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Parity-Violating Electron Scattering & Charge Symmetry Breaking

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.

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Parity-Violating Electron Scattering & Charge Symmetry Breaking

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  1. 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 Kent Paschke (UMass) Paul Souder (Syracuse) Robert Michaels (Jlab) In collaboration with: PVES & CSB

  2. Outline • Parity-Violating Electron Scattering • Deep Inelastic Scattering • Physics with 11 GeV Electrons • Beyond the Standard Model • Search for Charge Symmetry Violation • d/u • Towards a 11 GeV Program • Elastic Electron-Nucleon Scattering • Strangeness in Nucleons • Recent Results • Charge Symmetry Assumption • Outlook PVES & CSB

  3. PV Asymmetries to (gegT) For electrons scattering off nuclei or nucleons: Z couplings provide access to different linear combination of underlying quark substructure PVES & CSB

  4. 2005: MeV to TeV Physics 1970s 1980s • Steady progress in technology • part per billion systematic control • 1% normalization control 1990s Recent Results Result Today! Future Three different avenues of investigation: TeV Physics • 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 Physics MeV Physics • Valence quark structure of the nucleon: Jlab at 12 GeV PVES & CSB

  5. Electroweak Physics at Low Q2 Q2 << scale of EW symmetry breaking Parity Violating Contact Interactions Logical to push to higher energies, away from the Z resonance LEPII, Tevatron, LHC access scales greater than L ~ 10 TeV Parity Conserving Contact Interactions PVES & CSB

  6. E158 at Stanford Linear Accelerator Center Caltech Syracuse Princeton Jefferson Lab SLAC UC Berkeley CEA Saclay UMass Amherst Smith College U. of Virginia Institutions 60 physicists, 7 Ph.D. students Weak Neutral Current at low Q2 Fixed Target Møller Scattering Purely leptonic reaction QeW ~ 1 - 4sin2W Z0 PVES & CSB

  7. sin2eff = 0.2397 ± 0.0010 ± 0.0008 sin2WMS(MZ) Czarnecki and Marciano Erler and Ramsey-Musolf Sirlin et. al. Zykonov 3% 6s (95% confidence level) * Limit on LLL ~ 7 or 16 TeV * Limit on SO(10) Z’ ~ 1.0 TeV • * Limit on lepton flavor violating coupling ~ 0.01GF SLAC E158 Final Result hep-ex/0504049, To be published in PRL PVES & CSB

  8. Møller at 11 GeV at Jlab sin2W to ± 0.00025! ee ~ 25 TeV reach! Higher luminosity and acceptance Longstanding discrepancy between hadronic and leptonic Z asymmetries: Z pole asymmetries Kurylov, Ramsey-Musolf, Su 95% C.L. JLab 12 GeV Møller Does Supersymmetry (SUSY) provide a candidate for dark matter? • Neutralino is stable if baryon (B) and lepton (L) numbers are conserved • B and L need not be conserved (RPV): neutralino decay Future Possibilities (Leptonic) -e in reactor can test neutrino coupling: sin2W to ± 0.002 SLAC E158 PVES & CSB

  9. (2008) Future Possiblities (Semileptonic) NuTeV Qweak at Jlab APV in elastic e-p scattering • measure sin2W to ± 0.0007 • nail down fundamental low energy lepton-quark WNC couplings A V V A • C2i’s small & poorly known: difficult to measure in elastic scattering • PV Deep inelastic scattering experiment with high luminosity 11 GeV beam PVES & CSB

  10. ct r * Fraction of proton momentum carried by struck quark ct ~ 0.2 fm (1/2x) (<1 fm to 1000‘s fm) – scale over which photon fluctuations survive. For x~1: valence quark structure Parton distribution functions fi(x) poorly measured at high x Lacking some fundamental knowledge of proton structure Cross-sections fall steeply with (1-x)n Need high luminosity at high energy Jefferson Lab upgraded to 11 GeV, 90 µA CW beam Lepton Deep Inelastic Scattering r~ 0.2 fm/Q (0.02 – 0.2 fm for 100>Q2>1 GeV2) transverse size of probe b Courtesey A. Caldwell b~ 0.2 fm/sqrt(t) t=(p-p‘)2 PVES & CSB

