Strangeness in the NucleonKent PaschkeUniversity of MassachusettsEINN 05September 24, 2005

Strange Quarks in the NucleonStrange Sea measured in nN scatteringSpin polarized DISInclusive: Ds = -0.10 0.06 uncertainties from SU(3), extrapolationSemi-inclusive: Ds = 0.03 0.03 fragmentation functionStrange vector FFStrange masspN scattering: ~30% Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled

Flavor Separation of Nucleon Form FactorsMeasuringcannot separate all three flavors(assumes heavy quarks are negligible)Adding in a measurement of and assuming charge symmetrythen we can write

Accessing Weak Neutral Current AmplitudeInterference with EM amplitude makes NC amplitude accessibleLongitudinal spin asymmetry violates parity (polarized e-, unpolarized p):

Parity-violating electron scattering~ few parts per millionFor a proton:For 4He: GEs alone (but only available at low Q2)For deuterium: enhanced GAe sensitivity

Instrumentation for PVESLarge -Acceptance Detectors (G0, A4)Large kinematic rangeLarge Detected BackgroundSpectrometer (HAPPEx)Good background rejectionSmall solid angleCumulative Beam AsymmetryHelicity-correlated asymmetryDx~10 nm, DI/I~1 ppm, DE/E~100 ppb Helicity flipsFast: Pockels cellSlow: half-wave plate flipsNeedHighest possible luminosityHigh rate capabilityHigh beam polarizationDetectorsIntegrating (HAPPEx) vs. Counting (G0, A4)

Polarized Electron Source Beam helicity is chosen pseudo-randomly at 30 HzHelicity state, followed by its complementData analyzed as pulse-pairsOptical PumpingHV Extraction and Injectioncalculated at 15Hz

Controlling Systematic UncertaintyHAPPEX: Polarization monitored continuously with a Compton polarimeter.

(Average ~88% with superlattice photocathode.)False Asymmetries Beam Asymmetries Source laser control, careful measurement and correction Electronics pickup Background AsymmetriesNormalization Polarimetry continuous measurement/monitoring. Control of systematic error Linearity/Deadtime Background DilutionPolarimetry is dominant systematic error in two recent experiments

Experimental OverviewGMs, (GA) at Q2 = 0.1 GeV2SAMPLEHAPPEXGEs + 0.39 GMs at Q2 = 0.48 GeV2GEs + 0.08 GMs at Q2 = 0.1 GeV2GEs at Q2 = 0.1 GeV2 (4He)Precision spectrometer, integratingA4open geometry, integratingGEs + 0.23 GMs at Q2 = 0.23 GeV2GEs + 0.10 GMs at Q2 = 0.1 GeV2Open geometryFast counting calorimeter for background rejectionG0GEs + h GMs over Q2 = [0.12,1.0] GeV2GMs, GAe at Q2 = 0.3, 0.5, 0.8 GeV2Open geometryFast counting with magnetic spectrometer + TOF for background rejection

SAMPLE at MIT-BatesMeasure GMs at Q2 ~0.1 GeV2 Backward angle, H and 2H at low Q2Air Cerenkov detector covers 2 sr from 130-170Analog integrating electronics for asymmetry measurementPulse-Counting for background studiesTheory prediction for anapole moment radiative correction.Result of Zhu et al for GA commonly used to constrain GSM result.

HAPPEx-I in Hall A GEs + 0.39 GMs at Q2 =0.48 GeV2 High Resolution Spectrometers eliminate background Analog integration of Cerenkov calorimeter for asymmetry measurement Tracking for background/kinematics studies

HAPPEX-II: 1H and 4He3 GeV beam in Hall A lab ~ 6 Q2 ~ 0.1 GeV2Septum magnets (not shown) High Resolution Spectrometers detectors Hall A at Jlab

targetAPVGs = 0 (ppm)Stat. Error (ppm)Syst. Error (ppm)sensitivity(proposed)1H-1.60.080.04(GEs+0.08GMs) = 0.0104He+7.80.180.18(GEs) = 0.015

2004 HAPPEX-II DataAraw = + 5.63 ppm .71 ppm (stat)Short run (~ 5 days)Beam Polarization ~ 86%Beam asymmetries small

Background f

PVA4 at MainzCalorimeter:1022 PbF2 crystals20 cm LH2 target20 mA, 80% polarized beamLuMoMAMI 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

G0 Experiment in Hall CMeasure forward and backward asymmetriesrecoil protons for forward measurement: GEs, GMselectrons for backward measurements: GMs, GAeFast Counting/Magnetic spectrometer

Forward measurements complete(2004)

