1. E12-09-019 Precision Measurement of the Neutron Magnetic Form Factor up to Q 2 =13.5 (GeV/c) 2 by the Ratio Method B. Quinn, J. Annand, R. Gilman, B. Wojtsekhowski Hall A collab Approved by PAC 34 (except Q 2 =16 and 18 (GeV/c) 2 points) PAC 35 allocated 25 of requested 31 days. B.Quinn Carnegie Mellon Univ. Hall A collab. mtg. Dec. 15/11 1

2. 2 Introduction Elastic scattering from spin ½ target (one photon exchange approx.) where: Among the simplest, most fundamental of hadronic observables Helps provide definitive test of nucleon structure theory ( With proton form factor, gives access to isovector form factor, which is ‘easy’ case for l QCD.) Sets sum rule for GPD measurements/predictions B. Quinn Carnegie Mellon Univ.

3. 3 Technique Ratio Method: Measure quasi-elastic scattering from deuteron tagged by coincident nucleon: d(e,e’p) and d(e,e’n) Many systematic effects (experimental and theory) cancel in ratio. Expect very small correction for Electric because small form factor and large kinematic weighting of Magnetic B. Quinn Carnegie Mellon Univ.

4. 4 HCal replaces BIG-Hand for nucleon detection BIG Bite instrumented with GEMS for higher luminosity B. Quinn Carnegie Mellon Univ.

5. 5 Systematics Ratio Method is insensitive to: Target thickness Target density Beam current Beam structure Live time (electron) trigger efficiency Electron track reconstruction Electron acceptance Important to understand: Neutron efficiency/proton efficiency  HCal almost ideal Neutron acceptance/proton acceptance B. Quinn Carnegie Mellon Univ.

6. 6 Apparatus BigBite Spectrometer Instrumented with: -GEM planes from SBS -Electromagnetic Cal. -Gas Cerenkov -timing planes Allows high luminosity B. Quinn Carnegie Mellon Univ.

7. 7 Apparatus (2) Hadron Calorimeter (HCal) to be built for Super BigBite Spectrometer (SBS) provides ideal replacement for BigHAND stack Iron/scintillator sampling calorimeter 11X22 identical modules High energy-deposition - High threshold - High Luminosity Excellent spatial resolution - Tight cut on nucleon direction (wrt q-vector) High efficiency for n and p - Nearly equal (cancel in ratio) Iron Scintillator B. Quinn Carnegie Mellon Univ.

8. 8 Apparatus (3) Results from Geant4 Simulation (matches published results for COMPASS calorimeter). Assume identical modules, 3X3 cluster size for hits With fast scint./WLS (5X5 cluster) B. Quinn Carnegie Mellon Univ.

9. Apparatus (4) 9B. Quinn Carnegie Mellon Univ.

10. HRS used for neutron calibration via 10B. Quinn Carnegie Mellon Univ.

11. 11 Simulation Quasi-elastic On shell spectator(  Struck nucleon off shell) Boost to struck nucleon rest frame Isotropic distribution -Weighted by cross section (using Bodek parameterization) Boost back to lab Fold in resolution, make (weighted) increment of spectra Inelastic GENEV physics Monte Carlo (Genoa/CLAS) On-shell initial nucleons (with Fermi momentum) Boost to struck nucleon rest frame Generate GENEV event (with boosted beam energy) Boost back to lab Fold in resolution, increment (un-weighted) spectra Inelastic normalized empirically to quasi-elastic

12. Hours requested739 Approved600 Fixed overhead214 Fraction of running time74% 12B. Quinn Carnegie Mellon Univ.

13. 13 Projected results B. Quinn Carnegie Mellon Univ.

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17. Introduction Technique Systematics Apparatus Simulation/Projected results 17B. Quinn Carnegie Mellon Univ.