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Conclusions and Perspectives

Conclusions and Perspectives. Krishna Kumar UMass Amherst PAVI06 20 May 2006. ΜΗΛΟΣ. Acknowledgements. Pictures, thoughts and ideas from: B. Holstein, K. Paschke, M.J. Ramsey-Musolf, P. Souder, M. Vanderhaeghen and all the speakers. Many thanks for the invitation:

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Conclusions and Perspectives

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  1. Conclusions and Perspectives Krishna Kumar UMass Amherst PAVI06 20 May 2006 ΜΗΛΟΣ Conclusions & Perspectives

  2. Acknowledgements Pictures, thoughts and ideas from: B. Holstein, K. Paschke, M.J. Ramsey-Musolf, P. Souder, M. Vanderhaeghen and all the speakers • Many thanks for the invitation: • K. De Jager, S. Kox, D. Lhuillier, F. Maas, S. Page, C. Papanicolas, S. Stiliaris • Ideal workshop setting: • Great location, organization and staff • Excellent Scientific Program: • Many exciting and interconnected subfields Conclusions & Perspectives

  3. Come On! Disclaimer I am a dumb experimentalist: The following is a personal view of the status of the field and its immediate future. I apologize in advance for any omissions • Many thanks for the invitation: • Thanks for a sleepless week! • Ideal workshop setting: • How are you supposed to get anything done?! • Didn’t you know this island has good ouzo?! • Excellent Scientific Program: • Hey, I did’nt know it was going to be this broad when I accepted! You tricked me!!! • But I learned a lot…. Conclusions & Perspectives

  4. Neutral Weak Interactions • The 50’s • Yang-Mills Theory • Zel’dovich and parity violation • The 60’s • Weinberg and SU(2)L X U(1)Y Theory: the Z boson • The 70’s • Neutrino electron scattering • Prescott and Weak Electromagnetic Interference • The 80’s • Observation of W and Z bosons • Atomic Parity Violation • High statistics parity violating electron scattering • Beginning of the LEP/SLC era: Z factories Low Energy WNC Interactions address a whole range of physics topics: since the 90s, it has become a precision tool Conclusions & Perspectives

  5. WNC Interconnections Electroweak Physics Valence Quark Physics Atomic Physics Nuclear Physics Nucleon Physics Conclusions & Perspectives

  6. The Beginnings Parity is violated Parity is conserved • Gargamelle: neutrino scattering • First weak neutral current observation • Became centerpiece of electroweak theory • SLAC E122: Parity-violating Electron Scattering • Central to establishing SU(2)LXU(1)Y • Established the experimental technique Gargamelle found one e- event in 1973! (two more by 1976) 10 billion events! Conclusions & Perspectives

  7. Weak Neutral Currents and the Atom Conclusions & Perspectives

  8. Atomic Parity Violation Boulder Experiment Power build-up cavity ( F=100 000 ) E Bp B xp xex polarizes the atoms |F,m=±F> Reexcitation of the depleted HF levell Ecole Normale Supérieure, Paris dye laser beam diode laser, tuned to the depleted HF level Ifluo Derevianko, Lintz, Gwinner, Chardonnet, Budker, Sanguinetti, Tsigutkin depletes one HF level APV signal: odd in E, xex, B, Bp, xp Tremendous interest in weak charge, anapole moment and EDM measurements in the larger physics community Conclusions & Perspectives

  9. Atomic Parity Violation Photo-multiplier tubes Oven Collimator Light guide Ytterbium atoms PBC mirror Parabolic 408-nm light y reflector ε Electric field plates 649-nm light x E Magnetic field coils B z Budker, Tsigutkin Electric and magnetic fields define handedness Berkeley Yb Apparatus Anapole Moment • We also heard from: • A. Derevianko with a nice theoretical overview • C. Chardonnet with an update on the search for parity violation in molecules • G. Gwinner with an update on Francium APV and anapole moment measurement preparations • S. Sanguinetti on the TRAP-RAD experiment to trap Francium • Two comments: • It would be interesting to see another nonzero anapole moment, though connections to N-N interaction seem challenging • Is it worth doing the isotope measurements to access the neutron radius by assuming the Standard Model? There is tremendous interest in obtaining more information. Conclusions & Perspectives

  10. Weak Neutral Currents and the Nucleus Conclusions & Perspectives

  11. Hadronic PV EFT Ramsey-Musolf, Holstein, Schiavella, Desplanques, Hyun Done LANSCE, SNS HARD* NIST,SNS Pionless th’y: 5 exp’ts Dynamical pions: 7 exp’ts Medium Range Long Range Short Range Ab initio few-body calculation required Conclusions & Perspectives

