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Strangeness in the Nucleon

Strangeness in the Nucleon. Kent Paschke University of Massachusetts. EINN ‘05 September 24, 2005. Strange Quarks in the Nucleon. Strange Sea measured in n N scattering. Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled. Spin polarized DIS

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Strangeness in the Nucleon

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  1. Strangeness in the Nucleon Kent Paschke University of Massachusetts EINN ‘05 September 24, 2005

  2. Strange Quarks in the Nucleon Strange Sea measured in nN scattering Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled • Spin polarized DIS • Inclusive: Ds = -0.10 ± 0.06 • uncertainties from SU(3), extrapolation • Semi-inclusive: Ds = 0.03± 0.03 • fragmentation function • Strange mass • pN scattering: ~30% Strange vector FF Kent Paschke – University of Massachusetts

  3. Flavor Separation of Nucleon Form Factors (assumes heavy quarks are negligible) Measuring cannot separate all three flavors Adding in a measurement of and assuming charge symmetry then we can write Kent Paschke – University of Massachusetts

  4. Accessing Weak Neutral Current Amplitude Longitudinal spin asymmetry violates parity (polarized e-, unpolarized p): Interference with EM amplitude makes NC amplitude accessible Kent Paschke – University of Massachusetts

  5. Backward angle Forward angle Parity-violating electron scattering For a proton: ~ few parts per million For 4He:GEs alone(but only available at low Q2) For deuterium: enhanced GAe sensitivity Kent Paschke – University of Massachusetts

  6. Instrumentation for PVES • Need • Highest possible luminosity • High rate capability • High beam polarization • Large -Acceptance Detectors (G0, A4) • Large kinematic range • Large Detected Background • Spectrometer (HAPPEx) • Good background rejection • Small solid angle Detectors Integrating (HAPPEx) vs. Counting (G0, A4) • Cumulative Beam Asymmetry • Helicity-correlated asymmetry • Dx~10 nm, DI/I~1 ppm, DE/E~100 ppb • Helicity flips • Fast: Pockels cell • Slow: half-wave plate flips Kent Paschke – University of Massachusetts

  7. Polarized Electron Source Optical Pumping HV Extraction and Injection • Beam helicity is chosen pseudo-randomly at 30 Hz • Helicity state, followed by its complement • Data analyzed as “pulse-pairs” calculated at 15Hz Kent Paschke – University of Massachusetts

  8. Controlling Systematic Uncertainty • Normalization • Polarimetry – continuous measurement/monitoring. Control of systematic error • Linearity/Deadtime • Background Dilution • False Asymmetries • Beam Asymmetries – Source laser control, careful measurement and correction • Electronics pickup • Background Asymmetries HAPPEX: Polarization monitored continuously with a Compton polarimeter. (Average ~88% with superlattice photocathode.) Polarimetry is dominant systematic error in two recent experiments Kent Paschke – University of Massachusetts

  9. Experimental Overview A4 SAMPLE Open geometry Fast counting calorimeter for background rejection open geometry, integrating GEs + 0.23 GMs at Q2 = 0.23 GeV2 GEs + 0.10 GMs at Q2 = 0.1 GeV2 GMs, (GA) at Q2 = 0.1 GeV2 HAPPEX GEs + 0.39 GMs at Q2 = 0.48 GeV2 GEs + 0.08 GMs at Q2 = 0.1 GeV2 GEs at Q2 = 0.1 GeV2 (4He) G0 Precision spectrometer, integrating Open geometry Fast counting with magnetic spectrometer + TOF for background rejection GEs + hGMs over Q2 = [0.12,1.0] GeV2 GMs, GAe at Q2 = 0.3, 0.5, 0.8 GeV2 Kent Paschke – University of Massachusetts

  10. GsM(Q2=0.1) = 0.37  0.20  0.26  0.07 SAMPLE at MIT-Bates Measure GMs at Q2 ~0.1 GeV2 Backward angle, H and 2H at low Q2 Air Cerenkov detector covers 2 sr from 130°-170° Analog integrating electronics for asymmetry measurement Pulse-Counting for background studies Theory prediction for anapole moment radiative correction. Result of Zhu et al for GA commonly used to constrain GSM result. Kent Paschke – University of Massachusetts

  11. GEs + 0.39 GMs at Q2 =0.48 GeV2 • High Resolution Spectrometerseliminate background • Analog integration of Cerenkov calorimeter for asymmetry measurement • Tracking for background/kinematics studies HAPPEx-I in Hall A Kent Paschke – University of Massachusetts

  12. Brass-Quartz integrating detector Background ≤ 3% PMT Elastic Rate: 1H: 120 MHz Cherenkov cones 4He: 12 MHz PMT HAPPEX-II: 1H and 4He 3 GeV beam in Hall Alab ~ 6Q2 ~ 0.1 GeV2 Septum magnets (not shown) High Resolution Spectrometers detectors Hall A at Jlab Kent Paschke – University of Massachusetts