  11. Parity Violating Electron DIS e- e- * Z* X N fi(x) are quark distribution functions 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 - 0.4 Must 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 PVES & CSB

  12. 1000 hours (APV)=0.65 ppm (2C2u-C2d)=±0.0086±0.0080 PDG (2004): -0.08 ± 0.24 Theory: +0.0986 2H Experiment at 11 GeV E’: 5.0 GeV ± 10% lab = 12.5o 60 cm LD2 target Ibeam = 90 µA • Use both HMS and SHMS to increase solid angle • ~2 MHz DIS rate, π/e ~ 2-3 APV = 217 ppm xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2 • Advantages over 6 GeV: • Higher Q2, W2, f(y) • Lower rate, better π/e • Better systematics: 0.7% PVES & CSB

  13. (2C2u-C2d)=0.012 (sin2W)=0.0009 Unique, unmatched constraints on axial-vector quark couplings: Complementary to LHC direct searches • 1 TeV extra gauge bosons (model dependent) • TeV scale leptoquarks with specific chiral couplings Examples: Physics Implications PVES & CSB

  14. PV DIS and Nucleon Structure • Analysis assumed control of QCD uncertainties • Higher twist effects • Charge Symmetry Violation (CSV) • d/u at high x • NuTeV provides perspective • Result is 3 from theory prediction • Generated a lively theoretical debate • Raised very interesting nucleon structure issues: cannot be addressed by NuTeV • JLab at 11 GeV offers new opportunities • PV DIS can address issues directly • Luminosity and kinematic coverage • Outstanding opportunities for new discoveries • Provide confidence in electroweak measurement PVES & CSB

  15. For APV in electron-2H DIS: Strategy: • measure or constrain higher twist effects at x ~ 0.5-0.6 • precision measurement of APV at x ~ 0.7 to search for CSV Search for CSV in PV DIS • u-d mass difference • electromagnetic effects • Direct observation of parton-level CSV would be very interesting • Important implications for high energy collider pdfs • Could explain significant portion of the NuTeV anomaly Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x  1 PVES & CSB

  16. Potential Sensitivity PVES & CSB

  17. 1 1 1 ­ = ­ + ­ - ¯ p u ( ud ) u ( ud ) u ( ud ) = = = 0 1 1 S S S 3 2 18 1 2 - ­ - ¯ d ( uu ) d ( uu ) Perturbative QCD: d/u~1/5 = = S 1 S 1 3 3 SU(6): Valence Quark: d/u~0 d/u~1/2 Longstanding issue in proton structure PV-DIS off hydrogen • Allows d/u measurement on a single proton! • Vector quark current! (electron is axial-vector) d(x)/u(x) as x1 Proton Wavefunction (Spin and Flavor Symmetric) PVES & CSB

  18. A New APV DIS Program • 2 to 3.5 GeV scattered electrons • 20 to 40 degrees • Factor of 2 in Q2 range • High statistics at x=0.7, with W>2 PVES & CSB

  19. solid angle > 200 msr • Count at 100 kHz • online pion rejection of 102 to 103 A PV DIS Program with upgraded JLab • CW 90 µA at 11 GeV • 40 cm liquid H2 and D2 targets • Luminosity > 1038/cm2/s • Hydrogen and Deuterium targets • Better than 2% errors • It is unlikely that any effects are larger than 10% • x-range 0.25-0.75 • W2 well over 4 GeV2 • Q2 range a factor of 2 for each x point • (Except x~0.7) • Moderate running times PVES & CSB

  20. Dynamics of Low Energy QCD ( 0.2 fm) Profound qualitative and quantitative implications! PVES & CSB

  21. Kaplan & Manohar (1988) McKeown (1990) GEs(Q2), GMs(Q2) Strangeness in Nucleons Breaking of SU(3) flavor symmetry introduces uncertainties ? PVES & CSB

  22. Electron Elastic Electroweak Scattering Parity Violating Amplitude dominated by NC terms: NC vector current probes same hadronic flavor structure, with different couplings: PVES & CSB

