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Results from the G 0 Measurement

Results from the G 0 Measurement. Parity-violating electron scattering from the nucleon Hydrogen and deuterium targets Strange quark contributions to electromagnetic form factors. Colleen Ellis, University of Maryland.

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Results from the G 0 Measurement

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  1. Results from the G0 Measurement • Parity-violating electron scattering from the nucleon • Hydrogen and deuterium targets • Strange quark contributions to electromagnetic form factors Colleen Ellis, University of Maryland • 1988 Kaplan and Manohar—sea quark contributions to ground state nucleon properties, • i.e. spin, charge, and magnetic movements from neutral weak probes ( νN scattering) • 1989 McKeown then Beck outlined a PVES program that could measure strange quark • contributions to the proton’s charge and magnetism. D.Kaplan and A.V. Manohar, Nucl. Phys. B310, 527 (1988) R.D. McKeown, Phys Lett. B219, 140 (1989) D.H. Beck, Phys. Rev. D39, 3248 (1989)

  2. Parity Violating elastic e-N scattering charge symmetry Access via form factors: contribution to nucleon charge and magnetism Q2 behavior well-understood Measured in G0

  3. Parity Violating elastic e-N Form Factors PV asymmetries from EM and weak interference terms can be varied between zero and unity for a fixed Q2 by varying the beam energy and electron scattering angle. Two kinematics, two targets gives 3 linear combinations of EM and weak form factors

  4. + + Axial form factor seen by PV electron scattering (hFAg+ Re) at Q2=0 computed by Zhu etal, PRD 62 (2000) 033008 SAMPLE deuterium asymmetry data agree well but Q2 behavior is not well constrained slide thanks to E. Beise

  5. Asymmetries to Form Factors • Electromagnetic form factors: Kelly (PRC70 (2004)) • does not include new low Q2 data from BLAST or JLab • eventually use new fits (Arrington & Melnitchouk for p, Arrington & Sick for n) • differences in fits become 0.5 – 1 % in the asymmetry • also used in Schiavilla calculation for D • (see Diaconescu, Schiavilla & van Kolck, PRC 63 (2001) 044007) • Two-boson exchange corrections to Asymmetry: 0.5 -1.2% • (see Tjon, Blunden & Melnitchouk, arXiv:0903.2759v1)

  6. AF 79.39 42.87 2.46 -23.68 AB 21.57 62.84 12.10 -38.28 Ad 12.12 12.49 9.50 -53.29 G0 –Path to extracting vector form factors At Q2 = 0.62 and 0.23 (GeV/c)2, there are three measurements: AF: forward angle H (recoil protons) (D.S. Armstrong, et al., PRL 95, 092001 (2005)) AB : backward angle H(D. Androic, et al., PRL 104, 012001 (2010)) Ad : backward angle D a2 (ppm) a3 (ppm) a0 (ppm) a1 (ppm) at Q2 = 0.62 GeV2

  7. G0 Forward Angle Experiment • Forward angle measurement completed May 04 • LH2 target, detect recoil protons • Q2 = 0.12-1.0 (GeV/c)2, E=3.03GeV • Spectrometer sorts protons by Q2 in focal plane detectors (16 rings in total) • Detector 16: “super-elastic”, crucial for measuring the background • Beam bunches separated by 32 ns • Time-of-flight separates protons from pions • Results published in : • D.S. Armstrong, et al., • PRL 95, 092001 (2005)

  8. G0 Forward angle Results EM form factors: J.J.Kelly, PRC 70, 068202 (2004) G0 Backward HAPPEX-3 D.S. Armstrong et al., PRL 95 (2005) 092001

  9. CED+ Cherenkov FPD e- beam target e- beamline G0Backward Angle • Hydrogen and deuterium targets • Electron beam energy : • 362 MeV : Q2=0.23 GeV2 • 687 MeV : Q2=0.62GeV2 • Completed running in March 2007 • Particle detection and identification : • 16 Focal Plan Detectors • 9 Cryostat Exit Detectors elastic and inelastic electron separation • Čerenkov detectors electron and pion separation

