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Status Report of the measurement of G E n via 3 He(e,e ´ n)

Status Report of the measurement of G E n via 3 He(e,e ´ n). Robert J. Feuerbach The College of William and Mary for the E02-013 Collaboration. Elastic EM Form Factors. For an extended spin-1/2 particle, the general vertex term is:. Elastic cross-section:.

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Status Report of the measurement of G E n via 3 He(e,e ´ n)

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  1. Status Report of the measurement of GEn via 3He(e,e´ n) Robert J. Feuerbach The College of William and Mary for the E02-013 Collaboration

  2. Elastic EM Form Factors For an extended spin-1/2 particle, the general vertex term is: Elastic cross-section: Or in terms of the Sachs Form factors: Dominate at large Q2 January 4, 2006 Hall A Collaboration Meeting

  3. Double Polarization Measurement January 4, 2006 Hall A Collaboration Meeting

  4. Exclusive QE scattering: 3He(e,e’n) n E02-013 Setup scintillator ~85% polarization ~50% veto e e’ January 4, 2006 Hall A Collaboration Meeting

  5. 75 msr BB, ~100 msr ND Ltotal ~ 5·1036/(cm2 s)Len ~ 5·1035/(cm2 s) BB trigger ~ 2.3 kHzND trigger ~ 2.5 MHz MWDC ~ 2.6 MHz/uA 20 MHz per plane Target polarization ~50% Beam polarization ~84% Electronic LT ~ 82% DAQ LT ~ 84% Average 4 extra hits per plane affected tracking (See Seamus’s talk Saturday) Running conditions January 4, 2006 Hall A Collaboration Meeting

  6. Assignments January 4, 2006 Hall A Collaboration Meeting

  7. Electron arm reconstruction • Preshower/shower selects electrons well • Momentum σ ~.9%@ 1.3 GeV/c on average • VertexZ σ~ 4mm • “super-elastics” due to imperfect optics • Scintillator σt ~ 360ps January 4, 2006 Hall A Collaboration Meeting

  8. Neutron Detector • Data shown are from an analysis of the 1.8 GeV2 dataset. • Neutron Detector timing resolution of σ ~ 400ps • Neutrons/Charged particles differentiated by matching hits in Veto to clusters in the ND. • 1/β calculated from time of hit at ND and Rf-corrected time from BB scintillators. 3He(e, e’ A) – all charged ND-particle events protons Fast pions/muons? January 4, 2006 Hall A Collaboration Meeting

  9. QE Event Selection • Use missing 3-momentum to select QE events January 4, 2006 Hall A Collaboration Meeting

  10. QE Event selection: Protons Nuclear effects (FSI) can distort the observed asymmetry … Pperp < 150 MeV/c Momentum distributionof nucleons in 3He January 4, 2006 Hall A Collaboration Meeting

  11. QE Event selection: Neutrons Neutrons AccidentalBackground January 4, 2006 Hall A Collaboration Meeting

  12. QE Event selection: Neutrons Accidental Background January 4, 2006 Hall A Collaboration Meeting

  13. Rough Asymmetries @ Q2 = 1.8 GeV2 Integrated Asymmetries (NOT corrected for many several %-size effects) for different Beam ½-wave plate settings and Target polarization direction changes. • Yet need to account for distortion of the asymmetry from • False asymmetries:Electronic LT (~.5%)Tracking eff (~.2%?) DAQ livetimes(<.1%) Beam Charge (<.02%) • Finite acceptance • Dilution factors from N2 proton mis-ID January 4, 2006 Hall A Collaboration Meeting

  14. Projected Results Projected error bars assumeresults match theGalster parameterization. Systematic uncertainties for highest Q2 point still smaller than shown statistical uncertainty. January 4, 2006 Hall A Collaboration Meeting

  15. The Future: GEn @ 4.5 GeV2? • E0=3.7 GeV/c, E’=1.3 GeV/c, θBB=59° to measure GEn/GMn @ 4.5 GeV2 (limit of CLAS data on GMn). • Add shielding along beamline for the ND: reduces its rate by factor of 2. • Larger cell size to remove halo effects: drop overall rate factor 3. • Triple Ib to 24uA  Len~1.5 1036 /(s cm2). • A measurement with the 20% relative statistical uncertainty (vs. 14% at 3.4 GeV2) could be done in 500hrs (25 days). January 4, 2006 Hall A Collaboration Meeting

  16. Summary • Electron and neutron detector analysis is well understood, though still being “tweaked” • Can identify quasi-elastic proton and neutron events to extract the asymmetry and GEn. • Presently analyzing the 1.8 GeV2 dataset to identify problem areas: so far found electronic deadtime and tracking eff. (surprises), and proton mis-ID to be leading corrections. • Plan to complete 1.8 GeV2 analysis this spring, and results from all datasets by late 2007/early 2008 (my estimate). • Investigating measurement at 4.5 GeV2 ? January 4, 2006 Hall A Collaboration Meeting

  17. Backup slides January 4, 2006 Hall A Collaboration Meeting

  18. Proton Asymmetry January 4, 2006 Hall A Collaboration Meeting

  19. Background Asymmetry January 4, 2006 Hall A Collaboration Meeting

  20. Data Quality Beam polarization ~84% Target polarization ~50% IN BEAM • The experiment ran for 3 months in Spring 2006. • Four datasets (Q2=1.4, 1.8, 2.4, 3.4 GeV2) were taken. • Commissioned BigBite precision detector package, BigHand, hybrid cell and advanced optics system for the target. • Novel holding field magnet and compass to control and understand field gradients at the target. (Q2~3.5 GeV runs) January 4, 2006 Hall A Collaboration Meeting

  21. World data on GEn January 4, 2006 Hall A Collaboration Meeting

  22. Data Analysis • “Results” shown are from an advanced preliminary analysis of the 1.8 GeV2 dataset. • “Neutrons” are ALL clusters in BigHand without matching veto hits (very loose criteria for now). • Achieved momentum resolution from BB of dp/p~0.8%, BigHand timing resolution of 400ps (sigma) 3He(e, e’ N) January 4, 2006 Hall A Collaboration Meeting

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