Contributions of Strange Quarks to Proton Structure

1. Contributions of Strange Quarks to Proton Structure Doug Beck UIUC 26 Oct. 2005 • Outline: • Physics motivation • Experiments • Results • Speculation

2. Physics Motivation

3. Strange Quark Observables 0.01 0 -0.01 -0.02 -0.03 -0.04 0 0.1 0.2 0.3 0.4 0.5 x x[s(x)-s(x)] • scalar matrix element • . • see talk by M. Sainio, Th. 2:45 • momentum carried by strange quarks • . NuTEV hep-ex/9906037 • . • spin carried by strange quarks • as determined in sum rule • Ds ~ -0.1 - 0 • as determined in semi-inclusive Ds(x) • see talk by Hal Jackson (Tues. 2:30) • vector matrix elements (Mon. 2:30) CTEQ6M, NLO NuTEV hep-ex/0405037

4. Vector Quark Currents in the Nucleon • Measure • e.g. • note then charge symmetry(see G. A. Miller PRC 57 (98) 1492.) dropping the p superscripts on the left

5. . , Non-Zero? GE GM s s s rs rs s s ms ms s • charge distribution • if s, s are separated, non-zero net contribution • convection current • if s, s are separated, non-zero net contribution • spin current • spin triplet: moments cancel • spin singlet: zero net moment, zero net convection • also requires separation

6. Parity-Violating Electron Scattering g e p Z e p • contributes to electron scattering - interference term: large x small • Interference term violates parity: usewhere

7. Experiments

8. Summary of PV Electron Scattering Experiments publishing,running publishing,running 2006 published x2, running published, running 2008 K. Kumar

9. SAMPLE Experiment Caltech, Illinois, Kentucky, LaTech, Maryland, MIT, Virginia Tech, W&M • Measure GM (Q2 = 0.1 GeV2) for 1H,2H Z Ebeam = 200 MeV Ibeam = 40 mA Pbeam = 35% Dq = 130 - 170o DW = 1.5 sr ltarget = 40 cm L = 4.3 x 1038 cm-2 s-1 A ~ -7 ppm

10. HAPPEx (JLab Hall A) Pb-Sci Calorimeters HRS Spectrometers Electron Beam LH2 Target 10 5 Asymmetry (ppm) 0 -5 -10 Data Set Number 0 1 2 3 4 5 6 • Measured GEs + 0.39 GMs at Q2 = 0.48 GeV2 • 2004 runs: 1H, 4He at 0.11 GeV2 Ebeam = 3.2 GeV Ibeam ~ 50 mA Pbeam = 80% q = 60 DW = (3.7 msr) x 2 ltarget = 20 cm L = ~2 x 1038 cm-2 s-1 A ~ -2, +8 ppm HAPPEx nucl-ex/0506010

11. PVA4 (Mainz) Counts Channel • Measure GEs + 0.11 GMs at Q2 = 0.1 GeV2 • have also measured at Q2 = 0.23 GeV2 Second measurement Ebeam = 0.57 GeV Ibeam = 20 mA Pbeam = 80% q = 350 DW = 0.7 sr ltarget = 10 cm L = 0.5 x 1038 cm-2 s-1 A ~ -2 ppm • Q2=0.1 GeV2 • Ameas = -1.36 ± 0.29± 0.13 ppm • Ath = -2.06 ± 0.14 ppm • PRL 94 (05) 152001

12. G0 Experiment (JLab Hall C) GM GE Z Z • Measure , • different linear combination of u, d and s contributions than e.m. form factors • strange quark contributions to sea • Measure forward and backward asymmetries • recoil protons for forward measurement • electrons for backward measurements • elastic/inelastic for 1H, elastic for 2H • Forward measurements complete (101 Coulombs) Ebeam = 3.03 GeV, 0.36 - 0.69 GeV Ibeam = 40 mA, 80 mA Pbeam = 75%, 80% q = 52 – 760, 104 - 1160 DW = 0.9 sr, 0.5 sr ltarget = 20 cm L = 2.1, 4.2 x 1038 cm-2 s-1 A ~ -1 to -50 ppm, -12 to -70 ppm

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

14. Results

15. G0 Experimental Asymmetries GE GM s s • “no vector strange” asymmetry, ANVS, is A( , = 0) • em form factors: Kelly PRC 70 (2004) 068202 • inside error bars: stat, outside: stat. & pt-pt syst. http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001

16. Strange Quark Contribution • Strange quark contribution to asymmetry http://www.npl.uiuc.edu/exp/G0/Forward

17. Strange Quark Contribution to Proton http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001

18. . , Data @ Q2 = 0.1 GeV2 GE GM s s s GE s GM = -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 http://www.npl.uiuc.edu/exp/G0/Forward

19. . , Data @ Q2 = 0.1 GeV2 GE GM s s s GE p s n GM GM GM = -0.013  0.028 = +0.62  0.31 (0.1 GeV2) = 2.12: u: 2.28  0.21 d: 0.03  0.11 s: -0.21  0.11 (0.1 GeV2) = -1.42: u: -0.07  0.11 d: -1.14  0.21 s: -0.21  0.11

20. Speculation

21. Simple Fits to All Hydrogen Data GE GM s s • Fit with simple forms for , à la Kelly with from Q2 = 0.1 GeV2 result, dipole ff

22. “Fit” to All Hydrogen Data c1 = -0.08 c2 = -0.5 d1 = -5.7  1.0 d2 = 19  3 d3 = 1 LM,S = L2 /1.3 2

23. “Fit” to All Hydrogen Data c1 = -0.08 c2 = -0.5 d1 = -5.7  1.0 d2 = 19  3 d3 = 1 LM,S = L2 /1.3 2 Remember the factor of -1/3

24. Future Running: Separation of , . GE GM s s • HAPPEx (forward angle) • reduce uncertainties for H and He by x2-3 at Q2 = 0.1 GeV2 • H at Q2 = 0.63 GeV2, uncertainties x3 smaller than original • PVA4 (backward angle) • start with H at Q2 = 0.23 GeV2: is GE < 0?? • can run H & D for Q2 < 1 GeV2 • G0 (backward angle) • start with H, D at Q2 = 0.63 GeV2: cancellation of GE and GM at high Q2?? • scheduled • summer ’06: H (D) at Q2 = 0.23 GeV2: is GE < 0?? • conditionally approved s ~ s s

25. Summary • Parity-violating elastic electron scattering measures strange quark vector currents • Four new forward angle results in 2005 • PVA4: H @ Q2 = 0.1 GeV2 • HAPPEx: H @ Q2 = 0.1 GeV2 • HAPPEx: He @ Q2 = 0.1 GeV2 • G0 H @ Q2 = 0.1 – 1 GeV2 • Results self-consistent • Emerging picture • GM > 0 at low Q2 - likely • some cancellation of GE and GM likely • hint that GE < 0 at medium Q2 s s s s