  10. 687 MeV Møller Results April 2006 March 2007 Sep.-Dec. 2006 Polarized Beam Properties • Measurements of Møller asymmetry at 687 MeV • Mott scattering for 362 MeV measurements • Mott asymmetry measured at 5 MeV in injector • New work on effect of background improves agreement with Møller 10 Pe(687 MeV) = 85.78 ± 0.07 ± 1.38% Pe(362 MeV) = ± 2.05%

  11. Hydrogen raw electron data d 362 MeV blinded raw asymmetries (ppm) Hz/uA octant # (azimuthal distribution) 687 MeV Hz/uA 11

  12. Deuterium raw electron data 362 MeV Hz/uA d blinded raw asymmetries (ppm) octant # (azimuthal distribution) 687 MeV d Hz/uA 12

  13. Analysis Strategy Blinding Factors × 0.75-1.25 Unblind H, D Raw Asymmetries, Ameas ~10-50 ppm Corrections Scaler counting correction Rate corrections from electronics Helicity-correlated corrections Background corrections Beam polarization < 1% of Aphys < 0.1 ppm 4% on asymmetry P= 0.8578 ± 0.0007 (stat) ± .014 (sys) Electromagnetic radiative corrections (from simulation) Q2 Determination (from simulation) H, D Physics Asymmetries, Aphys ± 0.003 GeV2 13

  14. Cerenkov Trigger CFD MT Coincidence 1 CED 1 FPD 1 Trigger CFD electron Trigger CEDxFPD CFD MT CFD pion Rate Corrections • Correct the yields for random coincidences and electronic dead time prior to asymmetry calculation • Randoms small except for D-687 (due to higher pion rate) • Direct (out-of-time) randoms measured • Validated with simulation of the complete electronics chain CED FPD 14

  15. Backgrounds: Magnetic Field Scans D-687 CED 7, FPD 13 Use simulation shapes to help determine dilution factors Main contributions are Aluminum windows (~10%), pions (for D-687 data only). 15

  16. Experimental “Physics” Asymmetries all entries in ppm Largest correction is due to the 85% beam polarization --dominates H systematic uncertainties --for D-687, contributes about equally with rate corrections to the systematic uncertainty

  17. Form Factor Results • Using interpolation of G0 forward measurements G0 forward/backward G0 forward/backward Global uncertainties PVA4: PRL 102 (2009) Some calculations: Leinweber, et al. PRL 97 (2006) 022001 Leinweber, et al. PRL 94 (2005) 152001 Wang, et al arXiv:0807.0944 (Q2 = 0.23 GeV2) Doi, et al, arXiv:0903.3232 Q2 = 0.1 GeV2 combined (G0,HAPPEX, SAMPLE & PVA4) SAMPLE Zhu, et al. PRD 62 (2000) 17

  18. Summary • Q2 behavior of strangeness contribution to proton’s charge and magnetism: continue to be small • first results for the Q2 behavior of the anapole contributions to the axial form factor • other results to come soon from G0: • transverse beam spin asymmetries (2-gexchange) in H and D • PV in the N-D transition: axial transition f.f. • PV asymmetry in inclusivep-production

  19. The G0 Collaboration (backward angle run) Caltech, Carnegie Mellon, William and Mary, Hendricks College, Orsay, Grenoble, LA Tech, NMSU, Ohio, JLab, TRIUMF, Illinois, Kentucky, Manitoba, Maryland, Winnipeg, Zagreb, Virginia Tech, Yerevan Physics Institute PhD students: C. Capuano, A. Coppens, C. Ellis, J. Mammei, M. Muether, J. Schaub, M. Veerstegen, S. Bailey Analysis Coordinator: F. Benmokhtar

  20. Backups

  21. Elastic Region: G0 Inelastic Region: N D G0: N→  • Measurement: Parity-violating asymmetry of electrons scattered inelastically • ANΔ gives direct access to GANΔ • Directly measure the axial (intrinsic spin) response during N →Δ+ transition • Will find GANΔ over a range of Q2 • 0.05 GeV/c2 < Q2 < 0.5 GeV/c2. • First measurement in neutral current process • Data: Inelastic electrons measured by G0 • Scattered from both LH2 and LD2, each at two energies (362MeV & 687MeV) IN Asymmetry (ppm) vs Octant (LH2 @ 687MeV) OUT Asymmetry (ppm) BLINDED Octant Raw Asymmetry (averaged over inelastic region)

