1. Spin Asymmetries of the Nucleon Experiment ( E07-003) Anusha Liyanage Hall C Users Meeting January 23, 2010 Measurement Of the Proton Form Factor Ratio at High Q 2 by Using The Double Spin Asymmetries

2. CONTENTS Physics Motivation & HMS Kinematic SANE Layout Analysis Status SIMC Simulation Work Status

3. Dramatic discrepancy ! between Rosenbluth and recoil polarization technique. Physics Motivation & HMS Kinematic For Proton E Beam GeV 4.7255.891 P GeV/C 3.5854.170 Θ (Deg) 22.3022.00 Q 2 (GeV/C) 2 5.1706.259 # of Total runs ~44~135 e-p Events~153~948 RSS (Jlab) Q 2 = 1.5 (GeV/c) 2 M. Jones et al., PRC74 (2006) 035201 GeP-III, Hall C

4. SANE Layout BETA (40°) HMS (14°- 48°) BigCal Lucite Hodoscope Gas Cherenkov Forward Hodoscope B at 80° OR 180° Polarized Target Target Beam position monitor Beam Line e-e- P ΘPΘP ΘeΘe

5. From The Experiment The raw asymmetry, The elastic asymmetry, The beam-target asymmetry, Here, The calculated asymmetry vs μ G E /G M A m = N + - N - N + + N - A P = + Nc A m f P B P T A p = - br Sin Θ *Cos Ф * - aCos Θ * r 2 + c r = G E /G M a, b, c = kinematic factors Θ *, Ф * = pol. and azi. Angles between q and S P B,P T = Beam & Target Pol. f = Dilution Factor Nc = A Correction Term N + = Helicity + Counts N - = Helicity - Counts At Q 2 =6.259 (GeV/C) 2 Θ *≈ 102° and Ф * = 0 From the HMS kinematics, r 2 << c A p = - bSin Θ *Cos Ф * r - aCos Θ * c c P T + = ~71.0%, P T - = ~-65.0%, P B = ~73.0%,

6. Error Propagation From The Experiment….. A p = - bSin Θ *Cos Ф * r - aCos Θ * c c ∆A p = bSin Θ *Cos Ф * ∆r c Using the experiment data at Q 2 =6.259 (GeV/C) 2, ∆r = 0.118 μ ∆r = 2.79 x 0.118 μ ∆r = 0.3 Where, μ – Magnetic Moment of the Proton The error on the μ ∆r from the experimental data with total ep events ~1000, μ ∆r = 0.3

7. Analysis Status HMS Detector Calibration is Completed. Detector Efficiency. Modification of the DC tracking efficiency algorithm is done. (The tracking efficiency is increased by 15%-20%) Extracted the elastic events. Correlation corrections are completed.

8. Tracking Efficiency Corrections Used 4/6 DC hits instead of 5/6 DC hits. Used the tracks which have stubs only on one of the DC’s as good tracks. Tracking Efficiency Vs Run Number Drift Chamber hits Vs x focal plane Ch1 Vs hsxfp Ch2 Vs hsxfp Ch1 Vs hsxfp Ch2 Vs hsxfp

9. Tracking Efficiency Correction Tracking Efficiency Vs x-focal plane Use the Tracking Efficiency as a function of hsxfp to correct data.

10. Extracted the elastic events Momentum Difference, dPel_hms HMSHMS C O IN HMS – abs(dPel_hms ) < 0.02 abs(hsdelta) < 8 hcer_npe < 0.2 hsshtrk/hse > 0.01 COIN - abs(EHMS-eclust+0.37) <1 abs(XHMS-xclust-0.15) < 5 abs(YHMS-yclust+0.41) < 10 dPel_hms = P HMS – P cal P cent Q 2 = 4M 2 E 2 cos 2 Θ M 2 +2ME+E 2 sin 2 Θ ν = Q 2 2M P cal = Sqrt( ν 2 + 2M ν ) Elliptic cut y i = variable a i = offset σ i = cut

11. X/Y position difference X position Difference HMS cuts COIN cuts X/Y_HMS – Predicted X/Y positions (Target Mag. Field Corrected)on the BigCal using the HMS kinematics X/Yclust - Measured X/Y positions on the BigCal X_HMS - Xclust Y position Difference Y_HMS - Yclust HMS cuts COIN cuts Y_HMS - Yclust

12. Correlation Corrections for …. The dPel_hms vs srast_y.... The Y position difference Vs srast _y …. dPel_hms vs srast_y dPe_hms vs srast_y Corrected dPel_hms vs srast_y Ydiff Vs srast_y Corrected Ydiff Vs srast_y

13. SIMC Simulation HMS Single Arm Variables HMS Coincidence with BigCalVariables SIMC Simulation Experimental Data σ = 0.79 σ = 1.69 σ = 2.98 σ = 4.21 σ = 0.0041 σ = 0.0055 SIMC Counts = 1696 Data = 950 Target Magnetic Field is corrected Normalized to Charge, Tracking Efff. and Comp. L.T.

14. Work Status HMS Calibration – completed Preliminary elastic event selection – completed To Do ….. Improve the SIMC simulation Use the Data which are corrected with the new Tracking Efficiency correction function.(with hsxfp) Include the new tracking algorithm to the simulation Use the Efficiency Corrections Extract the Asymmetry and the G E /G M Ratio