17 October 2006Parity Violating Electron Scattering1 Parity Violating Electron Scattering: Interplay Between Electroweak Physics and Hadronic Physics Weak Interaction Physics from the JLab Point of View Krishna Kumar University of Massachusetts, Amherst Acknowledgement: J. Erler, C. Horowitz, W.J. Marciano, M.J. Ramsey-Musolf, K. Paschke, J. Piekerewicz, M. Pitt, P. Souder October 17, 2006 Physics of Nucleons and Nuclei: SURA Workshop, Washington D.C.

17 October 2006Parity Violating Electron Scattering2 1960s: An Electroweak Model of Leptons (and quarks) –SU(2) L X U(1) Y gauge theory predicted the Z boson –sin 2  W introduced to predict lepton & quark Z couplings 1973: antineutrino-electron scattering –First weak neutral current observation Mid-70s: Does the Weak Neutral Current interfere with the Electromagnetic Current? –Central to establishing SU(2) L X U(1) Y Weak Neutral Current (WNC) Interactions Gargamelle observes one  e - event First measurement of sin 2  W Parity is violated Parity is conserved Consider fixed target electron scattering Low energy WNC interactions (Q 2 <<M Z 2 ) Historical Context: Z0Z0

17 October 2006Parity Violating Electron Scattering3 Parity-Violating Electron Scattering Neutron  Decay Electron-proton Weak Scattering Parity-violating A PV ~ (GeV 2 ) It was realized independently in the mid 70s at SLAC: A PV in Deep Inelastic Scattering off liquid Deuterium: Q 2 ~ 1 (GeV) 2 Ya. Zel’dovich (1959)  E E’ 4-momentum transfer

17 October 2006Parity Violating Electron Scattering4 PV Electron Scattering off a Nucleus Optical pumping of a GaAs wafer Rapid helicity reversal Control of helicity-correlated beam motion “Flux Integration”: Allows counting at high rates Spectrometer directs flux to background-free region Feinberg (1975), Donnelly and Walecka (1975) Elastic scattering: 0 +  0 + Spinless, isoscalar nucleus One form factor; charge monopole: cancels in the asymmetry ratio A PV independent of nuclear structure; nucleus acts as filter: different linear combination of quark couplings accessed For elastic scattering off nucleus: Q 2 << 0.1 GeV 2  A PV ~ 1 ppm MIT-Bates: P. Souder et al (1990) New innovative methods to control systematic effects A stat ~ 10 -7, A syst ~ 10 -8

17 October 2006Parity Violating Electron Scattering5 Spinoff: Nucleon Structure Studies QCD and the Quark Model SU(3) f symmetry-breaking introduces uncertainties Strange mass: 0-20%  N scattering: What about the nucleon’s charge and magnetization distributions? Neutrino deep inelastic scattering Semi-inclusive DIS (HERMES) (Needs fragmentation functions) Polarized target technology & high-luminosity polarized beams made new experiments feasible Fraction of nucleon momentum Parton distribution functions Sea quarks, especially strange quarks, can provide new insight Part per billion systematic control facilitated new experimental program

17 October 2006Parity Violating Electron Scattering6 Elastic Electroweak Scattering G E s (Q 2 ), G M s (Q 2 ) A PV for elastic e-p scattering: Forward angle Backward angle Helium: Unique G E sensitivity Deuterium: Enhanced G A sensitivity Z0Z0 Kaplan & Manohar (1988) McKeown (1989)

17 October 2006Parity Violating Electron Scattering7 Overview of Experiments G M s, (G A ) at Q 2 = 0.1 GeV 2 SAMPLE HAPPEX G E s G M s at Q 2 = 0.48 GeV 2 G E s G M s at Q 2 = 0.1 GeV 2 G E s at Q 2 = 0.1 GeV 2 ( 4 He) open geometry, integrating A4 G E s G M s at Q 2 = 0.23 GeV 2 G E s G M s at Q 2 = 0.1 GeV 2 G M s, G A e at Q 2 = 0.1, 0.23, 0.5 GeV 2 Open geometry Fast counting calorimeter for background rejection G0 G E s +  G M s over Q 2 = [0.12,1.0] GeV 2 G M s, G A e at Q 2 = 0.23, 0.62 GeV 2 Open geometry Fast counting with magnetic spectrometer + TOF for background rejection