  22. Transverse Asymmetry 2 photon exchange Inclusion of the real part of the 2γ exchange in the cross section may account for the difference between measurements of GE/GM from unpolarized cross section and polarization transfer measurements It also tests the theoretical framework that calculates the contribution of γZ and W+W- box diagrams that are important corrections to precision electroweak measurements

  23. Asymmetry Uncertainties--Hydrogen, 687 MeV

  24. Asymmetry Uncertainties--Deuterium, 687 MeV

  25. Correction due to misidentified pions • 3 Ways to calculate • runs with special beam structure providing timing reference allowing particle TOF • PMT Multiplicity (two versus three of the cerenkovPMT’s firing) • Pulse heights (waveform digitized) cerenkov detector 4 pmts 687 MeV red: pions blue: electrons counts aerogel p- contamination to electron yield (Ap~ 0) D 362: 0.5% D 687: 4% # single photo electrons threshold 25

  26. D asymmetries: Calculation provided by Rocco Schiavilla (see Diaconescu, Schiavilla & van Kolck, PRC 63 (2001) 044007) absorbs isoscalar axial term broken down by isospin

  27. Quasielastic PV (ee’) in Deuterium Use Quasielastic scattering from deuterium as lever arm for GAe(Q2) Parity conserving nuclear corrections to the asymmetry are generally small, 1-3% at backward angles. Calculation provided to us by R. Schiavilla includes final state interactions and 2-body effects. Diaconescu, Schiavilla + van Kolck, PRC 63 (2001) 044007 Schiavilla, Carlson + Paris, PRC 67 (2003) 032501 See also Hadjimichael, Poulis + Donnelly, PRC45 (1992) 2666 Schramm + Horowitz, PRC 49 (1994) 2777 Kuster + Arenhovel, NPA 626 (1997) 911 Liu, Prezeau, + Ramsey-Musolf, PRC 67 (2003) 035501 E. Beise, U Maryland

  28. Deuterium model comparison to cross section data calculation from R. Schiavilla see also R.S., J. Carlson, and M. Paris, PRC70, 044007 (2004). • AV18 NN potential • relativistic kinematics • J.J. Kelly fit to nucleon • form factors data from: S. Dytman, et al., Phys. Rev. C 38, 800 (1988) B. Quinn, et al., Phys. Rev. C 37, 1609 (1988) E. Beise, U Maryland

  29. 2-body effects in the D asymmetry calculations from R. Schiavilla, see also R.S., J. Carlson, and M. Paris, PRC70, 044007 (2004). leading term of the asymmetry axial form factor coefficient has ~15% correction from 2-body effects E. Beise, U Maryland

  30. Scaler Counting Issue with Electronics • Electronics sorts detector coincidences (CEDi and FPDj) into separate scaler channels • FPGA-based system in North American electronics (4 octants) • Because of error in FPGA programming, two short (~3 ns) pulses could be sent to scaler in < 7 ns • ~ 1% of events have such miscounts • Such pulse pairs can cause scaler to drop or add bits • Detailed simulation of ASIC with propagation delays between (flip flop) elements • Effect on asymmetry is <0.01 Aphys • Test by cutting data; compare with French octants Data Simulation 30

  31. The Gzero Collaboration College of William and Mary, Institut de Physique Nucléaire d'Orsay, Yerevan Physics Institute, Laboratoire de Physique Subatomique et de Cosmologie Grenoble, University of Illinois, University of Maryland, Thomas Jefferson National Accelerator Facility, University of Manitoba, Carnegie Mellon University, California Institute of Technology, University of Kentucky, TRIUMF, Louisiana Tech University, Virginia Tech, University of Northern British Columbia, New Mexico State University ,University of Winnipeg, Ohio University, Hampton University, Hendricks College, University of Zagreb U.S. G0 participation jointly supported by DOE and NSF. Significant additional contributions to G0 from NSERC (Canada) and CNRS (FR)

  32. Summary of the G0 Backangle Run Run start to run end ~ 8940 hours Beise Run Coordinator report March 2007

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