Nucleon Strangeness: What we know and what we are still missing Jacques Arvieux IPN-Orsay Hadron Structure at J-PARC, Tsukuba, 1 December 2005

DIFFERENT TYPES OF POSSIBLE STRANGE CONTRIBUTIONS SCALAR and magnetic moment AXIAL VECTOR (current and magnetization)

WHAT ROLE DO STRANGE QUARKS PLAY? proton u u valence quarks d u gluon “non-strange” sea (u, u ,d, d ) u s “strange” sea (s, s) quarks s Mass: (scalar) Momentum: Spin: (axial) Charge and current: (vector)

NUCLEON FORM-FACTORS IN ELASTIC SCATTERING (vector term) well defined experimental observables provide an important benchmark for testing non-perturbative QCD structure of the nucleon electromagnetic form factors Precision of EM form factors in 0.1 - 1 GeV2 Q2 range ~ 2 - 4% neutral weak form factors Weak amplitude = 10-5 x Electromagnetic Amplitude

PARITY VIOLATING ELECTRON SCATTERING polarized electrons, unpolarized target At tree level: 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) 4. e+ He4 elastic scattering (only GsE)

PARITY VIOLATING ASYMMETRY forward angles HAPPEX, Mainz, G0: sensitive to backward angles SAMPLE, G0: sensitive to and and Overall goal of parity-violating electron scattering programs: axial form factor! Determine and separately over a wide range (0.1 – 1.0) (GeV/c)2 of Q2

ELECTROWEAK CORRECTIONS ASYMMETRY INCLUDING ELECTROWEAK CORRECTIONS with and

CORRECTIONS TO TREE LEVEL CALCULATIONS To determine the strange form factors we must measure the PV asymmetry and compare it to the non-strange asymmetry A0 where strange form factors GES and GMS are set to zero. BUT WHAT IS REALLY A0? To the tree level calculations one should apply the following corrections: 1) One-quark electroweak corrections (Standard Model) 2) Multiquark radiative corrections (Anapole Moment) and make the best choice for the following parameters: 3) Choice of electromagnetic form-factors 5) Axial form-factor, including Ds (next talk)

ELECTROWEAK RADIATIVE CORRECTIONS . 1) One quark corrections: electroweak radiative corrections to e-N scattering . . . 2) Multi-quark corrections: nucleon anapole moment (parity-violating coupling between quarks) . . . . Z,W Anapole moment

PROTON FORM-FACTORS Rosenbluth separation Recoil polarization Comparison of Friedrich- Walcher (blue) and Kelly (green) fits for GEp and GMp Rosenbluth separation Recoil polarization

NEUTRON FORM FACTORS The uncertainties are much larger than for protons and GEn data do not extend to high Q2 data so that this effect is not visible: GEn GMn

REVIEW OF EXISTING EXPERIMENTAL RESULTS 1) SAMPLE (MIT-Bates): 3 experiments 1 exp on hydrogen in 1998 at Q2 = 0.1 (GeV/c)2 1 exp on deuterium in 1999 at Q2 = 0.1 (GeV/c)2 1 exp in 2001 at Q2 = 0.03 (GeV/c) 2) HAPPEX (Jefferson-Lab): 4experiments 1 exp in 1998 at Q2 = 0.45 (GeV/c)2 2 experiments on He and H at Q2 = 0.1 (GeV/c)2 3) PV-A4 (MAMI-Mainz): 2 experiments 1 exp at on H Q2 = 0.23 (GeV/c)2 published in Jan 2004 1 exp on H at Q2 = 0.1 (GeV/c)2 published in Dec 2004 G0 (Jefferson Lab): Q2 = 0.1-1 (GeV/c)2 forward angles on H target in 2004 backward angles on H and D target in 2006

GENERAL EXPERIMENTAL REQUIREMENTS Want to measure APV ~ -3/-40 ppm with precision dAPV /APV ~ 5% Statistics (need 1013 - 1014 events): Reliable high polarization, high current polarized source High power H/D target Large acceptance detector High count rate capability detectors/electronics Systematics (needed to reduce false asymmetries, accurately measure dilution factors): Small helicity-correlated beam properties Capability to isolate elastic scattering from other processes

