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Parity-Violating Electron Scattering on Hydrogen and Helium …

Parity-Violating Electron Scattering on Hydrogen and Helium …. P. A. Souder Syracuse University. and Strangeness in the Nucleon. Representing the HAPPEx II Collaboration. Summary of a more detailed seminar at JLab by K. Paschke. 60 Ni. 60 Co. Weak decay of 60 Co Nucleus.

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Parity-Violating Electron Scattering on Hydrogen and Helium …

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  1. Parity-Violating Electron Scattering on Hydrogen and Helium … P. A.Souder Syracuse University and Strangeness in the Nucleon Representing the HAPPEx II Collaboration Summary of a more detailed seminar at JLab by K. Paschke PV in Electron Scattering on H and He P. A. Souder

  2. 60Ni 60Co Weak decay of 60Co Nucleus 50 Years of Charged Weak Interactions Issues in weak interactions the search for new physics: Physics beyond V-A? Effect of mν? CKM Unitarity? Time reversal Symmetry? Other “Nuclei” 21Na μ n Weak interactions also provide a novel probe of QCD PV in Electron Scattering on H and He P. A. Souder

  3. Neutral Currents andWeak-Electromagnetic Interference Electron Scattering off Nucleons & Nuclei PV in Electron Scattering on H and He P. A. Souder

  4. Nucleon charge and magnetization distributions: GE for the neutron GE(Q2), GM(Q2) GEp(0) = 1 GMp(0) = +2.79  p charge distribution: +ρ core, -ρ fringe, charge radius electric and magnetic form factors GEn(0) = 0 GMn(0) = -1.91  n GEn r2 rs(r) r [fm] Q2 (GeV/c)2 Elastic Scattering and Form Factors Neglecting recoil and spin: Obtain Fourier transform of charge distribution PV in Electron Scattering on H and He P. A. Souder

  5. Breaking of SU(3) flavor symmetry introduces uncertainties ? The Question: What is the Role ofStrangeness in the Nucleon? One example: Possible explanation that would influence Form Factors: PV in Electron Scattering on H and He P. A. Souder

  6. Can We Measure the Contribution of Strange Quarks to From Factors? Yes! PV in Electron Scattering on H and He P. A. Souder

  7. Detailed Formulae: Clean Probe of StrangenessInside the Nucleon Hydrogen • Measurement of APV yields linear combination of GsE, GsM 4He • Sensitive only to GsE PV in Electron Scattering on H and He P. A. Souder

  8. Extrapolated from G0 Q2=[0.12,0.16] GeV2 Dc2 = 1 95% c.l. World Data (Sept. 05) at Q2 ~ 0.1 GeV2 Note: excellent agreement of world data set GEs = -0.12 ± 0.29 GMs = 0.62 ± 0.32 Would imply that 5-10% of nucleon magnetic moment is Strange Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account PV in Electron Scattering on H and He P. A. Souder

  9. Extrapolated from G0 Q2=[0.12,0.16] GeV2 Dc2 = 1 95% c.l. Theory Calculations 16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992). 17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996). 18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999). 19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001). 20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002). 21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003). 22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025 19 21 22 16 17 18 PV in Electron Scattering on H and He P. A. Souder

  10. Example at JLab: HAPPEX Experiment 1998-99: Q2=0.5 GeV2, 1H 2004-06: Q2=0.1 GeV2, 1H, 4He 2008:Q2=0.6, 1H The HAPPEX Collaboration California State University, Los Angeles - Syracuse University - DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator Facility- INFN, Rome - INFN, Bari - Massachusetts Institute of Technology - Harvard University – Temple University – Smith College - University of Virginia - University of Massachusetts – College of William and Mary PV in Electron Scattering on H and He P. A. Souder

  11. A B C Hall A Jefferson Laboratory CEBAF Continuous Electron Beam Accelerator Facility • Features: • Polarized Source • Quiet Accelerator • Precision • Spectrometers • in Hall A Polarized e- Source PV in Electron Scattering on H and He P. A. Souder

  12. Hall A Polarimeters Compton 1.5-3% syst Continuous Møller 2-3% syst Target 400 W transverse flow 20 cm, LH2 20 cm, 200 psi 4He High Resolution Spectrometer S+QQDQ 5 mstr over 4o-8o PV in Electron Scattering on H and He P. A. Souder

