April 23, 2006PV in Electron Scattering on H and He P. A. Souder Parity-Violating Electron Scattering on Hydrogen and Helium and Strangeness in the Nucleon P. A. Souder Syracuse University Representing the HAPPEx II Collaboration Summary of a more detailed seminar at JLab by K. Paschke April 23, 2006PV in Electron Scattering on H and He P. A. Souder Weak decay of 60 Co Nucleus 60 Co 60 Ni 50 Years of Charged Weak Interactions Issues in weak interactions the search for new physics: Other Nuclei 21 Na n Physics beyond V-A? Effect of m ? CKM Unitarity? Time reversal Symmetry? Weak interactions also provide a novel probe of QCD April 23, 2006PV in Electron Scattering on H and He P. A. Souder Electron Scattering off Nucleons & Nuclei Neutral Currents and Weak-Electromagnetic Interference April 23, 2006PV in Electron Scattering on H and He P. A. Souder Q 2 (GeV/c) 2 GEnGEn r 2 s (r) r [fm] G E for the neutron charge distribution: + core, - fringe, charge radius Neglecting recoil and spin: Obtain Fourier transform of charge distribution Nucleon charge and magnetization distributions: G E (Q 2 ), G M (Q 2 ) G E p (0) = 1 G M p (0) = p electric and magnetic form factors G E n (0) = 0 G M n (0) = n Elastic Scattering and Form Factors April 23, 2006PV in Electron Scattering on H and He P. A. Souder The Question: What is the Role of Strangeness in the Nucleon? ? Breaking of SU(3) flavor symmetry introduces uncertainties Possible explanation that would influence Form Factors: One example: April 23, 2006PV in Electron Scattering on H and He P. A. Souder Can We Measure the Contribution of Strange Quarks to From Factors? Yes ! April 23, 2006PV in Electron Scattering on H and He P. A. Souder Detailed Formulae: Clean Probe of Strangeness Inside the Nucleon Measurement of A PV yields linear combination of G s E, G s M Sensitive only to G s E Hydrogen 4 He April 23, 2006PV in Electron Scattering on H and He P. A. Souder Extrapolated from G0 Q 2 =[0.12,0.16] GeV 2 95% c.l. 2 = 1 World Data (Sept. 05) at Q 2 ~ 0.1 GeV 2 G E s = 0.29 G M s = 0.62 0.32 Would imply that 5-10% of nucleon magnetic moment is Strange Note: excellent agreement of world data set Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account April 23, 2006PV in Electron Scattering on H and He P. A. Souder Extrapolated from G0 Q 2 =[0.12,0.16] GeV 2 95% c.l. 2 = 1 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, (1999). 19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, (2001). 20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, (2002). 21. Lattice - R. Lewis et al., Phys. Rev. D 67, (2003). 22. Lattice + charge symmetry - Leinweber et al, Phys. Rev. Lett. 94, (2005) & hep-lat/ April 23, 2006PV in Electron Scattering on H and He P. A. Souder Summary (Sept 2005) GEsGEs 0.6 GeV 2 G0 backward HAPPEX-III GMsGMs Suggested large values at Q 2 ~0.1 GeV 2 HAPPEX-II, H and He running now! Possible large values at Q 2 >0.4 GeV 2 G 0 backangle, approved for Spring 06 HAPPEX-III, conditionally approved ? A4 backangle? Large possible cancellation at Q 2 ~0.2 GeV 2 G 0 backangle, conditionally approved for Summer 06 A4 backangle? April 23, 2006PV in Electron Scattering on H and He P. A. Souder 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 : Q 2 =0.5 GeV 2, 1 H : Q 2 =0.1 GeV 2, 1 H, 4 He 2008:Q 2 =0.6, 1 H Example at JLab: HAPPEX Experiment April 23, 2006PV in Electron Scattering on H and He P. A. Souder Jefferson Laboratory Polarized e - Source Hall A Continuous Electron Beam Accelerator Facility CEBAF Features: 1.Polarized Source 2.Quiet Accelerator 3.Precision Spectrometers in Hall A April 23, 2006PV in Electron Scattering on H and He P. A. Souder Target 400 W transverse flow 20 cm, LH2 20 cm, 200 psi 4 He High Resolution Spectrometer S+QQDQ 5 mstr over 4 o -8 o Hall A Compton 1.5-3% syst Continuous Mller 2-3% syst Polarimeters April 23, 2006PV in Electron Scattering on H and He P. A. Souder Cherenkov cones PMT Elastic Rate: 1 H: 120 MHz 4 He: 12 MHz High Resolution