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For the G 0 Collaboration:

Results from the Forward Angle Experiment  a Measurement of Strange EM Form Factors of the Nucleons. JLab E-00-006, D.H. Beck, spokesperon. Jianglai Liu Univ. of Maryland. For the G 0 Collaboration:.

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For the G 0 Collaboration:

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  1. Results from the Forward Angle Experiment  a Measurement of Strange EM Form Factors of the Nucleons JLab E-00-006, D.H. Beck, spokesperon Jianglai Liu Univ. of Maryland For the G0 Collaboration: Caltech, Carnegie-Mellon, William&Mary, Grinnell College, Hampton, IPN-Orsay, LPSN-Grenoble, JLab, Kentucky, LaTech, NMSU, TRIUMF, UIUC, U Manitoba, U Maryland, UNBC, U Winnipeg, VPI, Yerevan PANIC05, Santa Fe, NM Oct 24-28, 2005

  2. Flavor Decomposition of Nucleon Form Factors Proton and Neutron Electromagnetic Form Factors Strange quark E/M form factors Proton Weak Form Factors : Assume charge symmetry But how do we measure the GZ ????

  3. Parity Violation in the Elastic Electron Scattering forward ep backward ep backward ed kinematic factors Assuming EM and axial form factors are known (with errors), each measurement yield GEs+GMs where

  4. G0 Forward Angle Experiment • 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 14 acceptance: Q2 = 0.41,1.0 • Detector 15: Q2 = 0.44-0.88 • Detector 16: “super-elastic”, crucial for measuring the background • Time-of-flight separates protons from pions • Beam bunches separated by 32 ns • Forward angle measurment completed May 04

  5. Analysis Overview Blinding Factor Raw Asymmetries, Ameas Beam and instrumental corrections: Deadtime Helicity-correlated beam properties Leakage beam Beam polarization Background correction Aphys Unblinding GEs+GMs Q2 nucleon form factors

  6. 499MHz Leakage Beam Leakage demo, extreme case “G0” AQ = 1000 ppm “Leakage” AQ = -1000 ppm 0 16 32 ns • ~ 50 nA 499 MHz beam leaks into G0 beam (~ 40 uA) • Leakage current has large, varying asymmetry(A~ 600 ppm). BCM integrates charge, no sensitivity to the micro-structure! • Use “cut0” region in actual data to measure leakage current and asymmetry throughout run. Worked out nicely. Aleak = -0.710.14 ppm (global uncertainty!)

  7. Background Correction  Yield & Asymmetry “2-step” Fit constant quadratic 2/=31.1/40 2/=37.5/44 detector 8 • Extract bin-by-bin dilution factor fb(t) by fitting time-of-flight spectra (gaussian signal + 4nd order polynomial background) • Use results to perform asymmetry fit:Ae = const, Ab = quadratic

  8. Det. 15 Background Corrections • Elastic peak broadened (~6 ns) because of increased Q2 acceptance. • Smooth variation of the background yield and asymmetry over detector range 12-14, 16. So make linear interpretation over detector number to determine fb(t) and Ab(t). GEANT MC: background asymmetry arises from hyperon (0,+,0) weak decay-particles rescatter into the detectors.

  9. Elastic Asymmetries • “No vector strange” asymmetry, ANVS, is A(GEs,GMs = 0) • Nucleon EM form factors: Kelly PRC 70 (2004) 068202 • Inner error bars: stat; outer: stat & pt-pt sys • Primary contributors to the global error band: • Leakage correction (low Q2) • background correction (high Q2)

  10. GEs+GMs, Q2 = 0.12-1.0 GeV2 • “Model” uncertainty is the EW rad. corr. unc. Dominated by the uncertainty of GAe. • 3 nucleon form factor fits; spread indicate uncertainties. • |Kelly-FW| heavily driven by the difference in GEn. A 2 test based on the random and correlated errors: the non-vector-strangeness hypothesis is disfavored at 89%!

  11. World Data with G0 95.5% CL Q2=0.1 GeV2 Q2=0.48 GeV2 Strange quark contributes to p at -10% level.

  12. Speculations of the Q2 dependence of GEs & GMs For G0,  increases with Q2 Emerging picture: At low Q2 end, despite the small , the data are positive, consistent with a large and positive GMs. Data go toward zero around Q2~0.2, which suggests GEs might have a negative bump there. Data curve back up again for Q2>0.3 (note the growing ), indicating that GMs stays positive.

  13. Summary • The successful G0 forward angle experiment yield the first measurement of parity-violating asymmetries over broad Q2 range. PRL 95, 092001(2005) • World data: GMs and GEs are both likely nonzero • GMs large and positive at low Q2 • GMs might decrease with Q2, but stay positive up to Q2=1.0 (GeV/c)2 • GEs might have a negative bump at Q2~0.2 (GeV/c)2 • G0 H2/D2 backward angle runs in 2006 will enable a separation of GEs, GMs, and GAe… Stay tuned. We gratefully acknowledge the support from our funding agencies and the strong technical support from TJNAF and many other groups …. Doug Beck’s plenary talk (10 am, Oct 26): Overview of strangeness of the nucleon.

