18 June 2005PVES & CSB 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 In collaboration with: Kent Paschke (UMass) Paul Souder (Syracuse) Robert Michaels (Jlab)

18 June 2005PVES & CSB 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

18 June 2005PVES & CSB PV Asymmetries to For electrons scattering off nuclei or nucleons: Z couplings provide access to different linear combination of underlying quark substructure (g e g T )

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

18 June 2005PVES & CSB Electroweak Physics at Low Q 2 LEPII, Tevatron, LHC access scales greater than  ~ 10 TeV Logical to push to higher energies, away from the Z resonance Parity Conserving Contact Interactions Parity Violating Contact Interactions Q 2 << scale of EW symmetry breaking

18 June 2005PVES & CSB Weak Neutral Current at low Q 2 Purely leptonic reaction Q e W ~ 1 - 4sin 2  W Z0Z0 Fixed Target Møller Scattering E158 at Stanford Linear Accelerator Center Institutions CaltechSyracuse PrincetonJefferson Lab SLACUC Berkeley CEA SaclayUMass Amherst Smith CollegeU. of Virginia 60 physicists, 7 Ph.D. students

18 June 2005PVES & CSB 3% sin 2  eff = ± ± Czarnecki and Marciano Erler and Ramsey-Musolf Sirlin et. al. Zykonov SLAC E158 Final Result 66 sin 2  W MS (M Z ) hep-ex/ , To be published in PRL * Limit on  LL ~ 7 or 16 TeV * Limit on SO(10) Z’ ~ 1.0 TeV * Limit on lepton flavor violating coupling ~ 0.01G F (95% confidence level)

18 June 2005PVES & CSB Future Possibilities (Leptonic) -e in reactor SLAC E158 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 can test neutrino coupling: sin 2  W to ± Møller at 11 GeV at Jlab sin 2  W to ± !  ee ~ 25 TeV reach! Higher luminosity and acceptance Longstanding discrepancy between hadronic and leptonic Z asymmetries: Z pole asymmetries

18 June 2005PVES & CSB Future Possiblities (Semileptonic) Qweak at Jlab measure sin 2  W to ± nail down fundamental low energy lepton-quark WNC couplings NuTeV A V V A C 2i ’s small & poorly known: difficult to measure in elastic scattering PV Deep inelastic scattering experiment with high luminosity 11 GeV beam A PV in elastic e-p scattering (2008)

18 June 2005PVES & CSB Lepton Deep Inelastic Scattering b ~ 0.2 fm/sqrt(t) t=(p-p‘) 2 r ~ 0.2 fm/Q (0.02 – 0.2 fm for 100>Q 2 >1 GeV 2 ) transverse size of probe ** ct b ct ~ 0.2 fm (1/2x) (<1 fm to 1000‘s fm) – scale over which photon fluctuations survive. For x~1: valence quark structure Fraction of proton momentum carried by struck quark r Cross-sections fall steeply with (1-x) n Need high luminosity at high energy Jefferson Lab upgraded to 11 GeV, 90 µA CW beam Courtesey A. Caldwell Parton distribution functions f i (x) poorly measured at high x Lacking some fundamental knowledge of proton structure

18 June 2005PVES & CSB Parity Violating Electron DIS f i (x) are quark distribution functions e-e- N X e-e- Z*Z* ** For an isoscalar target like 2 H, structure functions largely cancel in the ratio: Provided Q 2 >> 1 GeV 2 and W 2 >> 4 GeV 2 and x ~ Must measure A PV 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

18 June 2005PVES & CSB 2 H Experiment at 11 GeV E’: 5.0 GeV ± 10%  lab = 12.5 o A PV = 217 ppm I beam = 90 µA 60 cm LD 2 target Use both HMS and SHMS to increase solid angle ~2 MHz DIS rate, π/e ~ 2-3 x Bj ~ 0.235, Q 2 ~ 2.6 GeV 2, W 2 ~ 9.5 GeV hours  (A PV )=0.65 ppm  (2C 2u -C 2d )=±0.0086± PDG (2004): ± 0.24 Theory: Advantages over 6 GeV: Higher Q 2, W 2, f(y) Lower rate, better π/e Better systematics: 0.7%

18 June 2005PVES & CSB Physics Implications Examples: 1 TeV extra gauge bosons (model dependent) TeV scale leptoquarks with specific chiral couplings Unique, unmatched constraints on axial-vector quark couplings: Complementary to LHC direct searches  (2C 2u -C 2d )=0.012  (sin 2  W )=0.0009

18 June 2005PVES & CSB 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

18 June 2005PVES & CSB Search for CSV in PV DIS Sensitivity will be further enhanced if u+d falls off more rapidly than  u-  d as x  1 measure or constrain higher twist effects at x ~ precision measurement of A PV at x ~ 0.7 to search for CSV Strategy: 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 For A PV in electron- 2 H DIS:

18 June 2005PVES & CSB Potential Sensitivity

18 June 2005PVES & CSB )( 3 2 )( 3 1 )( 3 1 )( 18 1 )( 2 1     SS SSS uud d udu u up d(x)/u(x) as x  1 Proton Wavefunction (Spin and Flavor Symmetric) SU(6): d/u~1/2 Valence Quark: d/u~0 Perturbative QCD:d/u~1/5 Allows d/u measurement on a single proton! Vector quark current! (electron is axial-vector) PV-DIS off hydrogen Longstanding issue in proton structure

18 June 2005PVES & CSB A New A PV DIS Program 2 to 3.5 GeV scattered electrons 20 to 40 degrees Factor of 2 in Q 2 range High statistics at x=0.7, with W>2