  12. Hadronic PV Experiments Transverse Polarization Medium with Parity Violation φ Helicity Components Optical Rotation Bowman, Snow N-4He Spin Rotation Experiment y z We also heard about the npd at LANSCE New versions of these experiments will be launched at the Spallation Neutrion Source Theoretical developments and the SNS have allowed these experiments to gather new momentum Conclusions & Perspectives

  13. Probing Neutron-Rich Matter Constrain neutron halo for APV Constrain neutron star crust thickness Piekerewicz, Michaels QpEM ~ 1 QnEM ~ 0 QnW ~ 1 QpW ~ 1 - 4sin2W  Conclusions & Perspectives

  14. PREx at Jefferson Lab 208 Pb A technically demanding measurement: • Rate ~ 2 GHz • Separate excited state at 2.6 MeV • Stat. Error ~ 15 ppb • Syst. Error ~ 1 to 2 % 12 beam Data collection at JLab Hall A likely in 2008 C Diamond Backing: • High Thermal Conductivity • Negligible Systematics Piekerewicz, Michaels APV ~ 0.5 ppm (APV) ~ 3% (Rp-Rn) ~ 1% Q2 ~ 0.01 GeV2 • Tight control of beam properties • New “warm” septum • New 18-bit ADC • New radiation-hard detector • Polarimetry upgrade Conclusions & Perspectives

  15. Weak Neutral Currents and the Nucleon Conclusions & Perspectives

  16. Nucleon Structure & Strangeness Strange quarks are relatively light What can we say about its role? Breaking of SU(3) flavor symmetry introduces uncertainties pN scattering: Strange mass: 0-20% • Semi-inclusive: Ds = 0.03± 0.03 • fragmentation function Schaefer, Leader, Procureur QCD is intractable at low Q2; what is its relationship to hadron structure? Why don’t sea quarks destroy Quark Model predictions? Neutrino deep inelastic scattering Conclusions & Perspectives

  17. Elastic Electroweak Scattering ~ few parts per million proton: Backward angle Forward angle Kaplan & Manohar (1988) McKeown (1990) GEs(Q2), GMs(Q2) Armstrong, Real, Baunack, Kox, Glaeser, Moffit Helium: Unique GE sensitivity Deuterium: Enhanced GA sensitivity Conclusions & Perspectives

  18. Overview of Experiments Armstrong, Real, Baunack, Kox, Glaeser, Moffit A4 SAMPLE Open geometry Fast counting calorimeter for background rejection open geometry, integrating GEs + 0.23 GMs at Q2 = 0.23 GeV2 GEs + 0.10 GMs at Q2 = 0.1 GeV2 GMs, GAe at Q2 = 0.1, 0.23, 0.5 GeV2 GMs, (GA) at Q2 = 0.1 GeV2 HAPPEX GEs + 0.39 GMs at Q2 = 0.48 GeV2 GEs + 0.08 GMs at Q2 = 0.1 GeV2 GEs at Q2 = 0.1 GeV2 (4He) G0 Open geometry Fast counting with magnetic spectrometer + TOF for background rejection GEs + hGMs over Q2 = [0.12,1.0] GeV2 GMs, GAe at Q2 = 0.23, 0.62 GeV2 Conclusions & Perspectives

  19. Current Status Over the past two years: New data from A4, G0 and HAPPEX Q2 ~ 0.1 GeV2 • Forward angle data nearly finished • One high precision point at Q2~0.6 • Await backward angle measurements from A4, G0 • Deuterium running will provide constraints on GA Conclusions & Perspectives

  20. Strangeness Theory Strangeness in the nucleon has challenged model builders for two decades • Quark Model (Riska) • While the ss-bar component is very compact, specific 5 quark states (with s-bar in the ground state) leads to positive GMs • Chiral Quark Soliton Model (Goeke) • Interesting Q2 dependence will be tested soon! • Heavy Quark Contribution (Toublan) • Raises the issue of the sign of the disconnected light and heavy quark loops • VMD Approach (Bijker, Dubnicka) • Some sensitivity to the assumed asymptotic behaviour of the strange form factors • Lattice Gauge Theoretic Approach (Zanotti, Young) • Nice way to access sea quark dynamics, but a critical component involves a hadronic model without consensus on the assigned error Conclusions & Perspectives

  21. Axial Form Factor Bodek, Schindler • Neutrino oscillations experiments need accurate cross-sections • Discrepancy between neutrino and electroproduction data understood • PV experiments need Q2 dependence for backward angle measurements Minerva will make accurate measurements Conclusions & Perspectives

  22. Charge Symmetry Breaking Lewis Chiral perturbation theory with resonance saturation Conclusions & Perspectives

  23. Nucleon EM Form Factors Alarcon, Pacetti, Dubnicka BLAST at MIT-Bates Low Q2 data critical to reduce systematic error in extraction of Gs Conclusions & Perspectives

