Parity-Violating Electron Scattering & Charge Symmetry Breaking

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Parity-Violating Electron Scattering & Charge Symmetry Breaking. Krishna Kumar University of Massachusetts thanks to: C. Horowitz, T. Londergan, W. Marciano, G. Miller, M.J. Ramsey-Musolf, A. Thomas, B. van Kolck Workshop on Charge Symmetry Breaking Trento, June18, 2005. - PowerPoint PPT Presentation


  • Parity-Violating Electron Scattering & Charge Symmetry BreakingKrishna KumarUniversity of Massachusetts

    thanks to:C. Horowitz, T. Londergan, W. Marciano, G. Miller, M.J. Ramsey-Musolf, A. Thomas, B. van Kolck

    Workshop on Charge Symmetry BreakingTrento, June18, 2005In collaboration with: Kent Paschke (UMass)Paul Souder (Syracuse)Robert Michaels (Jlab)

  • OutlineParity-Violating Electron ScatteringDeep Inelastic ScatteringPhysics with 11 GeV ElectronsBeyond the Standard ModelSearch for Charge Symmetry Violationd/uTowards a 11 GeV ProgramElastic Electron-Nucleon ScatteringStrangeness in NucleonsRecent ResultsCharge Symmetry AssumptionOutlook

  • PV AsymmetriestoFor electrons scattering off nuclei or nucleons:Z couplings provide access to different linear combination of underlying quark substructure(gegT)

  • 2005: MeV to TeV Physics1970s1980s1990sRecent ResultsFutureResult Today! Steady progress in technology part per billion systematic control 1% normalization controlThree different avenues of investigation:Are there new interactions at very high energy?Do strange quarks in the nucleon affect its charge and magnetization distributions?How thick is the neutron skin in a heavy nucleus?GeV PhysicsTeV PhysicsMeV PhysicsValence quark structure of the nucleon: Jlab at 12 GeV

  • Electroweak Physics at Low Q2LEPII, Tevatron, LHC access scales greater than L ~ 10 TeVLogical to push to higher energies, away from the Z resonanceParity Conserving Contact InteractionsParity Violating Contact InteractionsQ2
  • Weak Neutral Current at low Q2Purely leptonic reaction QeW ~ 1 - 4sin2WZ0Fixed Target Mller Scattering

  • SLAC E158 Final Result hep-ex/0504049, To be published in PRL

  • Future Possibilities (Leptonic)-e in reactorSLAC E158can test neutrino coupling: sin2W to 0.002

  • Future Possiblities (Semileptonic)Qweak at Jlab measure sin2W to 0.0007 nail down fundamental low energy lepton-quark WNC couplings

    NuTeVAVVA C2is small & poorly known: difficult to measure in elastic scattering PV Deep inelastic scattering experiment with high luminosity 11 GeV beamAPV in elastic e-p scattering

  • Lepton Deep Inelastic Scattering b ~ 0.2 fm/sqrt(t) t=(p-p)2r ~ 0.2 fm/Q (0.02 0.2 fm for 100>Q2>1 GeV2) transverse size of probebCourtesey A. Caldwell

  • Parity Violating Electron DISfi(x) are quark distribution functionse-NXe-Z**For an isoscalar target like 2H, structure functions largely cancel in the ratio:Provided Q2 >> 1 GeV2 and W2 >> 4 GeV2 and x ~ 0.2 - 0.4Must measure APV to fractional accuracy better than 1% 11 GeV at high luminosity makes very high precision feasible JLab is uniquely capable of providing beam of extraordinary stability Systematic control of normalization errors being developed at 6 GeV

  • 2H Experiment at 11 GeVE: 5.0 GeV 10%lab = 12.5oAPV = 217 ppmIbeam = 90 A60 cm LD2 target Use both HMS and SHMS to increase solid angle ~2 MHz DIS rate, /e ~ 2-3xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2 Advantages over 6 GeV:Higher Q2, W2, f(y)Lower rate, better /eBetter systematics: 0.7%

  • Physics Implications

  • PV DIS and Nucleon StructureAnalysis assumed control of QCD uncertaintiesHigher twist effectsCharge Symmetry Violation (CSV)d/u at high xNuTeV provides perspectiveResult is 3 from theory predictionGenerated a lively theoretical debateRaised very interesting nucleon structure issues: cannot be addressed by NuTeVJLab at 11 GeV offers new opportunitiesPV DIS can address issues directlyLuminosity and kinematic coverageOutstanding opportunities for new discoveriesProvide confidence in electroweak measurement

