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 E Collaboration

E StatusJanuary 4, 2006 Hall A Collaboration Meeting 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 Q 2

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Double Polarization Measurement

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Exclusive QE scattering: 3 He(e,en) e n veto scintillator e E Setup ~85% polarization ~50%

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Running conditions 75 msr BB, ~100 msr ND L total ~ 5·10 36 /(cm 2 s) L en ~ 5·10 35 /(cm 2 s) BB trigger ~ 2.3 kHz ND 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 Seamuss talk Saturday)

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Assignments Analyze Q 2 =1.8 GeV 2 datasetAll the students Calibrate other datasetsND timing (Jon), BB scint. (Ameya), Shower/preshower (Sergey), beam Raster + DC offsets (Brandon) BB optics (Seamus), Target (Aidan) Analysis of all datasets: sharedEach student has 1-2 datapoints as primary responsibility, and one more as a check: each Q 2 has 3 students on it. Veto efficiency ( proton mis-ID)Jon ND stability over timeTim EPICs and Target conditions databaseBrandon Monte-Carlo for background studies (pion production, etc.) Gregg Franklin Overall Analysis softwareRob Finite acceptance effects (understood)Gregg ND documentation (~ done)Tim/Albert(geom), Rob(algorithms) BB geom and algorithms (~ done)Seamus Electronics config. doc. (~~ done)Sergey(BB), Alexandre(ND)

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Electron arm reconstruction Preshower/shower selects electrons well Momentum σ 1.3 GeV/c on average VertexZ σ ~ 4mm super-elastics due to imperfect optics Scintillator σ t ~ 360ps

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Neutron Detector Data shown are from an analysis of the 1.8 GeV 2 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. 3 He(e, e A) – all charged ND-particle events protons Fast pions/muons?

E StatusJanuary 4, 2006 Hall A Collaboration Meeting QE Event Selection Use missing 3-momentum to select QE events

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

E StatusJanuary 4, 2006 Hall A Collaboration Meeting QE Event selection: Neutrons Neutrons Accidental Background

E StatusJanuary 4, 2006 Hall A Collaboration Meeting QE Event selection: Neutrons Accidental Background

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Rough Q 2 = 1.8 GeV 2 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 N 2 proton mis-ID

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Projected Results Systematic uncertainties for highest Q 2 point still smaller than shown statistical uncertainty. Projected error bars assume results match the Galster parameterization.

E StatusJanuary 4, 2006 Hall A Collaboration Meeting The Future: G E 4.5 GeV 2 ? E 0 =3.7 GeV/c, E=1.3 GeV/c, θ BB =59° to measure G E n /G M 4.5 GeV 2 (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 I b to 24uA L en ~ /(s cm 2 ). A measurement with the 20% relative statistical uncertainty (vs. 14% at 3.4 GeV 2 ) could be done in 500hrs (25 days).

E StatusJanuary 4, 2006 Hall A Collaboration Meeting 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 G E n. Presently analyzing the 1.8 GeV 2 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 GeV 2 analysis this spring, and results from all datasets by late 2007/early 2008 (my estimate). Investigating measurement at 4.5 GeV 2 ?

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Backup slides

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Proton Asymmetry

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Background Asymmetry

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Data Quality The experiment ran for 3 months in Spring Four datasets (Q 2 =1.4, 1.8, 2.4, 3.4 GeV 2 ) 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. Beam polarization ~84% (Q 2 ~3.5 GeV runs) Target polarization ~50% IN BEAM

E StatusJanuary 4, 2006 Hall A Collaboration Meeting World data on G E n

E StatusJanuary 4, 2006 Hall A Collaboration Meeting Data Analysis Results shown are from an advanced preliminary analysis of the 1.8 GeV 2 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) 3 He(e, e N)