  23. Flavor Decomposed Form Factors commonly used Sachs FF: Decompose by Quark Flavor: PVES & CSB

  24. Gg,pE,M GuE,M GpE,M Isospinsymmetry Gg,nE,M GdE,M Pick ‘n Choose GnE,M GsE,M GZ,pE,M GsE,M Well Measured <N| sgm s |N> Charge Symmetry Charge symmetry: u-quark distribution in the proton is the same as the d-quark distribution in the neutron PVES & CSB

  25. Dispersion Theory ? Hammer Ramsey-Musolf • Quark models • Dispersion Relations • Lattice Gauge theory • Skyrme models Various theoretical approaches: How Big? PVES & CSB

  26. GEs + a(Q2) GMs SAMPLE Q2 (GeV/c)2 GMs E=3 GeV, q=6 deg, Q2=0.1 (GeV/c)2 HAPPEX: Second Generation 4He: APV=+7.6 ppm, goal ± 0.18 (stat.) 1H: APV=-1.4 ppm, goal ± 0.08 (stat.) GA(T=1)  (GsE ) = 0.014  (GsE+0.08GsM ) = 0.010 Elastic Electroweak Measurements • APV measurements ranging 0.1 < Q2 < 1 • forward and backward angles • Hydrogen, Deuterium and Helium targets • Statistical and systematic errors < 10% Rough guide: GEn(Q2=0.2) ~ 0.05,  ~ -0.6 • Cancellations? • Q2 dependence? • Accuracy? PVES & CSB

  27. HAPPEX at JLab Hall A Proton Parity EXperiment 1998-99: Q2=0.5 GeV2, 1H 2004-05: Q2=0.1 GeV2, 1H, 4He The 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 Mary PVES & CSB

  28. Cherenkov cones 12 m dispersion sweeps away inelastic events PMT Spectrometers & Detectors Compton polarimeter Target Beam diagnostics Bending magnet Septum magnets Quadrupole magnets PVES & CSB

  29. Helicity Window Pair Asymmetry Theory A(Gs=0) = +7.51  0.08 ppm Data: (after all corrections) APV = 6.720.84(stat)0.21(syst) ppm Submitted to PRL: nucl/ex-0506010 4He Asymmetry Result June 8-22, 2004 3.3 M pairs, total width ~1300 ppm Araw correction < 0.2 ppm Q2 = 0.091 (GeV/c)2 Araw = 5.63 ppm 0.71 ppm (stat) PVES & CSB

  30. Helicity Window Pair Asymmetry Theory A(Gs=0) = -1.44 ppm 0.11 ppm Data: (after all corrections) APV = -1.140.24(stat)0.06(stat)ppm Submitted to PRL: nucl/ex-0506011 1H Asymmetry Result June 24-July 25, 2004 9.5 M pairs, total width ~620 ppm Araw correction ~ 0.06 ppm Q2 = 0.099 (GeV/c)2 Araw = -0.95 ppm 0.20 ppm (stat) PVES & CSB

  31. (S.L.Zhu et. al.) 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) PVES & CSB

  32. Current Status and Prospects GEs + (Q2) GMs Q2 [GeV2] • Each experiment consistent with Gs=0 • Some indication of positive GMs • G0 data consistent and provocative! • Cancellations might play a role Let us revisit the charge symmetry assumption PVES & CSB

  33. Assume mu different from md is only source Simple estimate on GMs C. Horowitz leads to different magnetic moments Propagates to 0.007 n.m. Non-relativistic constituent quark models G. Miller Account for mass difference, Coulomb and hyperfine interaction GMs effects less than 1% over relevant range of Q2 GEs effects between 1 and 2% at Q2 ~ 0.1 GeV2 Are relativistic effects important? GMs effects similar Chiral Perturbation Theory Lewis and Mobed Unknown normalization at Q2=0? Pion cloud effects small and calculable GEs estimated at LO: NLO not parameter-free Can one carry isospin violation effects in GE to NLO? Charge Symmetry Violation Estimates PVES & CSB

  34. We would like to be able to claim non-trivial dynamics of the sea in the static properties of the nucleon: is that viable? Any other experimental CSV handles? Strange Quarks or CSV? 95% C.L. 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? PVES & CSB

  35. Summary • CSV in parton distributions at high x • Parity violating DIS quite sensitive • Could be part rich 11 GeV program • CSV in nucleon form factors • Parity 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 PVES & CSB

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