  13. PMT Elastic Rate: 1H: 120 MHz Cherenkov cones 4He: 12 MHz PMT Overlap the elastic line above the focal plane and integrate the flux Very clean separation of elastic events by HRS optics  High Resolution Spectrometers 100 x 600 mm 12 m dispersion sweeps away inelastic events Large dispersion and heavy shielding reduce backgrounds at the focal plane PV in Electron Scattering on H and He P. A. Souder

  14. Acceptance Rolloff Background-4He Dedicated runs at very low current using track reconstruction of the HRS Dipole field scan to measure the probability of rescattering inside the spectrometer Helium Helium QE in detector: 0.15 +/- 0.15% Helium QE rescatter: 0.25 +/- 0.15% Al fraction: 1.8 +/- 0.2% Hydrogen: Al fraction 0.75 +/- 25 % Hydrogen Tail + Delta rescatter: <0.1% Total systematic uncertainty contribution ~40 ppb (Helium), ~15ppb (Hydrogen) PV in Electron Scattering on H and He P. A. Souder

  15. - N N = R L A LR + N N R L Polarized Electrons for Measuring Asymmetries >85% Polarization Rapid Helicity Flip: Measure the asymmetry at few 10-4 level, 30 million times Slow Helicity Flip: check answer . PV in Electron Scattering on H and He P. A. Souder

  16. Rapid Helicity Flip: Measure the asymmetry at few 10-4 level, 30 million times • Analog integration of rates ~100 MHz • High luminosity: thick targets, high beam current • Control noise (target, electronics) • Polarized source uses optical pumping of strained photocathode: high polarization and rapid flip Measurement of P-V Asymmetries 5% Statistical Precision on 1 ppm -> requires 4x1014 counts Statistics: high rate, low noise Systematics: beam asymmetries, backgrounds, Helicity correlated DAQ Normalization: Polarization, Linearity, Background PV in Electron Scattering on H and He P. A. Souder

  17. Helicity signal to driver removed Problem: Helicity signal deflecting the beam through electronics “pickup” Large beam deflections even when Pockels cell is off Beam Position Differences, Helium 2005 • All’s well that ends well • Problem clearly identified as beam steering from electronic cross-talk • Tests verify no helicity-correlated electronics noise in Hall DAQ at sub ppb level • Large position differences mostly cancel in average over both detectors X Angle BPM micron Raw ALL Asymetry ppm Helicity signal to driver reversed PV in Electron Scattering on H and He P. A. Souder

  18. Corrected Left Asymmetry Raw Left Asymmetry Corrected Right Asymmetry Raw Right Asymmetry Beam Position Differences, Helium 2005 Beam Asymmetries Energy: -3ppb X Target: -5 nm X Angle: -28 nm Y Target :-21 nm Y Angle: 1 nm ppm ppm ppm Total Corrections: Left: -370 ppb Right: 80 ppb All: 120 ppb ppm PV in Electron Scattering on H and He P. A. Souder

  19. X Angle BPM Beam Position Differences, Hydrogen 2005 Surpassed Beam Asymmetry Goals for Hydrogen Run Energy: -0.25 ppb X Target: 1 nm X Angle: 2 nm Y Target : 1 nm Y Angle: <1 nm micron Spectacular performance of source and accelerator (We should have published on-line Results.) Corrected and Raw, Left arm alone, Superimposed! ppm Total correction for beam position asymmetry on Left, Right, or ALL detector: 10 ppb PV in Electron Scattering on H and He P. A. Souder

  20. Summary of Data Runs: HAPPEX-II PV in Electron Scattering on H and He P. A. Souder

  21. Asymmetry (ppm) Slug 1H Preliminary Results Raw Parity Violating Asymmetry ~25 M pairs, width ~540 ppm Araw correction ~11 ppb Helicity Window Pair Asymmetry Q2 = 0.1089 ± 0.0011GeV2 Araw = -1.418 ppm 0.105 ppm (stat) PV in Electron Scattering on H and He P. A. Souder

  22. Asymmetry (ppm) Slug 4He Preliminary Results Raw Parity Violating Asymmetry 35 M pairs, total width ~1130 ppm Araw correction ~ 0.12 ppm Helicity Window Pair Asymmetry Q2 = 0.07725 ± 0.0007 GeV2 Araw = 5.253 ppm 0.191 ppm (stat) PV in Electron Scattering on H and He P. A. Souder

  23. COMPTON POLARIMETRY Hall A e- detector Compton Int. Point g detector • Non-invasive, continuous polarimetry • 2% systematic error at 3 GeV for HAPPEX-II • Independent photon and electron analyses • Cross-checked with Hall A Moller, 5 MeV Mott PV in Electron Scattering on H and He P. A. Souder

