Richard Wilson Harvard University Pert of the HAPPEX Collaboration Summary of more detailed seminars at JLab by K. Paschke and APS by Paul Souder Parity-Violating Electron Scattering on Hydrogen and Helium … And Strangeness in the Nucleon

45 years ago (Spring 1961).... I started my intereest in electron scattering and form factors G e and G m In Breit (brick wall frame) these are the Fourier transforms of charge and magnetic moment distributions Sachs) We defined Ge = F 1 + q 2 /4M 2 κ F 2 and G m = F 1 + κ F 2 because of misuse of F e = F 1 = F Dirac and and F m as F κ J = eG e + eσ x q G m

Q 2 (GeV/c) 2 GEnGEn r 2  s (r) r [fm] G E for the neutron charge distribution: +ρ core, -ρ 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

The DIPOLE FIT The FIT is extraordinarily good. I have never heard a good explanation. It is used for comparison

EM Form Factors Electromagnetic form factors parameterized as by: Friedrich and Walcher, Eur. Phys. J. A, 17, 607 (2003) -G A (8) -G A (3) 1.5%GMnGMn 10%GEnGEn 1.5%GMpGMp 2.5%GEpGEp ErrorFF GEn from BLAST: Uncertainty at 7-8%

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 μ n Physics beyond V-A? Effect of m ν ? CKM Unitarity? Time reversal Symmetry? Weak interactions also provide a novel probe of QCD

Electron Scattering off Nucleons & Nuclei Neutral Currents and Weak-Electromagnetic Interference

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:

Can We Measure the Contribution of Strange Quarks to Form Factors? Yes !

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

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

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/

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 S ummer ’06 A4 backangle?

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 2007:Q 2 =0.6, 1 H Example at JLab: HAPPEX Experiment

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

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 (Saclay) Møller 2-3% syst (JLAB) Polarimeters

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

Harvard Contribution: Also Polarization intensity correlations hence on beam position and asymmetries corrected by feedback (developed in 1986) Integrating electronics (Oliver/Wilson) and avoidance of ground loops

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: <0.1% Total systematic uncertainty contribution ~40 ppb (Helium), ~15ppb (Hydrogen)

Rapid Helicity Flip: Measure the asymmetry at few level, 30 million times LR LR LR NN NN A    Slow Helicity Flip: check answer. Polarized Electrons for Measuring Asymmetries >85% Polarization

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

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 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 Raw ALL Asymetry micron ppm

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

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

June 2004 HAPPEX-He about 3M pairs at 1300 ppm =>  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

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

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)

COMPTON POLARIMETRY (SACLAY) 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

Compton Polarimetry (Saclay) Hydrogen: 86.7% ± 2%Helium: 84.0% ± 2.5% 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

Measuring Q 2 Nuclear recoil, using water cell optics target:  p between elastic and excited state peaks reduces systematic error from spectrometer calibration. At Q 2 ~0.1 GeV 2 (6 o ) in 2004: Achieved  ~ 0.3% Goal: Q 2 measured using standard HRS tracking package, with reduced beam current Central scattering angle must be measured to   < 0.25% Asymmetry distribution must be averaged over finite acceptance

False Asymmetries48 ppb Polarization192 ppb Linearity 58 ppb Radiative Corr. 6 ppb Q 2 Uncertainty58 ppb Al background32 ppb Helium quasi- elastic background 24 ppb Total216 ppb Error Budget 2005 False Asymmetries17 ppb Polarization37 ppb Linearity15 ppb Radiative Corr.3 ppb Q 2 Uncertainty16 ppb Al background15 ppb Rescattering Background 4 ppb Total49 ppb HeliumHydrogen

HAPPEX-II 2005 Preliminary Results A(G s =0) = ppm G s E =  (stat)  (syst) A(G s =0) = ppm  ppm G s E G s M =  (stat)  (syst)  (FF) HAPPEX- 4 He: HAPPEX-H: Q 2 = ± (GeV/c) 2 A PV =  0.12 (stat)  0.05 (syst) ppm Q 2 = ± (GeV/c) 2 A PV =  0.23 (stat)  0.22 (syst) ppm

HAPPEX-II 2005 Preliminary Results Three bands: 1.Inner: Project to axis for 1-D error bar 2.Middle: 68% probability contour 3.Outer: 95% probability contour Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account Preliminary

Previous World Data near Q 2 ~0.1 GeV 2 Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account Preliminary G M s = / G E s = / ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of Electric distribution HAPPEX only fit suggests something even smaller: G M s = / G E s = /

World data confronts theoretical predictions Preliminary 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/

In retirement knocking balls around More fun than a single ball at Hilton Head. (or Acupulco) AND these are polarized! Thank you for your attention