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The Qpweak Experiment:

A Search for Physics beyond the Standard Model

via parity-violating e-p scattering at low Q2

S. Page, PAVIO6, Milos, Greece

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Parity violating scattering asymmetry

MEMMNC

Interference givesparity violating scattering asymmetry for polarized beam

ep

( )s

ep

( )s

2Q 0

20 2 4Q Q

2

4 2Q

N

pwe

C

EM

Fak

Md dA

d d M

GB Q

“hadronic form factor” correction

Q2 Dependence: this morning’stalks

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What is the proton’s weak charge and why are we measuring it?

QpWeak = 1 – 4sin2 θW , which has never been

directly measured in a precision experiment, sets the scale of the proton’s coupling to W and Z bosonsthat mediate the weak interaction:

• The weak mixing angle, sin2 θW, is predicted to vary with the energy scale (Q)

at which it is measured, due to electroweak radiative corrections that aresensitive to the possible existence of additional force carriers beyond the Standard Model -- e.g. right handed Z bosons etc.

• sin2 θW is well determined at the Z-pole from high energy collider experiments but lower energy precision measurements have not yet been made

• The Qweak experiment at Jefferson Lab will enable us to check the predicted “running” of sin2 θW, by making a precision measurement at low energy, placing limits on physics beyond the Standard Model.

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Energy Scale dependence of the weak mixing angle:

Significance: planned error bar corresponds to a 10 measurement of the Standard Model prediction

0.001 0.01 0.1 1 10 100 1000

Q [GeV]

0.225

0.23

0.235

0.24

0.245

0.25

APV

QW(p)eD-DIS

QW(e) -DIS

AFB

Z-pole

current

future

SM

Standard Model PredictionErler, Kurylov & Ramsey-Musolf,Phys. Rev. D 68, 016006 (2003)

SLAC E158

Cs atomic parity violation

NuTeV

Qweak goal error bar

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JLab Qweak

(proposed)-

• Qweak measurement will provide a stringent stand alone constraint

on Lepto-quark based extensions to the SM.

• Qpweak (semi-leptonic) and E158 (pure leptonic) together make a

powerful program to search for and identify new physics.

SLAC E158

Comparison of proton and electron weak charge sensitivities

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Impact via “Model-independent Semi-Leptonic Analysis”

Effective electron-quark neutralcurrent Lagrangian:

Large ellipse (existing data):SLAC e-D (DIS)MIT-Bates 12C (elastic)Cesium atomic parity violation

Red ellipse:Impact of Qp

Weak measurement(centroid assumes agreementwith the Standard Model)

C1u C1u(exp) C1u(SM)C1d C1d(exp) C1d(SM)

Le-qPV

GF

2e e C1qq q

q

A(e) x V(q)

Erler, Kurylov & Ramsey-Musolf: Phys.Rev.D68:016006,2003

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Experimental sensitivity: 072.0)sin41( 2 Wp

WQ

%3.0)(sin%4 2 Wp

WQ Precision measurement:

2 4 22 Q( 0 Q)2

Q4

pweak

FGA Q B Q

Physics Asymmetry:

2(Q

ppm

)

p

2

pm

GeV(0.03 )

.19 .10

pW B QA A A

Expected value:

Experimental considerations:• need high statistics integrating detector system

• measured asymmetry is P A beam polarization P should be large & well measured• somebody else has to measure B(Q2) for us (done ) so that we can subtract it• we need to know the detector-response-weighted <Q2> and <Q4> to interpret the data• helicity correlated systematic errors must be kept below 5 x 10-9

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Anticipated QpWeak Uncertainties

Aphys /Aphys Qpweak/Qp

weak

Statistical (2200 hours production) 1.8% 2.9%Systematic:

Hadronic structure uncertainties -- 2.2% Beam polarimetry 1.0% 1.6% Absolute Q2 determination 0.7% 1.1% Backgrounds 0.5% 0.8% Helicity-correlated Beam Properties 0.5% 0.8%_________________________________________________________ Total 2.3% 4.3%

Aphys /Aphys Qpweak/Qp

weak

Statistical (2200 hours production) 1.8% 2.9%Systematic:

Hadronic structure uncertainties -- 2.2% Beam polarimetry 1.0% 1.6% Absolute Q2 determination 0.7% 1.1% Backgrounds 0.5% 0.8% Helicity-correlated Beam Properties 0.5% 0.8%_________________________________________________________ Total 2.3% 4.3%

An additional uncertainty associated with QCD corrections applied to the extraction of sin2W : it raises sin2W / sin2W from 0.2% to 0.3%.

An additional uncertainty associated with QCD corrections applied to the extraction of sin2W : it raises sin2W / sin2W from 0.2% to 0.3%.