18 June 2005PVES & CSB A PV DIS Program with upgraded JLab Hydrogen and Deuterium targets Better than 2% errors –It is unlikely that any effects are larger than 10% x-range W 2 well over 4 GeV 2 Q 2 range a factor of 2 for each x point –(Except x~0.7) Moderate running times CW 90 µA at 11 GeV 40 cm liquid H 2 and D 2 targets Luminosity > /cm 2 /s solid angle > 200 msr Count at 100 kHz online pion rejection of 10 2 to 10 3

18 June 2005PVES & CSB Dynamics of Low Energy QCD (  0.2 fm) Profound qualitative and quantitative implications!

18 June 2005PVES & CSB Strangeness in Nucleons ? Breaking of SU(3) flavor symmetry introduces uncertainties Kaplan & Manohar (1988) McKeown (1990) G E s (Q 2 ), G M s (Q 2 )

18 June 2005PVES & CSB Parity Violating Amplitude dominated by NC terms: NC vector current probes same hadronic flavor structure, with different couplings: Electron Elastic Electroweak Scattering

18 June 2005PVES & CSB commonly used Sachs FF: Decompose by Quark Flavor: Flavor Decomposed Form Factors

18 June 2005PVES & CSB Charge symmetry: u-quark distribution in the proton is the same as the d-quark distribution in the neutron G  p E,M G s E,M G u E,M G d E,M G  n E,M Isospin symmetry G  p E,M G n E,M G p E,M G s E,M Pick ‘n Choose Well Measured Charge Symmetry

18 June 2005PVES & CSB How Big? Various theoretical approaches: Quark models Dispersion Relations Lattice Gauge theory Skyrme models ? Hammer Ramsey-Musolf Dispersion Theory

18 June 2005PVES & CSB Elastic Electroweak Measurements A PV measurements ranging 0.1 < Q 2 < 1 forward and backward angles Hydrogen, Deuterium and Helium targets Statistical and systematic errors < 10% Rough guide: G E n (Q 2 =0.2) ~ 0.05,   ~ -0.6 SAMPLE GMsGMs G A (T=1) G E s +  (Q 2 ) G M s Q 2 (GeV/c) 2 Cancellations? Q 2 dependence? Accuracy? HAPPEX: Second Generation E=3 GeV,  =6 deg, Q 2 =0.1 (GeV/c) 2 1 H: A PV =-1.4 ppm, goal ± 0.08 (stat.)  (G s E +0.08G s M ) =  (G s E ) = He: A PV =+7.6 ppm, goal ± 0.18 (stat.)

18 June 2005PVES & CSB HAPPEX at JLab 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 Hall A Proton Parity EXperiment : Q 2 =0.5 GeV 2, 1 H : Q 2 =0.1 GeV 2, 1 H, 4 He

18 June 2005PVES & CSB Spectrometers & Detectors Beam diagnostics Quadrupole magnets Bending magnet Target Septum magnets Compton polarimeter Cherenkov cones PMT 12 m dispersion sweeps away inelastic events

18 June 2005PVES & CSB 4 He Asymmetry Result Q 2 = (GeV/c) 2 A raw = 5.63 ppm  0.71 ppm (stat) A raw correction < 0.2 ppm Helicity Window Pair Asymmetry 3.3 M pairs, total width ~1300 ppm June 8-22, 2004 A PV = 6.72  0.84 (stat)  0.21 (syst) ppm Submitted to PRL: nucl/ex Data: (after all corrections) A(G s =0) =  0.08 ppm Theory

18 June 2005PVES & CSB 1 H Asymmetry Result Q 2 = (GeV/c) 2 A raw = ppm  0.20 ppm (stat) Helicity Window Pair Asymmetry 9.5 M pairs, total width ~620 ppm A raw correction ~ 0.06 ppm June 24-July 25, 2004 A PV =  0.24 (stat)  0.06 (stat) ppm Submitted to PRL: nucl/ex Data: (after all corrections) A(G s =0) = ppm  0.11 ppm Theory

18 June 2005PVES & CSB (S.L.Zhu et. al.) Summary of 1 H and 4 He Results G s E =  (stat)  (syst)  (FF) G s E G s M =  (stat)  (syst)  (FF)

18 June 2005PVES & CSB G E s +  (Q 2 ) G M s Q 2 [GeV 2 ] Current Status and Prospects Each experiment consistent with G s =0 Some indication of positive G M s G0 data consistent and provocative! Cancellations might play a role Let us revisit the charge symmetry assumption

18 June 2005PVES & CSB Charge Symmetry Violation Estimates Simple estimate on G M s C. Horowitz leads to different magnetic moments Assume m u different from m d is only source Propagates to n.m. Non-relativistic constituent quark models G. Miller Account for mass difference, Coulomb and hyperfine interaction G M s effects less than 1% over relevant range of Q 2 G E s effects between 1 and 2% at Q 2 ~ 0.1 GeV 2 Are relativistic effects important? Pion cloud effects small and calculable Chiral Perturbation Theory Lewis and Mobed G M s effects similar Unknown normalization at Q 2 =0? G E s estimated at LO: NLO not parameter-free Can one carry isospin violation effects in G E to NLO?

18 June 2005PVES & CSB Strange Quarks or CSV? Need consensus on effects of CSV on G E s : Better quark models? Additional work on chiral perturbation theory? Handles from observed CSB effects in nucleon systems? 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? 95% C.L.

18 June 2005PVES & CSB 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 G E ? –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