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Contributions of Strange Quarks to Proton Structure. Doug Beck UIUC 26 Oct. 2005. Outline: Physics motivation Experiments Results Speculation. Physics Motivation. 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)].
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Contributions of Strange Quarks to Proton Structure Doug Beck UIUC 26 Oct. 2005 • Outline: • Physics motivation • Experiments • Results • Speculation
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
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
. , 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
Parity-Violating Electron Scattering g e p Z e p • contributes to electron scattering - interference term: large x small • Interference term violates parity: usewhere
Summary of PV Electron Scattering Experiments publishing,running publishing,running 2006 published x2, running published, running 2008 K. Kumar
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
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
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
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
G0 in Hall C (JLab) superconducting magnet (SMS) cryogenic supply beam monitoring girder scintillation detectors cryogenic target ‘service module’ electron beamline
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
Strange Quark Contribution • Strange quark contribution to asymmetry http://www.npl.uiuc.edu/exp/G0/Forward
Strange Quark Contribution to Proton http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001
. , 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
. , 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
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
“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
“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
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
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