Back-angle measurements scheduled - 2006Ebeam = 3.03 GeV, 0.33 - 0.93 GeVIbeam = 40 A, 80 APbeam = 75%, 80% = 52 760, 104 - 1160 = 0.9 sr, 0.5 srltarget = 20 cmL = 2.1, 4.2 x 1038 cm-2 s-1A ~ -1 to -50 ppm, -12 to -70 ppm

G0 Forward-angle Measurementlead collimatorselastic protonsdetectorstargetbeam TOF used to ID elastic recoil protons

Measurement of yield and asymmetry of spectrum used to deduce background fraction and asymmetryAcceptance 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

Hear more tomorrow from Benoit Guillon

G0 Backward AngleElectron detectionTurn magnet/detector package aroundAdd Cryostat Exit Detectors (CEDs) to define electron trajectoryAdd aerogel Cerenkovs to reject pions Begin Backward Angle installation in 2005Planned measurements of H, 2H Q.E.

Combine with forward angle to separate GsE, GsM, GA at 2 or 3 Q2 pointsLikely to run in 2006 at Q2~0.3 GeV2, Q2~0.8 GeV2

Results

World Data at Q2 ~ 0.1 GeV2 GEs = -0.12 0.29GMs = 0.62 0.32Would imply that 7% of nucleon magnetic moment is StrangeNote: excellent agreement of world data setCaution: the combined fit is approximate. Correlated errors and assumptions not taken into account

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

Anticipated Results from HAPPEX-II2-3X improvement for each HAPPEX measurement Q2 ~ 0.1 GeV2Experiment Running NOW Results available (early?) 2006Result matching current central value: would convincingly establish a non-zero result would find GMs ~3s from zero

G0 Forward - Measured Asymmetriesno vector strange asymmetry, ANVS, is A(GEs, GMs = 0)inside error bars: stat, outside: stat & pt-pt

World Forward-angle Hydrogen Data(h ~ Q2)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

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

Future HAPPEx runPAC28 last month conditionally approved a new HAPPEx proposal to run at ~0.6 GeV2 to obtain an unprecedented precision (2007?)

Requires 1% polarimetry

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?

Summary Suggested large values at Q2~0.1 GeV2 HAPPEX-II, H and He running now! Possible large values at Q2>0.4 GeV2 G0 backangle, approved for Spring 06 HAPPEX-III, conditionally approved - 2007? A4 backangle? Large possible cancellation at Q2~0.2 GeV2 G0 backangle, conditionally approved for Summer 06 A4 backangle?

Transverse Asymmetry

Interest in ATAT is T-odd, P-evenAs 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 structureDoubly virtual Compton scattering (VVCS) constrains interpretation from DVCS

Dominated by spectrum of hadronic intermediate statesProvides 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.

AT Data from 0.2 GeV-3 GeVSAMPLEelasticsingle pionsumhep-ph/0405303Pasquini &VanderhaeghenResonance region treated in a model incorporating pion electroproduction amplitudesP&VdHHAPPEX (prelim)Afanasev and Merenkov,hep-ph/0406127 Optical theorem: relate to tot((*)p) Low Q2 and very forward angle At fixed Q2, flat with energy

AT at E158f(Azimuthal angle)46 GeVep epSign: AT

AT from NucleiAfanasevWithout inelastic states, 10-9Predicted value, ~10-5 at 6 degrees, 3 GeV

Backup

World Data at Q2 ~ 0.1 GeV2 Extrapolated from G0 Q2=[0.12,0.16] GeV295% c.l.Dc2 = 1GEs = -0.020 0.030GMs = 0.72 0.40

LQCD prediction for s with Charge SymmetryLeinweber et al.PRL 94, 212001 (2005)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 momentsms = -(0.046 0.019)mNLattice calculation

Strange Vector FF and Lattice QCDLattice - Lewis, Wilcox & WoloshynPRD 67, 013003 (2003)Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).

Extraction of SVFF from APVIncluding radiative corrections, APV from hydrogen is:Axial FF: d(APV) = 0.33 ppm EMFF: dominated by GnM, d(APV) = 0.53 ppmTotal: d(APV) = 0.62 ppm, 2.8%

Axial Form FactorAxial Form Factor: Uncertainty dominated by anapole moment[Zhu et al , 2000]Assume dipole FF, with MA = 1.001 GeVd(GAZ) ~ 0.12, E04-115 G0 Backward AngleCompatible with Phys. Rev. C 69, 065501 (2004)[Maekawa et al , 2000]d(APV) = 0.33 ppm

EM Form FactorsBut: 2-photon effects can complicate this picture at 2-4% levelExperimental constraint:E04-116 in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q2

uncertaintyd(APV)/APVGpM2%negligibleGpE1.5%0.24 ppmGnE8%0.26 ppmGnM2%0.44 ppmTotal0.53 ppm

Supplementary