The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

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  • The G0 ExperimentParity-violating electron scattering from the nucleonLongitudinal beam polarizationStrange quark contribution to elastic form factorsEffective axial-vector elastic form factorAxial-vector N-D transitionWeak interaction contribution to pion photoproduction

    Single-spin asymmetriesTransverse beam polarization2g contribution to elastic scattering(Single spin asymmetry in pion photoproduction)

    D. BeckMar. 2012

  • Strange Quark Observablesscalar matrix element.

    momentum carried by strange quarks. NuTEV hep-ex/9906037. spin carried by strange quarksas determined in sum ruleDs ~ -0.1 - 0as determined in semi-inclusive Ds(x)

    vector matrix elementsHERMES: Phys. Rev. D 89 (2014) 097101S. Alekhin et al. arXiv:1404.6469

  • Parity-Violating Electron ScatteringInterference term violates parity: use where contributes to electron scattering

    - interference term: large x smallepZ

  • Quark Currents in the NucleonMeasure e.g. note then charge symmetry (see B. Kubis & R. Lewis, PRC 74 (06) 015204 and G. A. Miller PRC 57 (98) 1492.)

    dropping the p superscripts on the left

  • California Institute of Technology, Carnegie Mellon University, College of William and Mary, Grinnell College, Hampton University, Hendrix College, Institut de Physique Nuclaire d'Orsay, J. Stefan Institute, Laboratoire de Physique Subatomique et de Cosmologie-Grenoble, Louisiana Tech University, New Mexico State University, Ohio University, Thomas Jefferson National Accelerator Facility, TRIUMF, University of Illinois, University of Kentucky, University of Manitoba, University of Maryland, University of Northern British Columbia, University of Winnipeg, University of Zagreb, Virginia Tech, Yerevan Physics InstituteG0 CollaborationGraduate Students:C. Capuano (2011 W&M), A. Coppens (2010 Manitoba), C. Ellis (2010 Maryland), J. Mammei (2010 VaTech), M. Muether (2010 Illinois), J. Schaub (2010 New Mexico State), M. Versteegen (2009 Grenoble); S. Bailey (2007 W&M)

    Analysis Coordinator:F. Benmokhtar - Carnegie Mellon (Maryland)

    SUPPORT: DOE, NSF, IN2P3, NSERC Thank-you!

  • G0 Collaboration

  • G0 Experiment OverviewMeasure ,different linear combination of u, d and s contributions than e.m. form factorsstrange quark contributions to sea (few % of overall Gs)Measure forward and backward asymmetriesrecoil protons for forward measurementelectrons for backward measurementselastic/inelastic for 1H, quasi-elastic for 2HEbeam = 3.03 GeV, 0.33 - 0.93 GeVIbeam = 40 mA, 80 mAPbeam = 75%, 80%q = 52 760, 104 - 1160DW = 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 in Hall Cbeammonitoring girdersuperconducting magnet (SMS)scintillation detectorscryogenic supplycryogenic target service moduleelectron beamline

  • What Do We See?Different components separated by t.o.f.

    Background under elastic peak is main analysis issueBackground correction involves dilution factor, f and background asymmetry, Aback

  • Back Angle LayoutElastic, inelastic electron separation using FPD, CEDElectron/pion separation using aerogel CherenkovCherenkovElectron BeamCryostat Exit DetectorFocal PlaneDetectorShieldingCryotargetSingle Octant Schematic

  • Back Angle ApparatusBack angle detector packageTarget system installationFPDCEDCherenkovSuperconductingMagnet

  • LH2, 678 MeV LH2, 687 MeV LH2, 362 MeV LD2, 687 MeV LD2, 362 MeV Electron Yields(quasi) elastic electronsinelastic electronsbackground regions

  • Combined Results (2010)Using interpolation of G0 forward measurementsAndroi, et al. PRL 104 (2010) 012001

  • HAPPEx III ResultZ. Ahmed, et al. PRL 108 (2012) 102001Q2 = 0.62 GeV2

  • Relative to Overall Form FactorsZ. Ahmed, et al. PRL 108 (2012) 102001

  • Combined Results with TheoryAndroi, et al. PRL 104 (2010) 012001

  • PV: Inelastic Scattering/Pion ProductionN-D transitionDominant magnetic dipole (M1) transition in photoproductionCoupling to vector currentCorresponds roughly to quark spin flip (via magnetic moment)Also study spin flip in axial currente.g. charged pion electroproduction ep ep-D++ A. Liesenfeld et al , Phys. Lett. B468 (1999) 20.Pure spin flip accompanied by flavor changeWe measure neutral current coupling to nucleon axial transition current: APV(inel)Like electroproduction, different flavor structure

    Pion productionMeasure inclusive p- from D target, dominated by photoproductionAsymmetry at Q2 =0 not zero (current conservation)dD related to the anomalous DS = 1 hyperon decays S.-L. Zhu, C. Maekawa, B. Holstein & M. Ramsey-Musolf PRL 87 (2001) 201802

  • Inelastic AsymmetryC. Capuano (thesis, W&M, 2011)ProtonDeuteron: A = -43.614.66.2 ppm

  • Pion AsymmetriesConstrain small photoproduction asymmetry dD(OUT IN)/2 = -0.56 1.03 ppm[OUT + IN = 3.84 2.15 ppm]A. Coppens (thesis, Manitoba, 2010), arXiv:1112.1720, PRL 108 (2012) 122002

  • Transverse AsymmetriesElastic scatteringSecond order e.m. effects generate single-spin asymmetriesEasy to measure with PV apparatus Pion productionInclusive pion yield also has azimuthal dependenceInvolves longitudinal/transverse interference (5th structure fn.)Suppressed by ~me/ECalculation by A. Afanasev, et al.; T. S. H. Lee, et al.Pasquini & Vanderhaeghen PRC 70 (2004) 045206Interference of 1g and 2g amplitudes; time reversal invariance requires An to involve the imaginary part of M2gReal part of M2g related to important contribution to longitudinal scattering: GE/GM ratio Ei = 570 MeV

  • Preliminary Transverse Asymmetries

  • Comparison of G0 Results with TheoryProtonJ. Mammei (thesis, VT, 2010), Androi, et al. PRL 107 (2011) 022501Neutron: Bn(362 MeV) = +8741 ppm (sign from GM)

  • Preliminary Pion Transverse AsymmetryA. Coppens (Manitoba)

  • SummaryComparison of electromagnetic and weak neutral elastic form factors allows determination of strange quark contributionlarge distance scale dynamics of the seaContributions of and less than few % over measured rangewhy s, sbar not separated? First measurements of neutral current ND transition around Q2 = 0.3 GeV2First measurements of PV asymmetry in inclusive p- production at low Q2 large dD ruled outFirst measurements of transverse asymmetries inback angle elastic scattering from H, D targets: Im(2g)Inclusive p- production: RLT

  • Another Holt MeasurementMDC ISO 400 gate valve has diameter of 16 in!

    *Generalize for F/B

    Remove?**Complete list with forward**No random subtraction in either LD2 spectrum*