  24. Personal Outlook • Forward Angle • Fast variation in the range 0<Q2<0.3 GeV2 ruled out by latest HAPPEX data • Still a window to see non-zero strangeness at Q2~0.6 GeV2 • Charge symmetry, radiative corrections and EM form factor uncertainties preclude any further precision at any Q2 • Backward Angle • New G0 and A4 data sensitive to cancellations at intermediate Q2 • Knowledge of GA and background asymmetries will limit further precision than already proposed • Theory • Models are challenged in dealing with properties purely of the sea • Ultimate insight must come from unquenched lattice calculations with light chiral quarks • Where are we? • We have answered a 20 year-old question about nucleon structure: do strange quark contribute to the charge and magnetization distributions of nucleons? The answer seems to be: smaller than expected but we have to complete the approved program. Beyond that, it is in the realm of lattice QCD. Conclusions & Perspectives

  25. Beam-Normal Asymmetries ' ' Vanderhaeghen, Pasquini, Kaufman, Capozza beam : • Imaginary part of two-photon exchange amplitude • “background” for parity-violation experiments A4 Preliminary at 300 MeV Conclusions & Perspectives

  26. Beam-Normal Asymmetries at JLab Kaufman, Vanderhaeghen First measurement on a nucleus HAPPEX Hydrogen target HAPPEX 11 GeV beam at different Q2 values Conclusions & Perspectives

  27. Gluon Polarization  or  lepton beam proton beam heavy flavor, high pT  or  0, (PHENIX), jets (STAR)  or  STAR proton beam nucleon target  or  Leader, Proceureur • Strangeness and gluon polarization are the only two “purely sea” experimentally accessible observables • RHIC and lepton DIS experiments both agree G is small • They will make inroads, but the ultimate measurements will require a lepton-ion collider: obtain G directly and by DGLAP evolution of g1 Conclusions & Perspectives

  28. Weak Neutral Currents and the Valence Quark Conclusions & Perspectives

  29. NuTeV Anomaly Londergan 3σ below SM agree with SM After ~ three years, no consensus yet No “good” new physics scenario • Assumptions: • Isoscalar target (N=Z) • include only light (u, d) quarks • neglect heavy quark masses • assume isospin symmetry for PDFs • no nuclear effects (parton shadowing, EMC, ….) • no contributions outside Standard Model Community Prejudice: some combination of isospin violation, nuclear effects, strangeness asymmetry and systematics on radiative corrections Conclusions & Perspectives

  30. PV DIS Reimer, Souder, Zheng Address outstanding issues in high x physics • Charge Symmetry Violation • Partonic level CSV has never been observed • Needs high precision with inclusive scattering • d(x)/u(x) at as x  1 • Longstanding QCD prediction • Needs high precision without nuclear effects • Higher Twist • Absence of significant higher twist a surprise • Needs high precision on “predictable” reaction Conclusions & Perspectives

  31. PV DIS with JLab Upgrade For hydrogen 1H: 1% APV measurements Longstanding issue: d/u as x1 • Allows d/u measurement on a single proton! • Vector quark current! (electron is axial-vector) Souder, Londergan Charge Symmetry Violation at High x: clean observation possible For an isoscalar target like 2H Global fits allow x3 larger effects Conclusions & Perspectives

  32. A Vision for PV DIS Physics • solid angle > 200 msr • Count at 100 kHz • online pion rejection of 102 to 103 Souder • 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~0.75) • Moderate running times • CW 90 µA at 11 GeV • 40 cm liquid H2 and D2 targets • Luminosity > 1038/cm2/s Goal: Form a collaboration, start real design and simulations, and make pitch to US community at the next nuclear physics long range plan (2007) Conclusions & Perspectives

  33. Weak Neutral Currents and TeV Physics Beyond the Standard Model Conclusions & Perspectives

  34. Beyond Standard Model @ Low Q2 KK • Precise predictions @ 0.1% • Indirect access to TeV scale • World electroweak data has marginal 2, but no discernable pattern • Data used to put limits on energy scale of new physics effects • Parity-conserving contact interactions probed at 20-30 TeV level • Parity-violating contact interactions probed at 5-10 TeV level Conclusions & Perspectives

  35. SLAC E158 KK sin2eff = 0.2397 ± 0.0010 ± 0.0008 • APV = (-131 ± 14 ± 10) x 10-9 * Limit on LLL ~ 7 or 16 TeV * Limit on SO(10) Z’ ~ 1.0 TeV • * Limit on lepton flavor violating coupling ~ 0.01GF End of the SLAC Fixed Target Program Conclusions & Perspectives