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Hadronic Form Factors

A AQW

p Ahadronic Aaxial

.19 ppm .09 ppm .01 ppm

A AQW

p Ahadronic Aaxial

.19 ppm .09 ppm .01 ppm

hadronic: (31% of asymmetry) - contains GE,M GZ

E,M

Constrained by HAPPEX, G0, MAMI PVA4

hadronic: (31% of asymmetry) - contains GE,M GZ

E,M

Constrained by HAPPEX, G0, MAMI PVA4

axial: (4% of asymmetry) -

contains GeA,

has large electroweak radiative corrections.

Constrained by G0 and SAMPLE

axial: (4% of asymmetry) -

contains GeA,

has large electroweak radiative corrections.

Constrained by G0 and SAMPLE Young et al., arXiv:nucl-ex/0604010

Hadronic FF’s at Q2 = 0.1 GeV2 extrapolationto Q2 = 0.03 GeV2 gives contribution to Qweak

(see Ross Young’s talk !)

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~

close

ontrack85%

85 – 87 %Achieved at injector

Beam Property Requirements

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Main apparatus: target plus toroidal magnetic spectrometer

beam

double collimatorsystem selectsscattering angle/accepted Q2 range

toroidal magnetic spectrometer:elastically scattered electronsare bent away from the beamlineand focused onto the detector plane

photons hit here

inelastic electrons

quartz detectorsfor elastic e-

LH2 target

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Qweak LH2 target

• 2500 W cooling power !• raster size 4 x 4 mm2

• / < 10 ppm @ 30 Hz

Requirements:

Noise spectra measured in Hall A -- great improvement at higher spin flip frequency

(up to 250 Hz implemented at the polarized source already)solid target

liquid target

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Region 3: Vertical Drift chambers

Region 2: Horizontal drift chamber locationRegion 1: GEM

Gas Electron Multiplier

Quartz Cerenkov Bars(insensitive to non-relativistic particles)

Collimator System

Mini-torus

QTOR Magnet

Trigger Scintillator

Lumi Monitors

e- beam

Ebeam = 1.165 GeVIbeam = 180 μAPolarization ~85%Target = 2.5 kW

Layout drawing: main asymmetry

(We will turn down the beam current and track particles to determine <Q2>, <Q4>)

plus tracking apparatus for <Q2>, <Q4>

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View of QpWeak Apparatus collapsed along beam direction - Simulated Events

Central scattering angle: ~8° ± 2Phi Acceptance: > 50% of 2Average Q²: 0.027 GeV2

Acceptance averaged asymmetry: –0.29 ppmIntegrated Rate (per detector): ~900 MHzInelastic/Elastic ratio: ~0.01%

Central scattering angle: ~8° ± 2Phi Acceptance: > 50% of 2Average Q²: 0.027 GeV2

Acceptance averaged asymmetry: –0.29 ppmIntegrated Rate (per detector): ~900 MHzInelastic/Elastic ratio: ~0.01%

Elastic e-p envelope

close up: distribution across top detector bar

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Main Detector and Electronics System

Focal plane detector requirements:

• Insensitivity to background , n, .• Radiation hardness (expect > 300 kRad).• Operation at ~ counting statistics• nonlinearity less than 1%

Fused Silica (synthetic quartz) Cerenkov detector.

• Plan to use 18 cm x 200 cm x 1.25 cm quartz • bars read out at both ends by S20 photocathode PMTs (expect ~ 50 pe/event)• n =1.47, Cerenkov=47°, total internal reflection tir=43°• reflectivity = 0.997

Electronics (LANL/TRIUMF design):

• Normally operates in integration mode.• Will have connection for pulse mode.• Low electronic noise contribution.

compared to counting statistics.• 18 bit ADC will allow for 4X over sampling

Op Amp

1 M 2 pF

Fiber Optic

Converter

15 V

1 MHz 16 bit ADC

110 VAC in Pulse mode in

10 k

PMT HV in

PMT anode

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Determination of Average Q2

~10 nA e- beam

Region 1: GEMGas Electron Multiplier

Region 2 : 2 Horizontal Drift chambers

Region 3: 2 Vertical Drift chambers

Shielding wall

Quartz Cerenkov bar

distribution:<Q2> = 0.03 GeV2

• reduce beam current• use tracking system• read out quartz light yield

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Precision Polarimetry

• Present limitations – existing Moller polarimeter- IMax ~ 10 A.

- At higher currents the Fe

target depolarizes.- Measurement is destructive

• Møller upgrade:- Measure Pbeam at 100 A or

higher, quasi-continuously- Trick: kicker + strip or wire

target

• Schematic of planned new Hall C Compton polarimeter.

Q2

D2

Q1

D3

D1D=0.52 m

1 m2 m 1.5 m

9.5 m

Electron detector

D4

PhotonDetector

Existing Hall C Møller can achieve 1% (statistics) in a few minutes.

See talks on Saturday:• Jurgen Diefenbach (Compton)• Dave Mack (Moller)

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Summary and Outlook

• We will measure the proton’s weak charge, QWp to 4% and hence determine

sin2W to 0.3% from low Q2 parity-violating elastic scattering at Jefferson Lab.

