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

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Physics Motivation
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Strange Quark Observables

• scalar matrix element
• .
• see talk by M. Sainio, Th. 245
• 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. 230)
• vector matrix elements (Mon. 230)

CTEQ6M, NLO NuTEV hep-ex/0405037
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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

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. , Non-Zero?

• 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

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Parity-Violating Electron Scattering

• contributes to electron scattering
• - interference term large x small

• Interference term violates parity
  usewhere

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Experiments
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Summary of PV Electron Scattering Experiments
publishing, running
publishing, running
2006
published x2, running
published, running
2008
K. Kumar
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SAMPLE Experiment
Caltech, Illinois, Kentucky, LaTech, Maryland,
MIT, Virginia Tech, WM

• 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
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HAPPEx (JLab Hall A)

• 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
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PVA4 (Mainz)

• 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

• Q20.1 GeV2
• Ameas -1.36 0.29 0.13 ppm
• Ath -2.06 0.14 ppm
• PRL 94 (05) 152001

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G0 Experiment (JLab Hall C)

• 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
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G0 in Hall C (JLab)
superconducting magnet (SMS)
cryogenic supply
beam monitoring girder
scintillation detectors
cryogenic target service module
electron beamline
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Results
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G0 Experimental Asymmetries

• 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
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Strange Quark Contribution

• Strange quark contribution to asymmetry

http//www.npl.uiuc.edu/exp/G0/Forward
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Strange Quark Contribution to Proton
http//www.npl.uiuc.edu/exp/G0/Forward
D. Armstrong, et al. PRL 95 (2005) 092001
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. , Data _at_ Q2 0.1 GeV2
-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
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. , Data _at_ Q2 0.1 GeV2
-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
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Speculation
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Simple Fits to All Hydrogen Data

• Fit

with simple forms for ,
à la Kelly
with
from Q2 0.1 GeV2 result, dipole ff
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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
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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

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Remember the factor of -1/3
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Future Running Separation of , .

• 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 lt 0??
• can run H D for Q2 lt 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 lt 0??
• conditionally approved

s

s
s
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Summary

• Parity-violating elastic electron scattering
  measures strange quark vector currents
• Four new forward angle results in 2005
• PVA4 H _at_ Q2 0.1 GeV2
• HAPPEx H _at_ Q2 0.1 GeV2
• HAPPEx He _at_ Q2 0.1 GeV2
• G0 H _at_ Q2 0.1 1 GeV2
• Results self-consistent
• Emerging picture
• GM gt 0 at low Q2 - likely
• some cancellation of GE and GM likely
• hint that GE lt 0 at medium Q2

s
s
s
s