

For a polarized electron beam and an unpolarized electron target,

Parity Violation in Moller ScatteringParity Violation in Moller Scattering


Parity Violation,Parity Violation, Weak Mixing AngleWeak Mixing Angle

f

f

0Z )sin()'(

sin

2/

23

2/122W

ff

Wf

QIgg

gQ

g

LH coupling

)sin()'(

sin

0

22/122W

f

Wf

Qgg

gQ

RH coupling

eW

f

f

SU(2)L x U(1), with isotriplet field Ai SU(2)L coupling constant is g

and isosinglet field BU(1) coupling constant is g’

A1, A2

are charged fields and correspond to W+, W- particles A3

, B are neutral and can mix, giving the Z0 and particles Weak mixing angle: g’=g tanW

Electroweak Theory:


Parity Violation at Low QParity Violation at Low Q22

-Z interference)

• first observation of PV in weak neutral scattering • cornerstone experiment that solidified the Standard Model developed by Glashow, Weinberg and Salam

Studies pioneered by SLAC E-122 (lepton-nucleon DIS):

020.0224.0sin2 W(APV ~ 10-4)


Parity Violation at the Z-poleParity Violation at the Z-pole

22

2

sin411

sin412eff

W

effW

RL

RLLRPV AA

0Z

e

e

f

f

Very precise measurements by SLD at SLAC

• best measurement of weak mixing angle best indirect constraint on the Higgs mass

00026.023098.0sin 22 Zeff

W M(APV ~ -0.15)


Electroweak MeasurementsElectroweak Measurementsaway from the Z-poleaway from the Z-pole

E-158 probes TeV-scale physics: contact interactions, LL ~ 10 TeVZ’ ~ 1 TeV


Low QLow Q22 Measurements of Measurements of WW

Purely leptonic reaction gee ~ 1 - 4sin2W


SLAC E-158SLAC E-158

2 GHz45 GeV

P=85%

5x1011 e-/pulse

L ~ 1038 cm-2s-1 integratingflux counter

LH24-7 mrad

End Station AEnd Station A


•UC Berkeley•Caltech•Jefferson Lab•Princeton•Saclay

•SLAC•Smith College•Syracuse•UMass•Virginia

7 Ph.D. Students60 physicists

Sep 97: EPAC approval1998-99: Design and Beam Tests2000: Funding and construction2001: Engineering run2002: Physics Runs 1 (Spring), 2 (Fall)2003: Physics Run 3 (Summer)

E158 CollaborationE158 Collaboration

SLUO 2004 SLAC E-158 10

Key Ingredients

• High beam polarization and current• Largest high-power LH2 target in the world• Spectrometer optimized for Møller

kinematics • Stringent control of helicity-dependent

systematics. Passive asymmetry reversals

SLUO 2004 SLAC E-158 11

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 85-90% 80%

Train Length 270ns 267ns

Microbunch spacing 0.3ns 1.4ns

Beam Loading 13% 22%

Energy Spread 0.15% 0.3%

E-158 BeamE-158 Beam(and comparison with 500 GeV Linear Collider Design)

E-158 profited considerably from the photocathode R&D carried out for NLC

(gradient-doped strained superlattice cathode in Run 3 had P~90%!)

SLUO 2004 SLAC E-158 12

Can compare measurements of neighboring devices to determine the precision of the measurement.

Energy dithering region

BPM ~2 micronsenergy ~1 MeV

Agreement (MeV)

BPM

24

X (

MeV

)

BPM12 X (MeV)

toroid ~30 ppm

Beam Monitoring DevicesBeam Monitoring Devices

SLUO 2004 SLAC E-158 13

End Station A

SLUO 2004 SLAC E-158 14

Scattering Chamber and Spectrometer Magnets

LH2 Scattering Chamber

‘Sewer Pipe’ in front of Detector Cart

SLUO 2004 SLAC E-158 15

MOLLER, ep are (copper/fused silica fiber) calorimetersPION is a quartz bar CherenkovLUMI is an ion chamber with Al pre-radiator

4

1

EMOLLER

42

1

EMOTT

mrad

mrad

MOLLERlab

LUMIlab

0.6

5.1

All detectors have azymuthal segmentation, and have PMT readout to 16-bit ADC

DetectorsDetectors

SLUO 2004 SLAC E-158 16

ep Background to Moller sample:• 6% from elastic scattering• 1% from inelastic scattering• (30±6) ppb correction

QC1B (main acceptance) collimator

Insertable QC1A collimator- used for polarimetry

Scattered Flux ProfileScattered Flux Profile

ee Moller signal

ep

Moller Detector ep Detector

SLUO 2004 SLAC E-158 17

Experimental FeaturesExperimental Features

Beam helicity is chosen pseudo-randomly at 120 Hz• use electo-optical Pockels cell in Polarized Light Source• sequence of pulse quadruplets; one quadruplet every 33 ms: 43432121 RRRRRRRR

Also, False Asymmetry Reversals: (reverse false beam position and angle asymmetries; physics asymmetry unchanged)

• 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 Moller scattering

Physics Asymmetry Reversals:• Insertable Halfwave Plate in Polarized Light Source• (g-2) spin precession in A-line (45 GeV and 48 GeV data)

SLUO 2004 SLAC E-158 18

AAPV PV MeasurementMeasurement1. Measure asymmetry for each pair of pulses, p,

LR

LRpexp σ σ

σ -σ A

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

iipexp

praw ΔxaAA

3. Sum over all pulse pairs, prawraw AA

bkg

bkgraw

bPV f

AA

P

1A

4. Obtain physics asymmetry:

backgrounds

beam polarization, linearitybackground dilutions

SLUO 2004 SLAC E-158 19

Observe ~ 2.5 ppm asymmetryFirst measurement of single-spin

transverse asymmetry in e-e scattering.

