The Q p weak Experiment – A Search for New Physics at the TeV Scale

1. The Qpweak Experiment – A Search for New Physics at the TeV Scale Mark Pitt Virginia Tech • Brief review of recent and planned low energy neutral • current Standard Model tests • Overview and status report of an approved JLAB • Standard Model test – The Qpweak Experiment • Brief review of most recent results on strange electric • and magnetic form factors of the nucleon

2. Running coupling constants in QED and QCD QCD(running of s) QED (running of ) 137  s What about the running of sin2W?

3. +  + “Running of sin2W” in the Electroweak Standard Model • Electroweak radiative corrections •  sin2W varies with Q • All “extracted” values of sin2W must agree with the Standard • Model prediction or new physics is indicated.

4. Why are Precision Measurements far Below the Z-pole Sensitive to New Physics? Precision measurements well below the Z-pole have more sensitivity (for a given experimental precision) to new types of tree level physics, such as additional heavier Z’ bosons.

5. Low Energy Weak Neutral Current Standard Model Tests Low energy weak charge “triad” (M. Ramsey-Musolf) probed in weak neutral current experiments SLAC E158: parity-violating Moller scattering e + e  e + e Cesium Atomic Parity Violation: primarily sensitive to neutron weak charge JLAB Qpweak: parity-violating e-p elastic scattering e + p  e + p These three types of experiments are a complementary set for exploring new physics possibilities well below the Z pole.

6. Qeweak : Electron Weak Charge – SLAC E158 Experiment e + e  e + e Parity-violating Moller scattering Q2 ~ .026 GeV2  ~ 4 – 7 mrad E ~ 48 GeV at SLAC End Station A Final results: hep-ex/0504049 APV = -131  14 (stat)  10 (syst) ppb sin2eff(Q2=0.026 GeV2) =0.2397 ± 0.0010 ±0.0008 Running of sin2eff established at 6 level in pure leptonic sector

7. Atomic Parity Violation in the Cesium Atom (B x E)s • Boulder 133Cs experiment (Wood et al., Science 275, 1759 (1997)): • Measures modification of neutral weak current to the S-P Stark mixing in an applied electric field • Isolate the parity non-conserving piece (PNC) with five different reversals PNC expt. + atomic theory: QW(133Cs) = -72.84 ± (0.29)expt ± (0.36)theor Standard Model prediction: QW(133Cs) = -73.09 ± (0.03) after a turbulent 2-year period as the atomic theory was successively improved.

8. Future Directions for PV Moller and APV e2ePV: Parity-Violating Moller scattering at 12 GeV JLAB (Mack, Reimer, et al.) • Achieve Moller focus with long, narrow superconducting toroidal magnet, • Radiation hard detector package • E = 12 GeV Q2 =.008 GeV2 , •  ~ .53 - .92o , APV = - 40 ppb • In 4000 hours, could determine QeW to 2.5% • (compare to 12.4% for E158) Atomic Parity Violation Future Directions • Paris group (Bouchiat, et al.): more precise Cs APV • Seattle group (Fortson, et al.): single trapped Ba+ APV 6S1/2 5D3/2 • Berkeley group (Budker, et al.): isotope ratios in Yb APV • Stony Brook/Maryland group (Orozco, et al.): isotope ratios in Fr APV Note: isotope ratios can eliminate large atomic structure theory uncertainties

9. Potential of e2ePV: Parity-Violating Moller at 12 GeV JLAB A 12 GeV Moller experiment could be comparable to the world’s best weak mixing angle measurements at the Z pole (~ 0.1%).

10. “Running of sin2W” : Current Status and Future Prospects present: “d-quark dominated” : Cesium APV (QAW): SM running verified at ~ 4 level “pure lepton”: SLAC E158 (QeW ): SM running verified at ~ 6 level future: “u-quark dominated” : Qweak (QpW): projected to test SM running at ~ 10 level “pure lepton”:12 GeV e2ePV (QeW ): projected to test SM running at ~ 25  level

11. The Qpweak Experiment: A Search for New TeV Scale Physics via a Measurement of the Proton’s Weak Charge Measure:Parity-violating asymmetry in e + p elastic scattering at Q2 ~ 0.03 GeV2 to ~4% relative accuracy at JLab Extract:Proton’s weak charge Qpweak ~ 1 – 4 sin2W to get ~0.3% on sin2W at Q2 ~ 0.03 GeV2 tests “running of sin2W”from M2Z to low Q2 sensitive to new TeV scale physics