  13. Hydrogen 4He Helicity Window Pair Asymmetry 2004 HAPPEX-II Data • Short run (~ 5 days) • Beam Polarization ~ 86% • Beam asymmetries small • Background f <3% • Dense gas target Araw correction < 0.2 ppm Araw = + 5.63 ppm ± .71 ppm (stat) Raw Asymmetry(after beam corrections) • ~1/2 proposed time • Beam asymmetries small • Araw correction ~ 0.06 ppm • Background f ~1% • Beam Polarization ~ 80% ppm Perfect sign-flip with /2 plate Araw = -0.95 ppm ± 0.20 ppm (stat) Kent Paschke – University of Massachusetts

  14. PVA4 at Mainz • MAMI Microtron, 2000-present • GEs + h GMs at Q2 = 0.23, 0.1 GeV2 • Calorimeter distinguishes elastic via energy resolution, 0.8 sr from 30° to 40° • Elastic rate: 10 MHz, total rate 100 MHz Calorimeter: 1022 PbF2 crystals LuMo 20 cm LH2 target 20 mA, 80% polarized beam Kent Paschke – University of Massachusetts

  15. G0 Experiment in Hall C Ebeam = 3.03 GeV, 0.33 - 0.93 GeV Ibeam = 40 A, 80 A Pbeam = 75%, 80%  = 52 – 760, 104 - 1160  = 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 • Measure forward and backward asymmetries • recoil protons for forward measurement: GEs, GMs • electrons for backward measurements: GMs, GAe • Fast Counting/Magnetic spectrometer Forward measurements complete (2004) Back-angle measurements scheduled - 2006 Kent Paschke – University of Massachusetts

  16. G0 Forward-angle Measurement • Acceptance Q2=[0.12, 1.0] GeV2 for 3 GeV incident beam • Time-of-flight measured over 32 ns beam bunch spacing • Detector 15 acceptance: Q2=[0.44,0.88] GeV2 subdivided by TOF elastic protons detectors lead collimators target beam • TOF used to ID elastic recoil protons • Measurement of yield and asymmetry of spectrum used to deduce background fraction and asymmetry Hear more tomorrow from Benoit Guillon Kent Paschke – University of Massachusetts

  17. G0 Backward Angle • Electron detection • Turn magnet/detector package around • Add Cryostat Exit Detectors (“CEDs”) to define electron trajectory • Add aerogel Cerenkovs to reject pions Begin Backward Angle installation in 2005 Planned measurements of H, 2H Q.E. Combine with forward angle to separate GsE, GsM, GA at 2 or 3 Q2 points Likely to run in 2006 at Q2~0.3 GeV2, Q2~0.8 GeV2 Kent Paschke – University of Massachusetts

  18. Results Kent Paschke – University of Massachusetts

  19. Extrapolated from G0 Q2=[0.12,0.16] GeV2 Dc2 = 1 95% c.l. World Data at Q2 ~ 0.1 GeV2 Note: excellent agreement of world data set GEs = -0.12 ± 0.29 GMs = 0.62 ± 0.32 Would imply that 7% of nucleon magnetic moment is Strange Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account Kent Paschke – University of Massachusetts

  20. Perspective at Q2 ~ 0.1 GeV2 • Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992). • Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996). • Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999). • Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001). • Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002). • Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003). • Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005). L-K oscillation of proton would produce a positive GEs Kent Paschke – University of Massachusetts

  21. Anticipated Results from HAPPEX-II 2-3X improvement for each HAPPEX measurement • Result matching current central value: • would convincingly establish a non-zero result • would find GMs ~3s from zero Experiment Running NOW Results available (early?) 2006 Q2 ~ 0.1 GeV2 Kent Paschke – University of Massachusetts

  22. Global error accounts for large background corrections • f ~5-20% • DA/ANVS ~40-60% G0 Forward - Measured Asymmetries • “no vector strange” asymmetry, ANVS, is A(GEs, GMs = 0) • inside error bars: stat, outside: stat & pt-pt Kent Paschke – University of Massachusetts

  23. World Forward-angle Hydrogen Data • G0 Results are big news: • Amplifies interesting low Q2 structure • Strong constraint at Q2~0.2 GeV2 • Significant non-zero result at higher Q2 G0 (h ~ Q2) Kent Paschke – University of Massachusetts

  24. Possible interpretation of G0 results • Fit world data set with dipole form for GMs and GEn-like behavior for GEs • If not a statistical fluctuation, data implies large value of s and strong Q2-variation of GEs • Will be addressed by future measurements Kent Paschke – University of Massachusetts

  25. Future HAPPEx run • PAC28 last month conditionally approved a new HAPPEx proposal to run at ~0.6 GeV2 to obtain an unprecedented precision (2007?) • Requires 1% polarimetry Kent Paschke – University of Massachusetts