  24. Hydrogen: 86.7% ± 2% Helium: 84.0% ± 2.5% Compton Polarimetry Electron Detector analysis Cross-checked with Møller Helium ran with lower beam energy, making the analysis significantly more challenging. New developments in both photon and electron analyses in preparation: anticipate <2% systematic uncertainty PV in Electron Scattering on H and He P. A. Souder

  25. Q2 measured using standard HRS tracking package, with reduced beam current Goal: Measuring Q2 • Central scattering angle must be measured to dq< 0.25% • Asymmetry distribution must be averaged over finite acceptance Nuclear recoil, using water cell optics target:dp between elastic and excited state peaks reduces systematic error from spectrometer calibration. At Q2~0.1 GeV2 (6o) in 2004: Achieved dq~ 0.3% PV in Electron Scattering on H and He P. A. Souder

  26. Error Budget 2005 Helium Hydrogen PV in Electron Scattering on H and He P. A. Souder

  27. HAPPEX-II 2005 Preliminary Results HAPPEX-4He: Q2 = 0.0772 ± 0.0007 (GeV/c)2 APV = +6.43  0.23 (stat)  0.22 (syst) ppm A(Gs=0) = +6.37 ppm GsE = 0.004  0.014(stat)  0.013(syst) HAPPEX-H: Q2 = 0.1089 ± 0.0011 (GeV/c)2 APV = -1.60  0.12 (stat)  0.05 (syst) ppm A(Gs=0) = -1.640 ppm 0.041 ppm GsE + 0.088 GsM = 0.004  0.011(stat)  0.005(syst)  0.004(FF) PV in Electron Scattering on H and He P. A. Souder

  28. HAPPEX-II 2005 Preliminary Results • Three bands: • Inner: Project to axis for 1-D error bar • Middle: 68% probability contour • Outer: 95% probability contour Preliminary Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account PV in Electron Scattering on H and He P. A. Souder

  29. World Data near Q2 ~0.1 GeV2 GMs = 0.28 +/- 0.20 GEs = -0.006 +/- 0.016 ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of Electric distribution HAPPEX only fit suggests something even smaller: GMs = 0.12 +/- 0.24 GEs = -0.002 +/- 0.017 Preliminary Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account PV in Electron Scattering on H and He P. A. Souder

  30. World data confronts theoretical predictions 16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992). 17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996). 18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999). 19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001). 20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002). 21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003). 22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025 Preliminary PV in Electron Scattering on H and He P. A. Souder

  31. A Simple Fit (for a simple point) Simple fit: GEs = r_s*t GMs = mu_s Includes only data Q2 < 0.3 GeV2 Includes SAMPLE constrainted with GA theory and HAPPEX-He 2004, 2005 G0 Global error allowed to float with unit constraint Nothing intelligent done with form factors, correlated errors, etc. • For an example of a fit that could be taken seriously: • R. Young, Roche, Carlini and Thomas, nucl-ex/0604010 • Suggests that the question of the axial form factor corrections is still very much alive. Will back angle measurements give us more information on strange form factors, or will they instead use the existing constraints on strange form factors to get to the axial term? Preliminary • Quantitative values should NOT be taken very seriously, but some clear, basic points: • The world data is consistent. • Rapid Q2 dependence of strange form-factors is not required. • Measurable contributions at higher Q2 are not definitively ruled out. (To be tested by HAPPEX-III, G0 and A4 backangle.) PV in Electron Scattering on H and He P. A. Souder

  32. G0 backward HAPPEX-III GEs 0.6 GeV2 GMs Summary and Outlook Preliminary • Suggested large values at Q2~0.1 GeV2 • Ruled out • Large possible cancellation at Q2~0.2 GeV2 • Very unlikely given constraint at 0.1 GeV2 • G0 back angle at low Q2 (error bar~1.5% of mp) maintains sensitivity to discover GMS • Possible large values at Q2>0.4 GeV2 • G0 backangle, Running now! • HAPPEX-III - 2008 PV in Electron Scattering on H and He P. A. Souder

  33. PV in Electron Scattering on H and He P. A. Souder

  34. EM Form Factors Electromagnetic form factors parameterized as by: Friedrich and Walcher, Eur. Phys. J. A, 17, 607 (2003) GEn from BLAST: Uncertainty at 7-8% PV in Electron Scattering on H and He P. A. Souder

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