The Q p weak Experiment: A Search for Physics beyond the Standard Model

1. 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

2. Interference gives parity violating scattering asymmetry for polarized beam MNC MEM this morning’s talks  “hadronic form factor” correction Parity violating scattering asymmetry Q2 Dependence:

3. 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 bosons that 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 are sensitive 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.

4. Qweak goal error bar SLAC E158 NuTeV Cs atomic parity violation Standard Model Prediction Erler, Kurylov & Ramsey-Musolf, Phys. Rev. D 68, 016006 (2003) Energy Scale dependence of the weak mixing angle: Significance: planned error bar corresponds to a 10 measurement of the Standard Model prediction

5. Comparison of proton and electron weak charge sensitivities JLab Qweak SLAC E158 - (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.

6. Impact via “Model-independent Semi-Leptonic Analysis” Effective electron-quark neutral current Lagrangian: DC1u  C1u(exp) C1u(SM) DC1d  C1d(exp) C1d(SM) Large ellipse (existing data): SLAC e-D (DIS) MIT-Bates 12C (elastic) Cesium atomic parity violation Red ellipse: Impact of QpWeak measurement (centroid assumes agreement with the Standard Model) Erler, Kurylov & Ramsey-Musolf: Phys.Rev.D68:016006,2003

7. Precision measurement: Physics Asymmetry: Expected value: Experimental sensitivity: • 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

8. Anticipated QpWeak Uncertainties  Aphys/AphysQpweak/Qpweak 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 sin2W : it raises sin2W / sin2W from 0.2% to 0.3%.

9. hadronic: (31% of asymmetry) - contains GE,M GZE,M Constrained by HAPPEX, G0, MAMI PVA4 axial: (4% of asymmetry) - contains GeA, has large electroweak radiative corrections. Constrained by G0 and SAMPLE Young et al., arXiv:nucl-ex/0604010 Hadronic Form Factors Hadronic FF’s at Q2 = 0.1 GeV2 extrapolation to Q2 = 0.03 GeV2 gives contribution to Qweak (see Ross Young’s talk !)

10. Beam Property Requirements ~    close on track 85% 85 – 87 % Achieved at injector

11. Main apparatus: target plus toroidal magnetic spectrometer inelastic electrons quartz detectors for elastic e- LH2 target photons hit here beam double collimator system selects scattering angle/ accepted Q2 range toroidal magnetic spectrometer: elastically scattered electrons are bent away from the beamline and focused onto the detector plane

12. liquid target 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 Qweak LH2 target Requirements: • 2500 W cooling power ! • raster size 4 x 4 mm2 • / < 10 ppm @ 30 Hz

13. Layout drawing: main asymmetry plus tracking apparatus for <Q2>, <Q4> Quartz Cerenkov Bars (insensitive to non-relativistic particles) Region 2: Horizontal drift chamber location Region 1: GEM Gas Electron Multiplier Mini-torus e- beam Ebeam = 1.165 GeV Ibeam = 180 μA Polarization ~85% Target = 2.5 kW Lumi Monitors QTOR Magnet Region 3:Vertical Drift chambers Collimator System Trigger Scintillator (We will turn down the beam current and track particles to determine <Q2>, <Q4>)

14. close up: distribution across top detector bar View of QpWeak Apparatus collapsed along beam direction - Simulated Events Central scattering angle: ~8° ± 2 Phi Acceptance: > 50% of 2 Average Q²: 0.027 GeV2 Acceptance averaged asymmetry: –0.29 ppm Integrated Rate (per detector): ~900 MHz Inelastic/Elastic ratio: ~0.01% Elastic e-p envelope

15. 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 MainDetector 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

16. Quartz Cerenkov bar Region 3: 2 Vertical Drift chambers ~10 nA e- beam Shielding wall Region 2 : 2 Horizontal Drift chambers Region 1: GEM Gas Electron Multiplier Determination of Average Q2 distribution: <Q2> = 0.03 GeV2 • reduce beam current • use tracking system • read out quartz light yield

17. See talks on Saturday: • Jurgen Diefenbach (Compton) • Dave Mack (Moller) 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. Existing Hall C Møller can achieve 1% (statistics) in a few minutes.

