Contributions of Strange Quarks to Proton Structure Doug Beck UIUC - PowerPoint PPT Presentation

Contributions of Strange Quarks to Proton Structure Doug Beck UIUC 24 Apr 06 Outline: 1. Physics motivation 2. Experiments 3. Results 4. Speculation

Strange Quark Observables • scalar matrix element + − – . 2 N s s N N u u d d N ~ 0 . 1 0 . 4 • new review by M. Sainio (PANIC05) 0.01 • momentum carried by strange quarks ( ) 0 + d = ± ± 2 s u 0 . 42 0 . 07 0 . 06 – . x[s(x)-s(x)] -0.01 NuTEV hep-ex/9906037 ( ) ( ) ≅ -0.02 – . s x s x -0.03 • spin carried by strange quarks -0.04 – as determined in sum rule 0 0.1 0.2 0.3 0.4 0.5 x • Δ s ~ -0.1 - 0 CTEQ6M, NLO – as determined in semi-inclusive Δ s(x) NuTEV hep-ex/0405037 • HERMES result (PANIC05) • vector matrix elements

Vector Quark Currents in the Nucleon ∑ γ γ Γ • Measure , p Z , p , n , , : G ~ N e q q N G G G μ i i i i – e.g. ( ) 2 1 γ = − + , p u , p d , p s , p G G G G E , M E , M E , M E , M 3 3 = – note u , p d , n G G charge symmetry = d , p u , n G G (see G. A. Miller PRC 57 (98) 1492.) = s , p s , n G G ( ) γ = − θ − u 2 , p Z , p G 3 4 sin G G then E , M W E , M E , M ( ) γ γ = − θ + − d 2 , p , n Z , p G 2 4 sin G G G E , M W E , M E , M E , M ( ) = − θ γ − γ − s 2 , p , n Z , p G 1 4 sin G G G E , M W E , M E , M E , M dropping the p superscripts on the left

s s . G E , Non-Zero? G M • charge distribution – if s, s are separated, non-zero net s contribution r s • convection current s r s – if s, s are separated, non-zero net contribution μ s μ s • spin current 1 = + s z – spin triplet: moments cancel 2 – spin singlet: zero net moment, zero s s net convection 1 = − s – also requires separation z 2

Parity-Violating Electron Scattering Z , p contributes to electron scattering • G 2 γ γ σ ∝ + Z M M γ Z - interference term: large x small M M e p r ( ) ′ • Interference term violates parity: use e , e Z σ − σ ≡ − PV 5 R L A ~ 10 σ + σ R L e p + + 2 G Q A A A = − F E M A ( ) ( ) πα γ 2 γ 2 ε + τ 4 2 G G E M [ ] ( ) ( ) ( ) − 1 ε θ = + + τ θ where 2 1 2 1 tan / 2 , ( ) γ γ = ε θ = τ Z Z A G G , A G G 2 Q τ = E E E M M M ( ) ( ) , − = ′ 2 − θ ε θ γ 4 M 2 e A 1 4 sin G G p A W M A ) ( ) ( ) ( ′ ε θ = τ + τ − ε 2 1 1

Experiments

Summary of PV Electron Scattering Experiments published (ing) published (ing) 2006 published x2, running published, running 2008 K. Kumar

SAMPLE Experiment Caltech, Illinois, Kentucky, LaTech, Maryland, MIT, Virginia Tech, W&M Z Measure G M (Q 2 = 0.1 GeV 2 ) • for 1 H, 2 H E beam = 200 MeV I beam = 40 μ A P beam = 35% Δθ = 130 - 170 o ΔΩ = 1.5 sr l target = 40 cm L = 4.3 x 10 38 cm -2 s -1 A ~ -7 ppm

HAPPEx (JLab Hall A) s + 0.39 G M s at • Measured G E Q 2 = 0.48 GeV 2 Pb-Sci Calorimeters HRS Spectrometers Electron Beam LH 2 Target 2004 runs: 1 H, 4 He at 0.11 GeV 2 • E beam = 3.2 GeV 10 Asymmetry (ppm) I beam ~ 50 μ A 5 P beam = 80% 0 θ = 6 0 -5 ΔΩ = (3.7 msr) x 2 -10 l target = 20 cm L = ~2 x 10 38 cm -2 s -1 0 1 2 3 4 5 6 Data Set Number A ~ -2, +8 ppm HAPPEx nucl-ex/0506010

PVA4 (Mainz) s + 0.11 G M s at Q 2 = 0.1 GeV 2 • Measure G E – have also measured at Q 2 = 0.23 GeV 2 Second measurement E beam = 0.57 GeV I beam = 20 μ A P beam = 80% θ = 35 0 ΔΩ = 0.7 sr l target = 10 cm L = 0.5 x 10 38 cm -2 s -1 A ~ -2 ppm Counts Q 2 =0.1 GeV 2 • – A meas = -1.36 ± 0.29 ± 0.13 ppm – A th = -2.06 ± 0.14 ppm – PRL 94 (05) 152001 Channel