SUMMARY OF SAMPLE 200 MeV DATA Q2=0.1 (GeV/c)2 D2 H2 Zhu, et al. Using Zhu et al. for GAe(T=1) Combined D2/H2 at 200 MeV

HAPPEX I RESULTS

2004 HAPPEX-II Results HAPPEX-4He: Q2 = 0.091 (GeV/c)2 APV = +6.72  0.84 (stat)  0.21 (syst) ppm A(Gs=0) = +7.507 ppm  0.075 ppm GsE = -0.039  0.041(stat)  0.010(syst)  0.004(FF) Q2 = 0.099 (GeV/c)2 APV = -1.14  0.24 (stat)  0.06 (syst) ppm HAPPEX-H: A(Gs=0) = -1.440 ppm  0.105 ppm GsE + 0.08 GsM = 0.032  0.026(stat)  0.007(syst)  0.011(FF)

RESULTS FROM PV-A4 (MAMI-MAINZ) Note the Negative sign

PRESENT RESULTS BEFORE G0 GES ~ 0 GMS ~ +0.5 mP GEs + a(Q2) GMs GMs GEs Q2 [GeV2]

THE G0 EXPERIMENT AT JLAB Caltech, Carnegie-Mellon, W&M, Hampton, IPN-Orsay, ISN-Grenoble, Kentucky, La.Tech, NMSU, Jlab, TRIUMF, Uconn, UIUC, UMan, UMd, UMass, UNBC, VPI, Yerevan Goal: Determine contributions of strange quarks to charge and magnetization distributions of the nucleon within a few percent of Gdipole for Q2 = 0.12-1.0 (GeV/c)2 Forward and backward angle parity-violating e-p elastic and e-d quasielastic in Jefferson Lab Hall C Kinematics Forward mode: detect recoil protons Backward mode: detect electrons Note that G0= (Gu + Gd + Gs) / 3 is the singlet form-factor

G0 in Hall C at JLAB superconducting magnet (SMS) cryogenic supply beam monitoring girder scintillation detectors cryogenic target ‘service module’ electron beamline

Parity Quality Beam Total of 744 hours (103 Coulombs) of parity quality beam with a 4 cut on parity quality. Beam Parameter Achieved “Specs” Charge asymmetry -0.14 ± 0.32 ppm 1 ppm x position differences 3 ± 4 nm 20 nm y position differences 4 ± 4 nm x angle differences 1 ± 1 nrad 2 nrad y angle differences 1.5 ± 1 nrad Energy differences 29 ± 4 eV 75 eV All parity quality specs have been achieved!!

G0 DATA: GEs + h GMs F&W Arr HAPPEX lines show Friedrich & Walcher, Arrington/Kelly form factors (Kelly = 0) HAPPEX points adjusted to G0 incident energy (DA = 0.03 ppb, 0.13 ppm) DHB 15 May 05

World Data @ Q2 = 0.1 GeV2 GE s GM s = -0.013  0.028 = +0.62  0.31 Contours 1s, 2s 68.3, 95.5% CL Theories Leinweber, et al. PRL 94 (05) 212001 Lyubovitskij, et al. PRC 66 (02) 055204 Lewis, et al. PRD 67 (03) 013003 Silva, et al. PRD 65 (01) 014016 Fix figure http://www.npl.uiuc.edu/exp/G0/Forward

WORLD DATA: Q2 = 0.23 GeV2 Good agreement between G0 and PV-A4 Need backward angle data for separating GEs and GMs DHB 15 May 05

World data: Q2 = 0.477 GeV2 Good agreement between G0 and HAPPEX HAPPEX H G0 Good agreement between G0 and HAPPEX Need backward angle data for separating GES and GMS DHB 15 May 05

CONCLUSIONS Fist measurement of strange form factors at high momentum transfer by G0 Contribution of strange quarks to nucleon form factors is small but definitely non-zero Backward angle data from PVA4 and G0 , combined with new forward HAPPEX point will allow a clean GES / GMS separation Final precision hampered by uncertainties in some parameters: - neutron electric form factor - Ds - Axial form factor (next talk…….)

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