12. The QpWeak Experiment JLAB E02-020: “A Search for new physics beyond the Standard Model at the TeV Scale” The Institutions JLab, LANL, MIT, TRIUMF, William & Mary, Univ. of Manitoba, Virginia Tech, Louisiana Tech, Univ. of Connecticut, Univ. Nacional Autonoma de Mexico, Univ. of Northern British Columbia, Univ. of New Hampshire, Ohio Univ., Mississippi State, Hampton Univ., Yerevan Physics Institute The Collaboration D. Armstrong, T. Averett, J. Birchall, T. Botto, J. D. Bowman, P. Bosted, A. Bruell, R. Carlini (PI), S. Chattopadhay, C. Davis,J. Doornbos, K. Dow,J. Dunne,R. Ent,J. Erler, W. Falk, M. Farkhondeh, J.M. Finn, T. Forest, W. Franklin, D. Gaskell, K. Grimm, F. W. Hersman, M. Holtrop, K. Johnston, R. Jones, K. Joo, C. Keppel, M. Khol, E. Korkmaz, S. Kowalski, L. Lee, Y. Liang, A. Lung, D. Mack, S. Majewski, J. Martin, J. Mammei, R. Mammei,G. Mitchell, H. Mkrtchyan, N. Morgan, A. Opper, S.A. Page, S. Penttila, M. Pitt, B. (Matt) Poelker, T. Porcelli, W. Ramsay, M. Ramsey-Musolf, J. Roche, N. Simicevic, G. Smith (PM), T. Smith, R. Suleiman, S. Taylor, E. Tsentalovich, W.T.H. van Oers, S. Wells, W.S. Wilburn, S. Wood, H. Zhu, C. Zorn, T. Zwart May 2000 Collaboration formed July 2001 JLab Letter of Intent December 2001 JLab Proposal Submitted January 2002 JLab Proposal Approved with ‘A’ rating January 2003 Technical design review completed, 2003 - 2004 Funding approved by to DOE, NSF & NSERC January 2005 JLAB Jeopardy Proposal approved with ‘A’ rating

13. Jefferson Lab in Newport News, Virginia CEBAF: CW electron accelerator, energies up to 6 GeV

14. Brief History of Parity Violating Electron-Nucleon Scattering 70’s: e + d (DIS) A ~ 100 ppm SLAC E122 (Prescott, et al) Goal: measure sin2 θW = 0.22 +/- .0.02 most precise measurement at that time 80’s: e + 9Be (QE) A ~ 10 ppm Mainz e + 12C (elastic) A ~ 1 ppm MIT-Bates Goal: Standard Model test 90’s, 00’s: SAMPLE HAPPEX e + p (elastic) A ~ 2 – 50 ppm G0 MAMI PV-A4e + d (QE) Goal: Assume Standard Model is correct, measure strange form factors 00’s: Qpweak A ~ 0.3 ppm Goal: d (sin2 θW)/sin2qW ~ 0.3% at low Q2 Standard Model test

15. Qpweak is a well-defined experimental observable • Qpweak has a definite prediction in the electroweak Standard Model Qpweak: Extract from Parity-Violating Electron Scattering As Q2  0 MEM MNC measures Qp – proton’s electric charge measures Qpweak– proton’s weak charge (at tree level)

16. How to Measure the Neutral weak form factors

17. Energy Scale of an “Indirect” Search for New Physics • Parameterize New Physics contributions in electron-quark Lagrangian g: coupling constant, : mass scale • A 4% QpWeak measurement probes with • 95% confidencelevel for new physics • at energy scales to: • The TeV discovery potential of weak • charge measurements will be unmatched • until LHC turns on. • If LHC uncovers new physics, then precision • low Q2 measurements will be needed to • determine charges, coupling constants, etc.

18. Impact of QpWeak “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 APV • Red ellipse: • Impact of QpWeak measurement • (centroid assumes agreement • with standard model) • Why so much better? • precision & complementarity of QpW measurement

19. Qpweak & Qeweak – Complementary Diagnostics for New Physics JLab Qweak SLAC E158 - (proposed) Run I + II + III (preliminary) ±0.006 Erler, Kurylov, Ramsey-Musolf, PRD 68, 016006 (2003) • 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.