G0 Experiment (JLab Hall C) Z Z • Measure , G E G M E beam = 3.03 GeV, 0.36 - 0.69 GeV – different linear combination I beam = 40 μ A, 80 μ A of u , d and s contributions P beam = 75%, 80% θ = 52 – 76 0 , 104 - 116 0 than e.m. form factors ΔΩ = 0.9 sr, 0.5 sr → strange quark contributions l target = 20 cm L = 2.1, 4.2 x 10 38 cm -2 s -1 to sea A ~ -1 to -50 ppm, -12 to -70 ppm • Measure forward and backward asymmetries Superconducting – recoil protons for forward Particle Coils Detectors measurement – electrons for backward measurements Electron Beam • elastic/inelastic for 1 H, elastic for 2 H • Forward measurements LH 2 Target complete (101 Coulombs)

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

Results (Last Thursday)

Strange Quark Contribution • Strange quark contribution to asymmetry 2 2 πα ε + τ ( ) p p 4 2 G G + = − η s s ( ) E M G G A A ε + E M phys NVS 2 p ( 0 ) G Q G 1 R F E V τ ( ) p G η = 2 M Q , E ε i p G E http://www.npl.uiuc.edu/exp/G0/Forward

G0 Experimental Asymmetries s s G E • “no vector strange” asymmetry, A NVS , is A( , = 0) G M – 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 to Proton http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001

Det 1-14 Background Correction ( ) Det 8 = 1 − + A f A f A meas el back • Results of 2-step fitting procedure: det 8 – fit Y back (poly’ l of degree 4), Gaussian for elastic peak – then fit A back (poly’ l of degree 2), constant A el • asym: χ 2 = 37.5/44 – f determined from Y back , Y meas in subsequent analysis • don’t use detailed shape of elastic peak • Det 14 similar except it has 2 elastic peaks – Q 2 = 0.41, 1.0 GeV 2

Det. 1-14 Background Uncertainty • Background yield shape varied Det 8 within “lozenge” – use a variety of shapes • Similar approach for asymmetry shape – vary throughout range • Then for each pair of shapes Y = back f Y meas ( ) ~ = − + A 1 f A fA meas el back ~ distribution of gives A el systematic uncertainty

s G M s . G E , Data @ Q 2 = 0.1 GeV 2 s G E = -0.013 ± 0.028 s = +0.62 ± 0.31 G M Contours 1 σ , 2 σ 68.3, 95.5% CL Theories 1. Leinweber, et al. PRL 94 (05) 212001 2. Lyubovitskij, et al. PRC 66 (02) 055204 3. Lewis, et al. PRD 67 (03) 013003 4. Silva, et al. PRD 65 (01) 014016 http://www.npl.uiuc.edu/exp/G0/Forward

s G M s . G E , Data @ Q 2 = 0.1 GeV 2 s G E = -0.013 ± 0.028 s = +0.62 ± 0.31 G M p (0.1 GeV 2 ) = 2.12: G M u: 2.28 ± 0.21 d: 0.03 ± 0.11 s: -0.21 ± 0.11 n (0.1 GeV 2 ) = -1.42: G M u: -0.07 ± 0.11 d: -1.14 ± 0.21 s: -0.21 ± 0.11 http://www.npl.uiuc.edu/exp/G0/Forward

Results (Today)

1 H Preliminary Results Asymmetry (ppm) Raw Parity Violating Asymmetry ~25 M pairs, width ~540 ppm A raw correction ~11 ppb Helicity Window Pair Asymmetry Slug Q 2 = 0.1089 ± 0.0011GeV 2 A raw = -1.418 ppm ± 0.105 ppm (stat)

4 He Preliminary Results Raw Parity Violating Asymmetry Asymmetry (ppm) 35 M pairs, total width ~1130 ppm A raw correction ~ 0.12 ppm Helicity Window Pair Asymmetry Slug Q 2 = 0.07725 ± 0.0007 GeV 2 A raw = 5.253 ppm ± 0.191 ppm (stat)

HAPPEX-II 2005 Preliminary Results HAPPEX- 4 He: Q 2 = 0.0772 ± 0.0007 (GeV/c) 2 A PV = +6.43 ± 0.23 (stat) ± 0.22 (syst) ppm A(G s =0) = +6.37 ppm G s E = 0.004 ± 0.014 (stat) ± 0.013 (syst) HAPPEX-H: Q 2 = 0.1089 ± 0.0011 (GeV/c) 2 A PV = -1.60 ± 0.12 (stat) ± 0.05 (syst) ppm A(G s =0) = -1.640 ppm ± 0.041 ppm G s E + 0.088 G s M = 0.004 ± 0.011 (stat) ± 0.005 (syst) ± 0.004 (FF)

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 Preliminary Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account

World Data near Q 2 ~0.1 GeV 2 s = 0.28 +/- 0.20 G M s = -0.006 +/- 0.016 G E ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of Electric distribution HAPPEX-only fit suggests something even smaller: s = 0.12 +/- 0.24 G M Preliminary s = -0.002 +/- 0.017 G E Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account

World Data near Q 2 ~0.1 GeV 2 s = 0.28 +/- 0.20 G M p (0.1 GeV 2 ) = 2.12: G M u: 2.06 ± 0.14 d: 0.15 ± 0.07 s: -0.09 ± 0.07 n (0.1 GeV 2 ) = -1.42: G M Preliminary u: -0.29 ± 0.07 d: -1.03 ± 0.14 s: -0.09 ± 0.07

Speculation