  • Search for CSV in PV DISSensitivity will be further enhanced if u+d falls off more rapidly than u-d as x 1u-d mass differenceelectromagnetic effectsDirect observation of parton-level CSV would be very interestingImportant implications for high energy collider pdfsCould explain significant portion of the NuTeV anomaly

  • Potential Sensitivity

  • d(x)/u(x) as x1 Proton Wavefunction (Spin and Flavor Symmetric)

  • A New APV DIS Program2 to 3.5 GeV scattered electrons20 to 40 degreesFactor of 2 in Q2 rangeHigh statistics at x=0.7, with W>2

  • A PV DIS Program with upgraded JLabHydrogen and Deuterium targetsBetter than 2% errorsIt is unlikely that any effects are larger than 10%x-range 0.25-0.75W2 well over 4 GeV2Q2 range a factor of 2 for each x point(Except x~0.7)Moderate running timesCW 90 A at 11 GeV40 cm liquid H2 and D2 targetsLuminosity > 1038/cm2/s

  • Dynamics of Low Energy QCD( 0.2 fm)Profound qualitative and quantitative implications!

  • Strangeness in Nucleons?Breaking of SU(3) flavor symmetry introduces uncertainties

  • Electron Elastic Electroweak ScatteringParity Violating Amplitude dominated by NC terms:NC vector current probes same hadronic flavor structure, with different couplings:

  • Flavor Decomposed Form Factorscommonly used Sachs FF:Decompose by Quark Flavor:






    (1 + 4 sin2W




    1 ( 8/3 sin2W




    (1 + 4/3 sin2W


  • Charge Symmetry Charge symmetry: u-quark distribution in the proton is the same as the d-quark distribution in the neutron

  • How Big?

  • Elastic Electroweak MeasurementsAPV measurements ranging 0.1 < Q2 < 1forward and backward anglesHydrogen, Deuterium and Helium targetsStatistical and systematic errors < 10%Rough guide: GEn(Q2=0.2) ~ 0.05, ~ -0.6Cancellations? Q2 dependence? Accuracy?

  • HAPPEX at JLabThe HAPPEX Collaboration

    California State University, Los Angeles - Syracuse University -DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator Facility- INFN, Rome - INFN, Bari -Massachusetts Institute of Technology - Harvard University Temple University Smith College - University of Virginia - University of Massachusetts College of William and MaryHall A Proton Parity EXperiment1998-99: Q2=0.5 GeV2, 1H2004-05: Q2=0.1 GeV2, 1H, 4He

  • Spectrometers & DetectorsBeam diagnosticsQuadrupole magnetsBending magnetTargetSeptum magnetsComptonpolarimeter

  • 4He Asymmetry ResultQ2 = 0.091 (GeV/c)2 Araw = 5.63 ppm 0.71 ppm (stat)Araw correction < 0.2 ppm3.3 M pairs, total width ~1300 ppmJune 8-22, 2004

  • 1H Asymmetry ResultQ2 = 0.099 (GeV/c)2 Araw = -0.95 ppm 0.20 ppm (stat)9.5 M pairs, total width ~620 ppmAraw correction ~ 0.06 ppmJune 24-July 25, 2004

  • Summary of 1H and 4He Results GsE = -0.039 0.041(stat) 0.010(syst) 0.004(FF)

    GsE + 0.08 GsM = 0.032 0.026(stat) 0.007(syst) 0.011(FF)

  • Current Status and ProspectsGEs + (Q2) GMsQ2 [GeV2]Each experiment consistent with Gs=0Some indication of positive GMsG0 data consistent and provocative!Cancellations might play a roleLet us revisit the charge symmetry assumption

  • Charge Symmetry Violation Estimates

  • Strange Quarks or CSV?Need consensus on effects of CSV on GEs:Better quark models?Additional work on chiral perturbation theory?Handles from observed CSB effects in nucleon systems?95% C.L.

  • SummaryCSV in parton distributions at high xParity violating DIS quite sensitiveCould be part rich 11 GeV programCSV in nucleon form factorsParity violating elastic scattering increasingly sensitive: strange quarks or CSV?Can theory help constrain effects in GE?Can existing data on CSV help?Are there new experimental handles on CSV in the context of nucleon form factors?Critical to resolve the issue if strange quark interpretation is to be clean


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