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Parity-Violating Electron Scattering at JLab

Parity-Violating Electron Scattering at JLab. David S. Armstrong College of William & Mary. (replacing Juliette Mammei , who kindly provided most of the slides). MENU 2013 Rome, Italy Oct 2 2013. Parity-Violating Electron Scattering at JLab. Electroweak interaction (neutral current)

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Parity-Violating Electron Scattering at JLab

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  1. Parity-Violating Electron Scattering at JLab David S. Armstrong College of William & Mary (replacing Juliette Mammei, who kindly provided most of the slides) MENU 2013 Rome, Italy Oct 2 2013

  2. Parity-Violating Electron Scattering at JLab • Electroweak interaction (neutral current) • - not one of the canonical probes for Hadron Physics • (i.e. strong or electromagnetic) • - nevertheless, much of the program should be • of interest to this community • Focus today: • - new results since MENU2010 • - plans for 12 GeV era at Jefferson Lab

  3. Outline Intro to Parity-Violating Electron Scattering (PVES) The Vector Strange Form Factors a ≈ completed program Qweak: first results on the proton’s weak charge Neutron radius in Heavy Nuclei 5) Standard Model Tests with PVES: plans at JLab-12 GeV

  4. • Neutrino mass and their role in the early universe 0νββ decay, θ13 , β decay,… • Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0νββ, θ13 • Unseen Forces of the Early Universe Weak decays, PVES, gμ-2,… LHC new physics signals likely will need additional indirect evidence to pin down its nature • Neutrons: Lifetime, P- & T-Violating Asymmetries (LANSCE, NIST, SNS...) • Muons: Lifetime, Michel parameters, g-2, Mu2e (PSI, TRIUMF, FNAL, J-PARC...) •PVES: Low-energy weak neutral current couplings, precision weak mixing angle (SLAC, Jefferson Lab, Mainz) new since MENU2010: first result from QWeak 2) Study nucleon and nuclear properties • Strange quark content of nucleon new since MENU2010: HAPPEX-III • Neutron radius of heavy nuclei new since MENU2010 – first PREx results 1) Search for physics Beyond the Standard Model • Low energy (Q2 <<M2) precision tests complementary to high energy measurements MENU 2013

  5. A brief history of parity violation 1930s – weak interaction needed to explain nuclear β decay 1950s – parity violation in weak interaction; V-A theory to describe 60Co decay R L L R 1970s – neutral weak current events at Gargamelle late 1970s – parity violation observed in electron scattering - SLAC E122 MENU 2013

  6. Parity-violating electron scattering 2 Electroweak interference MENU 2013

  7. SLAC Experiments • SLAC E122 – crucial confirmation of WSG electroweak model • Electron-deuteron deep inelastic scattering • High luminosity: photoemission from NEA GaAs cathode • Rapid helicity-flip (sign of e- polarization) • Polarimetry to determine beam polarization • Magnetic spectrometer: backgrounds and kinematic separation APV ~ 100 ± 10 ppm sin2θW=0.20±0.03 • SLAC E158 – 1999 • electron-electron scattering - purely leptonic interaction • electron-electron weak attractive force had never been measured! APV ~ -131 ± 14 ± 10 ppb sin2θW=0.2403±0.0013 MENU 2013

  8. Genesis of a Strange Idea Puzzle: Initial DIS measurements of spin-structure of nucleon (EMC): valence quarks contribute unexpectedly low fraction to total spin - “Spin Crisis” Possible reconciliation: large fraction of spin from ? eg. D. B. Kaplan and A. Manohar, Nucl. Phys. B310, 527 (1988). Theoretical realization: not only did many available nucleon model calculations allow this, but they also allowed (and in some cases favored) large strange quark contributions to other properties of nucleon. Consternation and excitement: at the time, data gave no constraint on strange contributions to charge distribution and magnetic moment! Challenge: how to isolate strange vector form factors? Answer: exploit the weak neutral current as a probe

  9. strangequark contribution Assume isospinsymmetry, and we have this and this are well known what about this? (Assume neutral weak charges are known) 10/2/2013 MENU 2013

  10. Nucleon Form Factors NC and EM probe same hadronic flavor structure, with different couplings: Assume Charge Symmetry:

  11. Strange Form Factors MENU 2013

  12. Qweak: Proton’s weak charge • Neutral current analog of electric charge: The Standard Model makes a firm prediction of “Accidental suppression” sensitivity to new physics Note: Q-weak is particularly sensitive to the quark vector couplings ( and ) . MENU 2013

  13. Qweak: Proton’s weak charge For electron-quark scattering: Use four-fermion contact interaction to parameterize the effective PV electron-quark couplings (mass scale and coupling) New physics: Small θ Large θ Planned 4% measurement of proton’s weak charge - probes TeV scale new physics new Z', leptoquarks, SUSY ... Erler, Kurylov, and Ramsey-Musolf, PRD 68, 016006 2003 MENU 2013