Flips sign at 43 GeV

Asymmetry vs

Two-photon exchange; QED measurement with E-158

Theory References: 1. A. O. Barut and C. Fronsdal, (1960) 2. L. L. DeRaad, Jr. and Y. J. Ng (1975) 3. Lance Dixon and Marc Schreiber; hep-ph/0402221

(Raw) Transverse ee Asymmetry Transverse ee Asymmetry

i) Interesting signal, ii) potential background for APV measurementiii) Studying its utility for calibration of polarization scale

SLUO 2004 SLAC E-158 20

• Has opposite sign • elastic ep asymmetry should be negligible ~O(10-10)• ~ 25% inelastic ep• Few percent pions (asymmetry small) Proton structure and QCD at E158 !

~ 24 hrs of data

(Raw) Transverse ep Asymmetry Transverse ep Asymmetry

Asymmetry vs

SLUO 2004 SLAC E-158 21

ep Detector Data ep Detector Data (Run 1)(Run 1)

Ratio of asymmetries:APV(48 GeV) /APV(45 GeV) = 1.25 ± 0.08 (stat) ± 0.03 (syst)

ARAW(45 GeV) = -1.36 ± 0.05 ppm (stat. only)ARAW(48 GeV) = -1.70 ± 0.08 ppm (stat. only)

Consistent with expectations for inelastic ep asymmetry

SLUO 2004 SLAC E-158 22

,1

f

AA

εPA raw

bPV

Source A (ppb) f

Beam asymmetries (-) ± 4 -

Beam spotsize 0 ± 1 -

Transverse polarization -4 ± 2 -

ep elastic -8 ± 2 0.058 ± 0.007

ep inelastic -22 ± 6 0.009 ± 0.003

Brem and Compton electrons 0 ± 1 0.005 ± 0.002

Pions 1 ± 1 0.001 ± 0.001

High energy photons 3 ± 3 0.004 ± 0.002

Synchrotron photons 0 ± 2 0.0015 ± 0.0005

Neutrons -1 ± 1 0.0006 ± 0.0002

TOTAL -31 ± 8 0.079 ± 0.009

AAPVPV Corrections, Corrections, A, and dilution factors, fA, and dilution factors, f

01.099.0linearity

05.088.0

bP

*Beam polarization measured using polarized foil target; same spectrometer used with dedicated movable detector

SLUO 2004 SLAC E-158 23

Run I Results Published

SLUO 2004 SLAC E-158 24

APV(e-e- at Q2 = 0.026 GeV2): -128 14 (stat) 12 (syst) parts per billion (preliminary)

Significance of parity nonconservation in Møller scattering: 8

Moller Asymmetry, APVMoller Asymmetry, APV

SLUO 2004 SLAC E-158 25

from Afrom APVPV to sin to sin22WWeffeff

eff

WbremF

PV Fyy

yQGA

2

44

2

sin4111

1

24

where:

44

2

11

1

24 yy

yQGF

is an analyzing power factor; depends on kinematics and experimental geometry. Uncertainty is 1.7%. (y = Q2/s)

Fbrem = (1.016 ± 0.005) is a correction for ISR and FSR; (but thick target ISR and FSR effects are included in the analyzing power calculation from a detailed MonteCarlo study)

Weff is derived from an effective coupling constant, gee

eff , for the Zee coupling,with loop and vertex electroweak corrections absorbed into gee

eff

SLUO 2004 SLAC E-158 26

E158 Weak Mixing Angle ResultE158 Weak Mixing Angle Result

QQ22-dependence of -dependence of WW

7

SLUO 2004 SLAC E-158 27

Summary: Physics results from E-158Summary: Physics results from E-158Electro-weak parity violation

• first observation of parity violation in Møller scattering (8)• running of the weak mixing angle established (7 )• Probing TeV-scale physics: ~10 TeV limit on LL,

~900 GeV limit on SO(10) Z’• inelastic e-p asymmetry consistent with quark picture

Transverse asymmetries• First measurement of e-e transverse asymmetry (QED)• e-p transverse asymmetry measured (QCD)

Weak Mixing AngleWeak Mixing Angle

Preliminary Results using all dataAPV (Moller) = (-128 ± 14 ±12) ppb

sin2WMS(MZ

2)= 0.2330 ± 0.0011 (stat) ±0.0010 (syst) Best measurement of the weak mixing angle

away from the Z-pole!

Documents

1 SLUO 2004SLAC E-158 A Study of Parity Violation in Møller Scattering Mike Woods, SLAC SLUO Meeting, July 2004 E158 Goal: sin 2 W = +/- 0.001 Best