20. Relative Shifts in Proton and Electron Weak Charges due to SUSY Effects R parity (B-L conservation) RPC SUSY occurs only at loop level RPV SUSY occurs at tree level Erler, Ramsey-Musolf, Su hep-ph/0303026

21. Elastically Scattered Electron Luminosity Monitors Region III Drift Chambers Toroidal Magnet Region II Drift Chambers Region I GEM Detectors Eight Fused Silica (quartz) Čerenkov Detectors Collimator with 8 openings θ= 8° ± 2° 35cm Liquid Hydrogen Target Polarized Electron Beam Overview of the QpWeak Experiment Experiment Parameters (integration mode) Incident beam energy: 1.165 GeV Beam Current: 180 μA Beam Polarization: 85% LH2 target power: 2.5 KW Central scattering angle: 8.4° ± 3° Phi Acceptance: 53% of 2p Average Q²: 0.030 GeV2 Acceptance averaged asymmetry: –0.29 ppm Integrated Rate (all sectors): 6.4 GHz Integrated Rate (per detector): 800 MHz

22. Anticipated QpWeak Uncertainties  Aphys/AphysQpweak/Qpweak Statistical (2200 hours production) 1.8% 2.9% Systematic: Hadronic structure uncertainties -- 1.9% Beam polarimetry 1.0% 1.6% Absolute Q2 determination 0.5% 1.1% Backgrounds 0.5% 0.8% Helicity-correlated Beam Properties 0.5% 0.8% _________________________________________________________ Total 2.2% 4.1% 4% error on QpW corresponds to ~0.3% precision on sin2W at Q2 ~ 0.03 GeV2 (Erler, Kurylov, Ramsey-Musolf, PRD 68, 016006 (2003)) QpW = 0.0716  0.0006 theoretically 0.8% error comes from QCD uncertainties in box graphs, etc.

23. 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 Nucleon Structure Contributions to the Asymmetry Constraints on Ahadronic from other Measurements Quadrature sum of expected Ahadronic = 1.5% and Aaxial = 1.2% errors contribute ~1.9% to error on QpW

24. What role do strange quarks play in nucleon properties? proton u valence quarks u d u gluon “non-strange” sea (u, u, d, d) quarks u s “strange” sea (s, s) quarks s Momentum: Spin: Mass: Charge and current: There has been a decade long effort to measure the vector strange form factors.

25. Strange Vector Form Factors – GEs and GMs The strange vector form factors measure the contribution of the strange quark sea to the electromagnetic properties of the nucleon. Strange electric form factor: measures the contribution of the strange quark sea to the nucleon’s spatial charge distribution. Strange magnetic form factor: measures the contribution of the strange quark sea to the nucleon’s spatial magnetization distribution.

26. Parity Violating Electron Scattering - Probe of Neutral Weak Form Factors polarized electrons, unpolarized target Strange electric and magnetic form factors, + axial form factor At a given Q2 decomposition of GsE, GsM, GeA Requires 3 measurements: Forward angle e + p (elastic) Backward angle e + p (elastic) Backward angle e + d (quasi-elastic)

27. Results of Strange Form Factor Measurements - 2005 • Measurements at Q2 = 0.1 GeV2 • MIT-Bates (SAMPLE) • JLAB (HAPPEx) • Mainz (A4) from G0 and Happex at JLAB

28. Strange Form Factor Measurements - speculation The current strange form factor data indicates non-zero values at the ~ 2 σ level. If the true values are anywhere near the central values, these are not small effects; ie. experiment has not yet ruled out potentially large strange quark sea contributions to the nucleon’s electromagnetic properties. Results of global fits to all data (need to multiply by -1/3 to get contribution) from D. Beck More data coming in 2005-2006 from JLAB and Mainz

29. The Qweak Apparatus (Calibration Mode Only - Production & Calibration Modes) Quartz Cherenkov 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

30. QpWeak Toroidal Magnet - QTOR • 8 toroidal coils, 4.5m long along beam • Resistive, similar to BLAST magnet • Pb shielding between coils • Coil holders & frame all Al • Bdl ~ 0.7 T-m • bends elastic electrons ~ 10o • current ~ 9500 A • Status:  coils being wound in France •  support stand designed, out • for bid

31. Inelastic/Elastic Separation in QpWeak View Along Beamline of QpWeak Apparatus - Simulated Events rectangular quartz bar; 18 cm wide X 2 meters long Central scattering angle: ~8° ± 2 Phi Acceptance: > 50% of 2 Average Q²: 0.030 GeV2 Acceptance averaged asymmetry: –0.29 ppm Integrated Rate (per detector): ~801 MHz Inelastic/Elastic ratio: ~0.026% Very clean elastic separation!