  14. Extracting the weak charge Hadron structure enters here: electromagnetic and electroweak form factors… Data rotated to Reduced asymmetry more convenient: One must extrapolate to . We measure at . SM Qweak kinematics Hadronic term extracted from fit The previous strange form factor program (experiments at MIT/Bates, JLab and MAMI) allow us to subtract our hadronic contribution MENU 2013

  15. The Qweak Apparatus Main detectors 8-fold symmetry QTOR Cleanup collimators QTOR Shield wall Acceptance defining collimator Trigger scintillator Lead collar Vertical drift chambers (VDC) (rotate) e- beam e- beam Target Tungsten plug Horizontal drift chambers (HDC) (rotate) Lintels MENU 2013

  16. Reduced Asymmetry 4% of total data in the forward-angle limit (θ=0) Hadronic part extracted through global fit of PVES data. MENU 2013 MENU 2013

  17. The C1q & the neutron’s weak charge MENU 2013

  18. The C1q & the neutron’s weak charge Combining this result with the most precise atomic parity violation experiment we can also extract, for the first time, the neutron’s weak charge: MENU 2013

  19. Qweak – first result First result (4% of data set): ppb Lots of work to push down systematic errors, but no show-stoppers found…. Expect final result in 12-18 months time. More details: Fundamental Symmetries 3, this afternoon MENU 2013

  20. A of Auxiliary Measurements Qweak has data (under analysis) on a variety of observables of potential interest for Hadron physics: • Beam normal single-spin asymmetry* for elastic scattering on proton • Beam normal single-spin asymmetry for elastic scattering on 27Al • PV asymmetry in the region. • Beam normal single-spin asymmetry in the region. • Beam normal single-spin asymmetry near W= 2.5 GeV • Beam normal single-spin asymmetry in pionphotoproduction • PV asymmetry in inelastic region near W=2.5 GeV (related to box diagrams) • PV asymmetry for elastic/quasielastic from 27Al • PV asymmetry in pionphotoproduction • *: aka vector analyzing power aka transverse asymmetry; • generated by imaginary part of two-photon exchange amplitude • (paceWim van Oers) MENU 2013

  21. Neutron skin – PREx Exploit the large weak charge of neutron to extract radius of neutron distribution in heavy nucleus; theoretically clean probe. 208Pb 208Pb 208Pb 2 First result of PRExexperiment at JLab: PRL 108(2012)112502 APV = 0.656 ± 0.060 (stat) ± 0.014 (syst) ppm MENU 2013

  22. PREX, PREX II and CREX 208Pb more closely approximates infinite nuclear matter The 48Ca nucleus is smaller, so APV can be measured at a Q2 where the figure of merit is higher and are expected to be correlated, but the correlation depends on the correctness of the models The structure of 48Ca can be addressed in detailed microscopic models PREX-II (proposed) Measure both and - test nuclear structure models over a large range of A More info: yesterday’s talks by G. Urcioli and M. Thiel in Fundamental Symmetries 2 Theory from P. Ring et al. Nucl. Phys. A 624 (1997) 349 MENU 2013

  23. Future: PVES at JLab in 12 GeV era MOLLER - precision Standard Model test by measuring weak charge of electron in PV electron-electron scattering (revisit SLAC E158) SOLID - precision Standard Model test by measuring PV DIS on deuteron: access the quark weak axial couplings C2q (also – a similar measurement was made at 6 GeV in Hall A at Jefferson Lab, X. Zheng et al., being readied for publication, but I’m not authorized to show the results; stay tuned…) Large kinematic coverage: disentangle CSV and higher-twist effects MENU 2013

  24. MOLLER at 12 GeV Coupling constants Mass scale 2.3% MOLLER uncertainty e- e- LEP2 (gLR and sum) mass scale sensitivity ~5.2 and 4.4 TeV e- e- Doubly-charged scalar, heavy Z’, SUSY, dark Z… Lepton compositeness – strong coupling – 47 TeV MENU 2013

  25. MOLLER and weak mixing angle Reminder: at tree-level QWe = (1 – 4 sin2θW) Higgs discovery at LHC allows firm prediction of MOLLER asymmetry in Standard Model MENU 2013

  26. MOLLER and weak mixing angle MENU 2013

  27. The MOLLER Experiment Detector Array Hybrid Torus Upstream Torus Scattering Chamber Target Collimators 28 m Incoming Beam MENU 2013

  28. e- SOLID – accessing the C2q’s e- Z* γ* N X Cahn and Gilman, PRD 17 1313 (1978) polarized electrons on deuterium MENU 2013