17 October 2006Parity Violating Electron Scattering8 New HAPPEX Results (final) Asymmetry (ppm) Slug Hydrogen A raw correction ~11 ppb Slug Asymmetry (ppm) Helium normalization error ~ 2% A PV =  0.12 (stat)  0.04 (syst) ppm A(G s =0) = ppm  0.05 ppm Hydrogen A PV =  0.23 (stat)  0.12 (syst) ppm A(G s =0) = ppm Helium nucl-ex/ , submitted to PRL Fit to world data consistent (R. Young et al, nucl-ex/ ) Result insensitive to axial form factors

17 October 2006Parity Violating Electron Scattering9 Implications and Outlook Forward angle e-p data Approved program well-matched to ultimate sensitivity of the technique: charge symmetry, radiative corrections, axial form factors….. Models dealing with “sea” properties are challenging Experimentally, 20-year old quest nearing completion Ultimate insight: unquenched Lattice QCD calculations with light chiral quarks Rapid variation at low Q 2 unlikely Await backward angle measurements from A4, G0 Deuterium running will provide constraints on G A One high precision point at Q 2 ~0.6 G M s = / G E s = / ~0.2 +/- 0.5% of electric distribution ~3% +/- 2.3% of proton magnetic moment (<20% of isoscalar magnetic moment) HAPPEX-only fit suggests something even smaller: G M s = / G E s = / Technology pushed to new levels: opens new physics topics

17 October 2006Parity Violating Electron Scattering10 Elastic Electroweak Scattering off 208 Pb A technically demanding measurement: Rate ~ 2 GHz Separate excited state ~ 2.5 MeV Stat. Error ~ 15 ppb Syst. Error ~ 1 to 2 %  (A PV ) ~ 3%  (R p -R n ) ~ 1% Q 2 ~ 0.01 GeV 2 A PV ~ 0.5 ppm Tight control of beam properties New “warm” septum High power Lead target New 18-bit ADC New radiation-hard detector Polarimetry upgrade Q p EM ~ 1Q n EM ~ 0 Q p W ~ 1 - 4sin 2  W Q n W ~ 1  All elements in place in 2008 Comments on physics: Bill, Chuck & Jorge Comments on technology: Gordon Donnelly, Dubach and Sick (1989) C. Horowitz, R. Michaels et al (2001)

17 October 2006Parity Violating Electron Scattering11 Beyond the Standard Model Low Energy: Q 2 << M Z 2 New Particle Searches Rare or Forbidden Processes Symmetry Violations Electroweak One-Loop Effects High Energy Colliders as well as Low Q 2 offers complementary probes of physics at high energy scales Neutrino Physics –Oscillations and the MSN matrix –Tritium Beta Decay and Double Beta Decay Muon Physics –g-2 anomaly –Precision muon decay parameters –Charged lepton number violation Semi-leptonic Weak Decays –Standard Model CP Violation –Tests of CKM unitarity –Anomalous charged current interactions –Search for Proton decay Dark Matter Searches Electric Dipole Moment Searches Neutral Weak Interaction Studies

17 October 2006Parity Violating Electron Scattering12 Comprehensive Search for New Neutral Current Interactions Neutral Current Interactions are Flavor Diagonal Any new physics model can be characterized in this way: Heavy Z’s, compositeness, extra dimensions… Relying on specific models to sell a measurement is not good strategy: Models will go in and out of fashion over a 5-10 year span One goal of neutral current measurements at low energy AND colliders: Access  > 10 TeV for as many f 1 f 2 and L,R combinations as possible Consider or Different  ’s for all f 1 f 2 combinations and L,R combinations Eichten, Lane and Peskin, PRL50 (1983)

17 October 2006Parity Violating Electron Scattering13 Colliders vs Low Q 2 LEPII, Tevatron access scales  ’s ~ 10 TeV Window of opportunity for weak neutral current measurements at Q 2 <<M Z 2 e.g. Tevatron dilepton spectra, quark pair production at LEPII - L,R combinations accessed are parity-conserving LEP & SLC accessed some parity-violating combinations but…