  26. G0 Backward HAPPEX-III GEs 0.6 GeV2 GMs Prospective JLab Data @ Q2 = 0.6, 0.23 GeV2 • G0 Run in March ’06 at Q2 = ~0.6 GeV2 • G0 Run in Summer of ‘06 at Q2 = ~0.23 GeV2 • HAPPEX-III Run at Q2 = ~0.6 GeV2 (not before 2007) • Also, A4 at 0.23 GeV2 or 0.5 GeV2? Kent Paschke – University of Massachusetts

  27. G0 backward HAPPEX-III GEs 0.6 GeV2 GMs Summary • Suggested large values at Q2~0.1 GeV2 • HAPPEX-II, H and He running now! • Large possible cancellation at Q2~0.2 GeV2 • G0 backangle, conditionally approved for Summer ’06 • A4 backangle? • Possible large values at Q2>0.4 GeV2 • G0 backangle, approved for Spring ’06 • HAPPEX-III, conditionally approved - 2007? • A4 backangle? Kent Paschke – University of Massachusetts

  28. Transverse Asymmetry Kent Paschke – University of Massachusetts

  29. “elastic” “inelastic” Interest in AT AT is T-odd, P-even • As a radiative correction, it is similar to other T-odd QED FSI that obscure measurements of nuclear g-decay, neutron b-decay, or other searches for T-odd, P-even interactions. Probe of nucleon structure • Doubly virtual Compton scattering (VVCS) constrains interpretation from DVCS Dominated by spectrum of hadronic intermediate states • Provides a clear and accessible window on the treatment of hadronic intermediate states in box diagrams. GE/GM is influenced by the real part of 2-g amplitude. AT is generated from the imaginary part of the 2-g amplitude. Kent Paschke – University of Massachusetts

  30. A4 AT Data from 0.2 GeV-3 GeV Pasquini & Vanderhaeghen Resonance region treated in a model incorporating pion electroproduction amplitudes “single pion” hep-ph/0405303 sum “elastic” SAMPLE P&VdH • Optical theorem: relate to tot((*)p) • Low Q2 and very forward angle • At fixed Q2, flat with energy HAPPEX (prelim) Afanasev and Merenkov, hep-ph/0406127 Kent Paschke – University of Massachusetts

  31. AT at E158 f (Azimuthal angle) 46 GeV ep  ep Sign: AT<0 Q2 ~ 0.06 GeV2 Magnitude: ~2.5 ppm Without enhancement by inelastic states, ATep ~ 10-10 46 GeV ee  ee Magnitude: ~3.5 ppm backward angle Sign: opposite ATep? Kent Paschke – University of Massachusetts

  32. AT from Nuclei Afanasev Predicted value, ~10-5 at 6 degrees, 3 GeV Without inelastic states, 10-9 Kent Paschke – University of Massachusetts

  33. Backup Kent Paschke – University of Massachusetts

  34. World Data at Q2 ~ 0.1 GeV2 Extrapolated from G0 Q2=[0.12,0.16] GeV2 Dc2 = 1 GEs = -0.020 ± 0.030 GMs = 0.72 ± 0.40 95% c.l. Kent Paschke – University of Massachusetts

  35. LQCD prediction for s with Charge Symmetry • Use charge symmetry to relate valence quark magnetic dipole moments and loop contributions • Use Lattice QCD only to calculate ratios of valence quark magnet dipole moments • LQCD results in excellent agreement with measured octet magnetic moments Leinweber et al. PRL 94, 212001 (2005) Lattice calculation ms = -(0.046  0.019)mN Kent Paschke – University of Massachusetts

  36. Strange Vector FF and Lattice QCD Lattice - Lewis, Wilcox & Woloshyn PRD 67, 013003 (2003) Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001). Kent Paschke – University of Massachusetts

  37. Electromagnetic FF Axial FF (GAZ) Extraction of SVFF from APV Including radiative corrections, APV from hydrogen is: Axial FF: d(APV) = 0.33 ppm EMFF: dominated by GnM, d(APV) = 0.53 ppm Total: d(APV) =0.62 ppm, 2.8% Kent Paschke – University of Massachusetts

  38. d(GAZ) ~ 0.14 Axial Form Factor Axial Form Factor: Uncertainty dominated by “anapole moment” Assume dipole FF, with MA = 1.001 GeV d(GAZ) ~ 0.12, d(APV) = 0.33 ppm Compatible with Phys. Rev. C 69, 065501 (2004) [Zhu et al , 2000] [Maekawa et al , 2000] E04-115 G0 Backward Angle Kent Paschke – University of Massachusetts

  39. EM Form Factors But: 2-photon effects can complicate this picture at 2-4% level Experimental constraint: E04-116 in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q2 Kent Paschke – University of Massachusetts

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