  29. Red ellipses are PDG fits Blue bandsrepresent expecteddata: Qweak (left) and PVDIS-­6GeV (right) Green bandsare proposed SOLID PVDIS Small θ Large θ MENU 2013

  30. SOLID – Large Acceptance Device MENU 2013

  31. SOLID – Parity-Conserving Physics - SIDIS with Transversely Polarized 3He approved 90 days - SIDIS with Longitudinally Polarized 3He approved 35 days - SIDIS with Transversely Polarized Proton approved 120 days - Near Threshold Electroproduction of J/Psi approved 60 days PVDIS approved for 169 days (half of full request) MENU 2013

  32. PVES Experiment Summary MENU 2013

  33. Summary • Strange vector form factors of proton – small, consistent with zero. • Qweak: First measurement of proton’s weak charge, consistent with Standard Model, 25x more data on tape • PREx: two-sigma evidence for neutron “skin” of 208Pb; will improve after • JLab comes online after 12 GeV upgrade, and will extend to 48Ca • MOLLER and SOLID: major programs after JLab upgrade • two complementary Standard Model tests. Grazie to the MENU 2013 organizers for inviting Juliette Mammei to give this talk, and for accepting me as a poor substitute…. MENU 2013

  34. Extra slides MENU 2013

  35. Qweak and weak mixing angle MENU 2013

  36. SLAC Experiment E122 Polarimetry • High luminosity from photoemission from NEA GaAscathode • Rapid helicity-flip (sign of e- polarization) Integrating detectors Magnetic spectrometer Background and kinematic separation Huge achievement! Highest P2Iever, by far. Developed forthisexperiment at SLAC and used eversince MENU 2013

  37. SLAC Experiment E122 Parity Non-Conservation in Inelastic Electron Scattering, C.Y. Prescott et. al, 1978 APV ~ 100 ± 10 ppm sin2θW=0.20±0.03 GWS --‐ Nobel Prize 1979 Deep inelastic scattering: Y dependence reflects quark axial/electron vector coupling strength At high x MENU 2013

  38. Complementary to the LHC - Z΄ Assume LHC discovers a new spin 1 gauge boson with M =1.2 TeV If the SM value is measured MOLLER can distinguish between models Erler and Rojas Half-way betweenSM and E158 central value MENU 2013

  39. Isolating strange form factors Backward angle Forward angle For a proton: ~ few parts per million For 4He: GEs alone For deuteron: enhanced GAe sensitivity MENU 2013

  40. Electroweak Radiative Corrections

  41. Electroweak Radiative Corrections

  42. Transverse Asymmetry Measurement Normal production running: 89% longitudinal beam polarization Small amount of transverse polarization • Large parity conserving asymmetry (~5ppm) • Leaks into the experimental asymmetry through broken azimuthal symmetry Measurements of the Beam Normal Single Spin Asymmetry (BNSSA) provide: • Direct access to imaginary part of two-photon exchange We need to correct for this… Horizontal and vertical components measured separately Detector number

  43. Transverse Asymmetry Measurement Normal production running: 89% longitudinal beam polarization Small amount of transverse polarization • Large parity conserving asymmetry (~5ppm) • Leaks into the experimental asymmetry through broken azimuthal symmetry PhD thesis of BuddhiniWaidyawansa; being prepared for publication ppm This is the most precise measurement of Beam Normal Single Spin Asymmetry to date.

  44. Global PVES Fit Details □γZ RC • 5 free parametersalaYoung, et al. PRL 99, 122003 (2007): • Employs all PVES data up to Q2=0.63 (GeV/c)2 • On p, d, & 4He targets, forward and back-angle data • SAMPLE, HAPPEX, G0, PVA4 • Uses constraints on isoscalar axial FF • Zhu, et al., PRD 62, 033008 (2000) • All data corrected for E & Q2 dependence of • Hall et al., arXiv:1304.7877 (2013) & Gorchtein et al., PRC84, 015502 (2011) • Effects of varying Q2, θ, & λ studied, found to be small

  45. MENU 2013

  46. Qweak “Run 0” corrections and their corresponding sizes Target aluminum windows are our largest (~30%) correction Beam line background is currently our largest uncertainty

  47. MOLLER SLHC, 1 ab-1 F. Petriello et al, PRD 80 (2009) MOLLER: if Z‘seen at LHC... • Virtually all GUT models predict new Z’s (E6, SO(10)…): • LHC reach ~ 5 TeV • With high luminosity at LHC, 1-2 TeV Z’ properties can be extracted Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC… LHC data can extract the mass, width and AFB(s) MOLLER: resolve signs on eR, eL

  48. MOLLER MSSM RPV SUSY Ramsey-Musolf and Su, Phys. Rep. 456 (2008) MOLLER: if SUSY seen at LHC... MSSM sensitivity if light super-partners and large tan β

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