Spectrometers 100 x 600 mm 12 m dispersion sweeps away inelastic events Very clean separation of elastic events by HRS optics Overlap the elastic line above the focal plane and integrate the flux Large dispersion and heavy shielding reduce backgrounds at the focal plane April 23, 2006PV in Electron Scattering on H and He P. A. Souder Background- 4 He Dedicated runs at very low current using track reconstruction of the HRS Dipole field scan to measure the probability of rescattering inside the spectrometer Acceptance Rolloff Helium Helium QE in detector: /- 0.15% Helium QE rescatter: /- 0.15% Al fraction: 1.8 +/- 0.2% Hydrogen: Al fraction /- 25 % Hydrogen Tail + Delta rescatter: 85% Polarization April 23, 2006PV in Electron Scattering on H and He P. A. Souder Measurement of P-V Asymmetries Statistics: high rate, low noise Systematics: beam asymmetries, backgrounds, Helicity correlated DAQ Normalization: Polarization, Linearity, Background 5% Statistical Precision on 1 ppm -> requires 4x10 14 counts Rapid Helicity Flip: Measure the asymmetry at few 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 April 23, 2006PV in Electron Scattering on H and He P. A. Souder Beam Position Differences, Helium 2005 Problem: Helicity signal deflecting the beam through electronics pickup Large beam deflections even when Pockels cell is off Helicity signal to driver reversed Helicity signal to driver removed Alls 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 Raw ALL Asymetry micron ppm April 23, 2006PV in Electron Scattering on H and He P. A. Souder Beam Position Differences, Helium 2005 Raw Left Asymmetry Raw Right Asymmetry Corrected Right Asymmetry Corrected Left Asymmetry Beam Asymmetries Energy: -3ppb X Target: -5 nm X Angle: -28 nm Y Target :-21 nm Y Angle: 1 nm Total Corrections: Left: -370 ppb Right: 80 ppb All: 120 ppb ppm April 23, 2006PV in Electron Scattering on H and He P. A. Souder Beam Position Differences, Hydrogen 2005 X Angle BPM Energy: ppb X Target: 1 nm X Angle: 2 nm Y Target : 1 nm Y Angle: A stat ~ 0.74 ppm June July 2004 HAPPEX-H about 9M pairs at 620 ppm => A stat ~ 0.2 ppm July-Sept 2005 HAPPEX-He about 35M pairs at 1130 ppm => A stat ~ 0.19 ppm Oct Nov 2005 HAPPEX-H about 25M pairs at 540 ppm => A stat ~ ppm Summary of Data Runs: HAPPEX-II April 23, 2006PV in Electron Scattering on H and He P. A. Souder 1 H Preliminary Results Q 2 = GeV 2 A raw = ppm ppm (stat) A raw correction ~11 ppb Raw Parity Violating Asymmetry Helicity Window Pair Asymmetry ~25 M pairs, width ~540 ppm Asymmetry (ppm) Slug April 23, 2006PV in Electron Scattering on H and He P. A. Souder 4 He Preliminary Results Q 2 = GeV 2 A raw = ppm ppm (stat) Raw Parity Violating Asymmetry Helicity Window Pair Asymmetry 35 M pairs, total width ~1130 ppm A raw correction ~ 0.12 ppm Slug Asymmetry (ppm) April 23, 2006PV in Electron Scattering on H and He P. A. Souder COMPTON POLARIMETRY Compton Int. Point detector e - detector Hall A 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 April 23, 2006PV in Electron Scattering on H and He P. A. Souder Compton Polarimetry Hydrogen: 86.7% 2%Helium: 84.0% 2.5% Electron Detector analysis Cross-checked with Mller Helium ran with lower beam energy, making the analysis significantly more challenging. New developments in both photon and electron analyses in preparation: anticipate 0.4 GeV 2 G 0 backangle, Running now! HAPPEX-III Large possible cancellation at Q 2 ~0.2 GeV 2 Very unlikely given constraint at 0.1 GeV 2 G0 back angle at low Q 2 (error bar~1.5% of p ) maintains sensitivity to discover G M S Preliminary 0.6 GeV 2 G0 backward HAPPEX-III GMsGMs GEsGEs April 23, 2006PV in Electron Scattering on H and He P. A. Souder April 23, 2006PV in Electron Scattering on H and He P. A. Souder EM Form Factors Electromagnetic form factors parameterized as by: Friedrich and Walcher, Eur. Phys. J. A, 17, 607 (2003) FFError GEpGEp 2.5% GMpGMp 1.5% GEnGEn 10% GMnGMn 1.5% G A (3) - G A (8) - GEn from BLAST: Uncertainty at 7-8%