18. magnet coils at MIT support stand Summary and Outlook • We will measure the proton’s weak charge, QWp to  4% and hence determine • sin2W 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:

19. collaboration meeting chamber rotator Rad Hard preamp Region 1 GEM prototype

20. The Qweak Collaboration: www.jlab.org/qweak/ Keppel, Cynthia - Hampton University Khol, Michael - Massachusetts Institute of Technology Korkmaz, Elie - University of Northern British Columbia Lee, Lawrence - TRIUMF Liang, Yongguang - Ohio University Lung, Allison - Thomas Jefferson National Accelerator Facility Mack, David - Thomas Jefferson National Accelerator Facility Majewski, Stanislaw - Thomas Jefferson National Accelerator Mammei, Juliette - Virginia Polytechnic Inst. & State Univ. Mammei, Russell - Virginia Polytechnic Inst. & State Univ. Martin, Jeffery W. – University of Winnipeg Meekins, David – Thomas Jefferson National Accelerator Facility Mkrtchyan, Hamlet - Yerevan Physics Institute Morgan, Norman - Virginia Polytechnic Inst. & State Univ. Myers, Catherine – George Washington University Opper, Allena – George Washington Univ. Penttila, Seppo - Los Alamos National Laboratory Pitt, Mark - Virginia Polytechnic Inst. & State Univ. Poelker, B. (Matt) - Thomas Jefferson National Accelerator Facility Prok, Yelena – Massachusetts Institute of Technology Ramsay, Des - University of Manitoba and TRIUMF Ramsey-Musolf, Michael - California Institute of Technology Roche, Julie - Thomas Jefferson National Accelerator Facility Simicevic, Neven - Louisiana Tech University Smith, Gregory - Thomas Jefferson National Accelerator Facility Smith, Timothy - Dartmouth College Souder, Paul –Syracuse University Suleiman, Riad – Virginia Polytechnic & State Univ. Tsentalovich, Evgeni - Massachusetts Institute of Technology van Oers, W.T.H. - University of Manitoba Wang, Jie Pan – University of Winnipeg Wang, Peiqing – University of Manitoba Wells, Steven - Louisiana Tech University Wood, Stephen Thomas - Jefferson National Accelerator Facility Zhu, Hongguo - University of New Hampshire Ziskin, Vitaly – MIT Bates Linear Accelerator Laboratory Zorn, Carl - Thomas Jefferson National Accelerator Facility Zwart, Townsend - Massachusetts Institute of Technology Qweak Collaboration Spokespersons Carlini, Roger (Principal Investigator) - Thomas Jefferson National Accelerator Facility Finn, J. Michael - College of William and Mary Kowalski, Stanley - Massachusetts Institute of Technology Page, Shelley - University of Manitoba Qweak Collaboration Members Armstrong, David - College of William and Mary Averett, Todd - College of William and Mary Birchall, James - University of Manitoba Bosted, Peter – Thomas Jefferson National Accelerator Facility Botto, Tancredi - Massachusetts Institute of Technology Bowman, David – Los Alamos National Laboratory Bruell, Antje - Thomas Jefferson National Accelerator Facility Cates, Gordon – University of Virginia Chattopadhyay, Swapan - Thomas Jefferson National Accelerator Facility Davis, Charles - TRIUMF Doornbos, J. - TRIUMF Dow, Karen - Massachusetts Institute of Technology Dunne, James - Mississippi State University Ent, Rolf - Thomas Jefferson National Accelerator Facility Erler, Jens - University of Mexico Falk, Willie - University of Manitoba Farkhondeh, Manouchehr - Massachusetts Institute of Technology Forest, Tony - Louisiana Tech University Franklin, Wilbur - Massachusetts Institute of Technology Gaskell, David - Thomas Jefferson National Accelerator Facility Gericke, Michael – University of Manitoba and TRIUMF Grimm, Klaus - College of William and Mary Hersman, F. W. - University of New Hampshire Holtrop, Maurik - University of New Hampshire Johnston, Kathleen - Louisiana Tech University Jones, Richard - University of Connecticut Joo, Kyungseon - University of Connecticut

22. 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 Similar to