  36. The LHC Erler • LHC to begin data collection in 2008 • Focus is on EW symmetry breaking • Standard Model Higgs hard below 150 GeV and above 500 GeV • Energy frontier: look for the unexpected • The unexpected at LHC likely to remain ill-defined! • The more obscure the signal, the more important are low energy constraints! • Electroweak Physics at the LHC • Factor of 3 improvement in W Mass • Factor of 5 improvement in Top Mass • Weak Mixing Angle: Improve constraints on new parity-conserving contact interactions Conclusions & Perspectives

  37. Qweak at JLab Page Region 2: Horizontal drift chamber location Region 1: GEM Gas Electron Multiplier Quartz Cerenkov Bars (insensitive to non-relativistic particles) Mini-torus e- beam MNC Lumi Monitors C1i’s measured to unprecedented precision QTOR Magnet Region 3:Vertical Drift chambers Collimator System Trigger Scintillator • Design, simulation, prototyping, construction • Installation in 2009 • Complementary to LHC • Important constraint should LHC see anomaly Conclusions & Perspectives

  38. Beyond SM with PV DIS For an isoscalar target like 2H, structure functions largely cancel in the ratio: (Q2 >> 1 GeV2 , W2 >> 4 GeV2, x ~ 0.3-0.5) Zheng, Reimer Complementary to LHC • Need to characterize nucleon structure at high-x to high precision • 6 GeV experiment launches PV DIS measurements at JLab • 12 GeV experiment requires tight control of normalization errors • Important constraint should LHC see anomaly Conclusions & Perspectives

  39. Møller Scattering @ 12 GeV Mack • Comparable to single Z pole measurement: shed light on disagreement • Best low energy measurement until ILC or -Factory • Could be done ~ 2012-13 Z pole asymmetries Address longstanding discrepancy between hadronic and leptonic Z asymmetries Conclusions & Perspectives

  40. Ultrahigh Precision at ILC KK Measure contribution from scalars to oblique corrections t new H physics b Z (world average ~0.00016) Critical crosscheck ALR and MW at future colliders: K.K, Snowmass 96 Systematics extremely challenging! Energy scale to 10-4, polarimetry to 0.15% Møller scattering at the ILC • Fixed target has advantages for systematics • Could work with ILC “exhaust”beam Conclusions & Perspectives

  41. Theoretical Challenges • Hadron Structure Theory (A. Schäfer) • Era of precision QCD requires major effort • Examples of NNLO convergence (e.g. DVCS) • Lattice QCD should enter the realm of dynamical chiral quarks • Balanced effort in perturbative QCD, chiral perturbation theory and Lattice QCD • Low Energy EW Measurements & Loops (W. Marciano) • Gamma-Z and Gamma-W boxes for semi-leptonic processes • Improved calculation of super-allowed beta decays • Future applications: APV, neutrino scattering… • Future Directions (M. Ramsey-Musolf) • Probing higher-twist effects in PVDIS: precision measurements with improved leading-twist predictions • EFT approach to few-body hadronic parity violation • SUSY implications of precision low energy EW measurements • CP and T violation probes via EDM with implications for dark matter and the primordial baryon asymmetry Conclusions & Perspectives

  42. Parity Violating Electron Scattering Experimental Challenges Conclusions & Perspectives

  43. Polarized Source Controls Lock- in Pulser Sw. diode-laser Movable Detektor with pinhole PC Aulenbacher, Pashke 5*Dx’ micron Grand average: ~ 1 nm 4*DE/E 4*ppm Grand average: ~ 0.25 ppb HAPPEX Position Differences during run with hydrogen target More and more demanding and ambitious with every run! Conclusions & Perspectives

  44. Cryogenic Targets E158 at SLAC G0 target at Jlab Requirements are becoming ever-demanding! Conclusions & Perspectives

  45. Polarimetry Hydrogen: 86.7% ± 2% Diefenbach, Mack Signal from A4 Compton Polarimeter HAPPEX Hydrogen Run • High future demands for sub-1% polarimetry: Critical to have redundancy • Promising techniques: “high-field” Moller and Atomic Hydrogen polarimetry Conclusions & Perspectives

  46. Where are we going? Electroweak Physics Valence Quark Physics Atomic Physics Nuclear Physics Nucleon Physics We will continue to learn a whole lot along the way Conclusions & Perspectives

  47. Personal Thoughts Studies of Weak Neutral Current Interactions touches on extraordinarily rich and diverse topics We learn to appreciate physics over all length scales and there is much left to learn over the full range What strikes me in these PAVI meetings is that the participants are not particle or nuclear or atomic physicists We are physicists I look forward to many more rewarding interactions with you at the next PAVI!!! Conclusions & Perspectives

  48. Not into the sunset! Conclusions & Perspectives

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