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Understanding Strangeness in Nucleons: Contributions of Strange Quarks

This presentation by Jacques Arvieux at the Hadron Structure conference details our current knowledge of strangeness in nucleons, especially focusing on the role of strange quarks. It explores various methods to measure nucleon form factors in elastic and parity-violating electron scattering, with special emphasis on the axial form factor and experimental results. The goal is to determine the contributions of strange quarks to the nucleon's electromagnetic properties, thereby enhancing our understanding of non-perturbative QCD and nucleon structure.

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Understanding Strangeness in Nucleons: Contributions of Strange Quarks

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

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

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

  4. NUCLEON FORM-FACTORS IN ELASTIC SCATTERING (vector term) neutral weak form factors • Nucleon form factors • 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% Weak amplitude = 10-5 x Electromagnetic Amplitude

  5. 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)

  6. 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

  7. ASYMMETRY INCLUDING ELECTROWEAK CORRECTIONS with and

  8. 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. BUTWHAT 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, includingDs (next talk)

  9. 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

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

  11. 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

  12. REVIEW OF EXISTING EXPERIMENTAL RESULTS • 1) SAMPLE (MIT-Bates): 3 experiments • 1 exp on hydrogen in 1998 atQ2 = 0.1 (GeV/c)2 • 1 exp on deuterium in 1999 atQ2 = 0.1 (GeV/c)2 • 1 exp in 2001 atQ2 = 0.03 (GeV/c) • 2) HAPPEX (Jefferson-Lab): 4experiments • 1 exp in 1998 atQ2 = 0.45 (GeV/c)2 • 2 experiments on He and H atQ2 = 0.1 (GeV/c)2 • 3) PV-A4 (MAMI-Mainz): 2 experiments • 1 exp at on HQ2 = 0.23 (GeV/c)2published in Jan 2004 • 1 exp on H atQ2 = 0.1 (GeV/c)2published 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

  13. 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

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

  15. HAPPEX I RESULTS

  16. 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)

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

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

  19. 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 Gdipolefor Q2 = 0.12-1.0 (GeV/c)2 • Forward and backwardangle parity-violating e-p elasticand 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

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

  21. Parity Quality Beam Total of 744 hours (103 Coulombs)of parity quality beam with a 4 cut on parity quality. All parity quality specs have been achieved!!

  22. F&W Arr HAPPEX G0 DATA: GEs + h GMs • 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

  23. s GE s GM World Data @ Q2 = 0.1 GeV2 = -0.013  0.028 = +0.62  0.31  0.62 2s • 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 http://www.npl.uiuc.edu/exp/G0/Forward

  24. 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

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

  26. 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 / GMSseparation • Final precision hampered by uncertainties in some parameters: • - neutron electric form factor • - Ds • - Axial form factor (next talk…….)

  27. END

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