32. The QpWeak Detector and Electronics System • Focal plane detector requirements: • Insensitivity to background , n, . • Radiation hardness (expect > 300 kRad). • Operation at counting statistics. • 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 5 inch S20 • photocathode PMTs (expect ~ 100 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.

33. The QpWeak Liquid Hydrogen Target • Target Concept: • Similar in design to SAMPLE and G0 targets •  longitudinal liquid flow •  high stream velocity achieved with perforated, tapered “windsock” • QpWeak Target parameters/requirements: • Length = 35 cm • Beam current = 180 A • Power = 2200 W beam + 300 W heater • Raster size ~4 mm x ~4 mm square • Flow velocity > 700 cm/s • Density fluctuations (at 15 Hz) < 5x10-5

34. Limiting the Target “boiling noise” Contribution • Construct target that does not “boil" at a level << 50ppm/pulse pair level (assuming a 30Hz helicity reversal). Options: large raster size, faster pump speed, better cooled windows.... • Use Luminosity monitors to normalize experiment instead of beam current. • Assume “boiling” is not a resonant phenomena and “noise” is the result of small “bubbles” formed along the target length being ejected from the beam region. Decrease relative contribution of “boiling” by increasing the reversal/data readout rate. noise/pulse pair decreases as the reversal/readout frequency is raised. • Target starts to appear as “solid” w.r.t. any single asymmetry calculation.

35. photocathode anode Laser -100 kV - e Cs NF 3 Polarized Electron Guns at JLab HV insulator The polarized electrons are generated by photoemission from a GaAs semiconductor with polarized laser light NEG pumps NEG-coated Beamline Strained GaAs in Gun2 (“old” material) ~ 75% Polarized Strained-superlattice GaAs In Gun3 (“new” material) ~ 85% Polarized

36. Example: Typical goals for run-averaged beam properties Position: Intensity: keep small with feedback and careful setup keep small with symmetrical detector setup Helicity Correlated Beam Properties: False Asymmetry Corrections DP = P+ – P- Y = Detector yield (P = beam parameter ~energy, position, angle, intensity)

37. The QpWeak Luminosity Monitor • Luminosity monitor Symmetric array of 8 quartz Cerenkov detectors instrumented with rad hard PMTs operated in “vacuum photodiode mode” & integrating readout at small  (~ 0.8). 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.

38. Q2Determination Quartz Cherenkov Bars (insensitive to non-relativistic particles) Region 1: GEM Gas Electron Multiplier Region 2: Horizontal drift chamber location e- beam Expected Q2 distribution Region 3:Vertical Drift chambers Trigger Scintillator Use low beam current (~ few nA) to run in “pulse counting” mode with a tracking system to determine the “light-weighted” Q2 distribution. Region 1 + 2 chambers --> determine value of Q2 Region 3 chamber --> efficiency map of quartz detectors

39. Precision Polarimetry Hall C has existing ~1% precision Moller polarimeter • Present limitations: • IMax ~ 10 A. • At higher currents the Fe target depolarizes. • Measurement is destructive • Plan to upgrading Møller: • Measure Pbeam at 100 A or higher, quasi-continuously • Trick: kicker + strip or wire target (early tests look promising – tested up to 40 A so far) • Schematic of planned new Hall C Compton polarimeter.

40. Summary • Completed low energy Standard Model tests are consistent with Standard • Model “running of sin2W” • SLAC E158 (running verified at ~ 6 level) - leptonic • Cs APV (running verified at ~ 4 level) – semi-leptonic, “d-quark dominated” • Upcoming QpW Experiment • Precision measurement of the proton’s weak charge in the simplest system. • Sensitive search for new physics with CL of 95% at the~ 2.3 TeV scale. • Fundamental10 measurement of the running of sin2W at low energy. • Currently in process of 3 year construction cycle; goal is to have multiple runs in 2008 – 2009 timeframe • Possible 12 GeV Parity-Violating Moller Experiment at JLAB • Conceptual design indicates reduction of E158 error by ~5 may be possible at 12 GeV JLAB. • weak charge triad  • (Ramsey-Musolf)