  14. Backup Slides

  15. The G0 Collaboration D.S.Armstrong1, J.Arvieux2, R.Asaturyan3, T.Averett1, S.L.Bailey1, G.Batigne4, D.H.Beck5, E.J.Beise6, J.Benesch7, L.Bimbot2, J.Birchall8, A.Biselli9, P.Bosted7, E.Boukobza2,7, H.Breuer6, R.Carlini7, R.Carr10, N.Chant6, Y.-C.Chao7, S.Chattopadhyay7, R.Clark9, S.Covrig10, A.Cowley6, D.Dale11, C.Davis12, W.Falk8, J.M.Finn1, T.Forest13, G.Franklin9, C.Furget4,D.Gaskell7, J.Grames7, K.A.Griffioen1, K.Grimm1,4,B.Guillon4, H.Guler2, L.Hannelius10, R.Hasty5, A. Hawthorne Allen14, T.Horn6, K.Johnston13, M.Jones7, P.Kammel5, R.Kazimi7, P.M.King6,5, A.Kolarkar11, E.Korkmaz15, W.Korsch11, S.Kox4, J.Kuhn9, J.Lachniet9, L.Lee8, J.Lenoble2, E.Liatard4, J.Liu6, B.Loupias2,7, A.Lung7, G.A.MacLachlan16, D.Marchand2, J.W.Martin10,17, K.W.McFarlane18, D.W.McKee16, R.D.McKeown10, F.Merchez4, H.Mkrtchyan3, B.Moffit1, M.Morlet2, I.Nakagawa11, K.Nakahara5, M.Nakos16, R.Neveling5, S.Niccolai2, S.Ong2, S.Page8, V.Papavassiliou16, S.F.Pate16, S.K.Phillips1, M.L.Pitt14, M.Poelker7, T.A.Porcelli15,8, G.Quéméner4, B.Quinn9, W.D.Ramsay8, A.W.Rauf8, J.-S.Real4, J.Roche7,1, P.Roos6, G.A.Rutledge8, J.Secrest1, N.Simicevic13, G.R.Smith7, D.T.Spayde5,19, S.Stepanyan3, M.Stutzman7, V.Sulkosky1, V.Tadevosyan3, R.Tieulent4, J.van de Wiele2, W.van Oers8, E.Voutier4, W.Vulcan7, G.Warren7, S.P.Wells13, S.E.Williamson5, S.A.Wood7, C.Yan7, J.Yun14 1College of William and Mary, 2Institut de Physique Nucléaire d'Orsay, 3Yerevan Physics Institute, 4Laboratoire de Physique Subatomique et de Cosmologie-Grenoble, 5University of Illinois, 6University of Maryland, 7Thomas Jefferson National Accelerator Facility, 8University of Manitoba, 9Carnegie Mellon University, 10California Institute of Technology, 11University of Kentucky, 12TRIUMF, 13Louisiana Tech University, 14Virginia Tech, 15University of Northern British Columbia, 16New Mexico State University, 17University of Winnipeg, 18Hampton University, 19Grinnell College

  16. G0 in Hall C superconducting magnet (SMS) Lumi monitors cryogenic supply beam monitoring girder scintillation detectors cryogenic target service module electron beamline

  17. Beam Performance All parameters converge to zero!

  18. Electronics Deadtime Corrections To the first order • This shows up as • a decrease of normalized yield with Ibeam (almost like a target density reduction) • a correlation between Am and AQ . • The DT effect is largely corrected based on the model of the electronics • The residual AQ correlation is removed by the linear regression • The final residual Aphys dependence is corrected based on Aphys and fresidual (~0.050.05 ppm).

  19. Helicity Correlated Beam Properties and Their Corrections So require • Small ΔPi • Small sensitivity to Pi • Azimuthal symmetry  large reduction of detector sensitivity to beam positions • Response of spectrometer to beam changes well understood • False asymmetries (and the uncertainty) due to helicity-correlated beam parameters very small (~-0.02 ppm)

  20. Results of the Hyperon Simulation Use KaonMAID as generator for 0,+, 0 Hyperon polarizations: Source explained; used measured data in the correction.

  21. Detector 15 Asymmetry Compare interpolated background asymmetry and data Assume elastic asymmetry in each bin is a constant. Take interpolated fb and Ab, fit three Ae.

  22. Summary of Systematic Effects

  23. Global Fits to World Data Toy model, minimal physics input à la Kelly dipole form • Kelly form ensures GEs(0)=0, GEs1/Q4 when Q2 large • Fixed b3 = 1, all other variables float • Fit all 24 data points: 18 G0, 3 HAPPEX, 2 A4, 1 SAMPLE

  24. Results of the fit Excellent fit 2 = 14.9 19 d.o.f. Correlation Coeff.

  25. GEs and GMs Separately • Compare GEs with GEn, and GMs with GMp • Remember the factor of -1/3 -1/3s/p = -18% -1/3GEs(0.2)/GEn(0.2)~40%

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