• Experiment approved with “A” rating, 2002 & reaffirmed 2005

• JLab schedule: installation in 2009 and 18 months on the floor before 12 GeV upgrade

• Progress on experiment design, simulations, prototyping and construction is underway:

magnet coils at MIT support stand

19Region 1 GEM prototype

chamber rotator

Rad Hard preamp

collaboration meeting

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Qweak Collaboration Spokespersons

Carlini, Roger (Principal Investigator) - Thomas Jefferson National Accelerator FacilityFinn, J. Michael - College of William and MaryKowalski, Stanley - Massachusetts Institute of TechnologyPage, Shelley - University of Manitoba

Qweak Collaboration Members

Armstrong, David - College of William and MaryAverett, Todd - College of William and MaryBirchall, James - University of ManitobaBosted, Peter – Thomas Jefferson National Accelerator FacilityBotto, Tancredi - Massachusetts Institute of TechnologyBowman, David – Los Alamos National LaboratoryBruell, Antje - Thomas Jefferson National Accelerator FacilityCates, Gordon – University of VirginiaChattopadhyay, Swapan - Thomas Jefferson National Accelerator FacilityDavis, Charles - TRIUMFDoornbos, J. - TRIUMFDow, Karen - Massachusetts Institute of TechnologyDunne, James - Mississippi State UniversityEnt, Rolf - Thomas Jefferson National Accelerator FacilityErler, Jens - University of MexicoFalk, Willie - University of ManitobaFarkhondeh, Manouchehr - Massachusetts Institute of TechnologyForest, Tony - Louisiana Tech UniversityFranklin, Wilbur - Massachusetts Institute of TechnologyGaskell, David - Thomas Jefferson National Accelerator FacilityGericke, Michael – University of Manitoba and TRIUMFGrimm, Klaus - College of William and MaryHersman, F. W. - University of New HampshireHoltrop, Maurik - University of New HampshireJohnston, Kathleen - Louisiana Tech UniversityJones, Richard - University of ConnecticutJoo, Kyungseon - University of Connecticut

Keppel, Cynthia - Hampton UniversityKhol, Michael - Massachusetts Institute of TechnologyKorkmaz, Elie - University of Northern British Columbia Lee, Lawrence - TRIUMFLiang, Yongguang - Ohio UniversityLung, Allison - Thomas Jefferson National Accelerator FacilityMack, David - Thomas Jefferson National Accelerator FacilityMajewski, Stanislaw - Thomas Jefferson National AcceleratorMammei, Juliette - Virginia Polytechnic Inst. & State Univ.Mammei, Russell - Virginia Polytechnic Inst. & State Univ.Martin, Jeffery W. – University of WinnipegMeekins, David – Thomas Jefferson National Accelerator FacilityMkrtchyan, Hamlet - Yerevan Physics InstituteMorgan, Norman - Virginia Polytechnic Inst. & State Univ.Myers, Catherine – George Washington UniversityOpper, Allena – George Washington Univ.Penttila, Seppo - Los Alamos National LaboratoryPitt, Mark - Virginia Polytechnic Inst. & State Univ.Poelker, B. (Matt) - Thomas Jefferson National Accelerator FacilityProk, Yelena – Massachusetts Institute of TechnologyRamsay, Des - University of Manitoba and TRIUMFRamsey-Musolf, Michael - California Institute of TechnologyRoche, Julie - Thomas Jefferson National Accelerator FacilitySimicevic, Neven - Louisiana Tech UniversitySmith, Gregory - Thomas Jefferson National Accelerator FacilitySmith, Timothy - Dartmouth CollegeSouder, Paul –Syracuse UniversitySuleiman, Riad – Virginia Polytechnic & State Univ.Tsentalovich, Evgeni - Massachusetts Institute of Technologyvan Oers, W.T.H. - University of ManitobaWang, Jie Pan – University of WinnipegWang, Peiqing – University of ManitobaWells, Steven - Louisiana Tech UniversityWood, Stephen Thomas - Jefferson National Accelerator FacilityZhu, Hongguo - University of New HampshireZiskin, Vitaly – MIT Bates Linear Accelerator LaboratoryZorn, Carl - Thomas Jefferson National Accelerator FacilityZwart, Townsend - Massachusetts Institute of Technology

The Qweak Collaboration: www.jlab.org/qweak/

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The Qpweak Luminosity Monitor

• Luminosity monitor Symmetric array of 8 quartz Cerenkov detectors instrument with rad hard vacuum photo diodes

& integrating readout at small (~ 1.2). Low Q2, high rates ~29 GHz/octant.

• Expected signal components: 12 GHz e-e Moeller, 11 GHz e-p elastic, EM showers 6 GHz. • Expected lumi monitor asymmetry << main detector asymmetry.• Expected lumi monitor statistical error ~ (1/6) main detector statistical error.

• Useful for:

Sensitive check on helicity-correlated beam parameter corrections procedure.

Regress out target density fluctuations.

MAMI A4 “LUMI” Monitor

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