1. E12-07-108: (GMp) Precision Measurement of the Proton Elastic Cross Section at High Q 2 Vincent Sulkosky Massachusetts Institute of Technology for the E12-07-108 Collaboration Spokespeople: J. Arrington, E. Christy, S. Gilad, B. Moffit, V. Sulkosky, B. Wojtsekhowski Hall A Collaboration Meeting December 10 th, 2012

2. Introduction

3. Goals for GMp  Accurately measure e-p elastic cross section in kinematics similar to other JLab form factor measurements  Improve accuracy of the cross section by as much as a factor of 4 (< 2%) over previous measurements  Key input to all form factors and many of other experiments, where elastic scattering is a background  Provide measurement of power scaling for GMp in the range Q 2 = 7-14 GeV 2  Approved for 24 PAC days

4. Kinematics

5. PAC Approved 24 days

6. Control of Systematics Planned improvements  Tracking efficiency  Include front chambers of FPP as third wire chamber with VDCs  Target density  Use precise optics to provide software cuts on vertex  Use race-track cell targets with vertical flow to minimize fluctuations  Solid Angle  A benefit of improved optics  Precise determination of target location using swing arm

7. HRS Detector Stacks Use standard detectors including one plane of FPP for additional tracking

8. ~ 100 wires need to be restrung FPP (front chambers) Problems: gas consumption > 50 l/h HV trips often due to gas, many dead wires/some electronics Done: repair of dead electronics built parallel gas distribution tests of each wire/disconnect dead Still to do: HV distribution in one layer; gas distribution should be as wide as a straw block; tension test for each wire

9. VDC Improvements  Upgrade electronics to use 1877S, which allows sparsification  Replace aging A/D cards and will reuse MAD cards  Provide very good stability against oscillations and rate capability of 8 MHz (in full chamber)

10. Gas Cherenkov Improvements  Reflectivity measurements of HRS GCC mirrors will begin this month  After initial measurements, recoating of mirrors  Check and replace PMTs as needed  Cosmic mirror calibration

11. Target Configuration LH 2 : 15 cm Racetrack:  Vertical flow design  Dedicated studies of density  Luminosity monitors in datastream Solid Al Foils (Dummy): Endcap subtraction Carbon Optics Targets: 1-2 cm spacing along z vertex for extended target acceptance Solid targets/Endcaps measured with x-ray attenuation

12. HRS Optics and Angle Wire target on strong arm, reproducibility of 100 microns sufficient, 20 microns is likely achievable

13. Expected Precision

14. Systematic Uncertainties

16. Tasks & Responsibilities Tasks Commitments Scattering chamber designJLAB – A. Gavalya Strong arm wire target for HRSHall A – J. Miller HRS preparations – VDC, FPPHall A – 1.5 FTE Analysis softwareJLAB – A. Camsonne, O. Hansen LH 2 TargetJLAB – D. Meekins, J-P Chen Beam lineHall A – D. Higinbotham, B. Michaels Refurbish Gas Č counter ( recoat mirrors, replace PMTs) MIT – V. Sulkosky Shower summers for trigger and NIM trigger electronics YerPHI – A. Shahinyan, Hall A – B. Wojtsekhowski S0 mounting on the GCHall A – B. Wojtsekhowski, FIU –P. Khetarpal (FIU) Commissioning Run PlanHU – E. Christy

17. Tasks Commitments Simulations for absolute x-sections (tracking, acceptances, optics, background) Sieve-slit and collimators Shifts (long run!) Data analysis Tasks & Responsibilities (cont.)

18. Commitments in Manpower  FPP work: Albert Shahinyan, Galust Sargsyan and Karen (YerPHI)  HRS detectors:  Milan Dukic (NCCU technician) for three weeks  Hamza Atac (Temple) for two weeks  NSU student for one month  Longwu Ou (MIT student) for one month  Kai Pan (UVa student) for two weeks  Puneet Khetarpal (FIU postdoc) for two weeks  John LeRose (JLab) part time  Mohamed Nuh Hashir Rashad (ODU); DVCS graduate student  JinJin Pan (HU); graduate student (potential GMp student)  Yang Wang (WM); graduate student (potential GMp student)

19. Potential Physics Prospects

20. Summary  First experiment to run in the 12-GeV era with DVCS.  GMp will provide a baseline for the 21 st century level of accuracy in form factor measurements by precisely measuring the cross section at Q 2 up to 14 GeV 2.  It is the only measurement of the cross section; key input to all form factors and many of other experiments  The DVCS luminosity × HRS-R solid angle (1/8 of GMp proposal) and restricted angle range of HRS-R allows for some parallel running of GMp during DVCS data taking.  Collaborators are welcome to participate; much work is required before 2014.