17 October 2006Parity Violating Electron Scattering14 Published & Future Measurements Atomic Parity Violation 133 Cs 6s to 7s transition Future: Radioactive beams Neutrino DIS: NuTeV 3  deviation Many hadronic physics issues Parity-Violating electron-electron (Møller) scattering: SLAC E158 Purely leptonic Most precise measurement Running of weak mixing angle Elastic electron-proton scattering Proton is “fundamental” at Q 2 <<0.1GeV 2 (strange quark measurements) Theory and experimental systematics under control Deep-Inelastic scattering off deuterium Jlab 11 GeV enables comprehensive measurements Møller scattering Jlab 11 GeV enables greatly improved figure-of-merit Future

17 October 2006Parity Violating Electron Scattering15 Qweak at JLab A PV in elastic e-p scattering Physics Asymmetry: Region 3: Vertical Drift chambers Region 2: Horizontal drift chamber location Region 1: GEM Gas Electron Multiplier Quartz Cerenkov Bars (insensitive to non-relativistic particles) Collimator System Mini-torus QTOR Magnet Trigger Scintillator Lumi Monitors e - beam  (A PV ) ~ 3%  (sin 2  W ) ~ ± Design under way Data ~ 2010

17 October 2006Parity Violating Electron Scattering16 Lepton-Quark WNC Couplings NuTeV motivates closer look at lepton-quark WNC couplings 4 model-independent e-q couplings to nail down Implications for models of new TeV scale physics 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 ~ 10 GeV beam Possible after 12 GeV upgrade of Jefferson Lab ( )

17 October 2006Parity Violating Electron Scattering17 PV DIS at 11 GeV with an LD 2 target Important constraint for Large Hadron Collider anomalies However, extraction of C 2i ’s assumes nucleon with valence quarks Need to characterize nucleon structure at high-x to high precision This is one of the core missions of the 11 GeV Jlab program! e-e- N X e-e- Z*Z* ** For an isoscalar target like 2 H, structure functions largely cancel in the ratio: (Q 2 >> 1 GeV 2, W 2 >> 4 GeV 2, x ~ ) Must measure A PV to 0.5% fractional accuracy! Luminosity and beam quality available at JLab

17 October 2006Parity Violating Electron Scattering18 1% A PV measurements Precision High-x Physics with PV DIS Charge Symmetry Violation (CSV) at High x: clean observation possible? Allows d/u measurement on a single proton! Vector quark current! (electron is axial-vector) Longstanding issue: d/u as x  1 For hydrogen 1 H: Blue curve: Gluck, Jimenez-Delgado, Reya +Thomas and Londergan

17 October 2006Parity Violating Electron Scattering19 A Vision for Precision PV DIS Physics 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 –(Except x~0.75) 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 Need BaBar, CDF or CLEOII Solenoid roughly 10-15M$ project Plan to make presentations at Symmetries and Hadrons Town Meetings

17 October 2006Parity Violating Electron Scattering20 The Average: sin 2 θ w = (17) Weak Mixing Angle at HIGH Energy A LR A FB (Z→ bb) sin 2 θ w = (3) ↓ m H = GeV S= ± 17 sin 2 θ w = (3) ↓ m H = GeV S= ± 17 Rules out the SM! Rules out SUSY! Favors Technicolor! Rules out Technicolor! Favors SUSY! (also APV in Cs) (also E158) 3σ apart Tevatron & LHC will make some improvements on M W sin 2  W improvements at hadron colliders very challenging Must wait for “Giga-Z” option of ILC or Neutrino Factory Jlab e2e coule be the best measurement until 2020 W. Marciano, CIPANP06, EW & BSM Session JLab 12 GeV

17 October 2006Parity Violating Electron Scattering21 Summary New HAPPEX results on nucleon neutral weak form factors: Helium: G s E =  (stat)  (syst) (Q 2 = GeV 2 ) Hydrogen: G s E +0.09G s M =  (stat)  (syst)  (FF) Final measurements to be completed within two years A clean measurement of the neutron distribution in 208 Pb: implications for nuclear structure & neutron star properties Precision sin 2  W at low energy constrain TeV scale physics Running of weak mixing angle established at 6  Qweak will provide complementary information Møller JLab 12 GeV competes with colliders New era of PV DIS measurements with JLab 12 GeV upgrade We prepare to make a pitch during Long Range Planning