1. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Lead ( 208 Pb) Radius Experiment : PREX E = 1 GeV, Elastic Scattering Parity-Violating Asymmetry PREX : precise measurement of the density -dependence of the symmetry energy. Z 0 : Clean Probe Couples Mainly to Neutrons Fundamental Nuclear Physics Many applications: 1.Nuclear Physics 2.Neutron Stars 3.Atomic Parity Violation 4.Heavy Ion Collisions Combine with astophysics observations Is dense Neutron-rich matter exotic ? F N (Q 2 ) ( Dany Page ) ( T.W. Donnelly, J. Dubach, I Sick )

2. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Mar 1-5 Source Setup Mar 11-24 Sched. Commis. Mar 19 – Apr 6 Actual Commissioning Apr 14 – 23 Pb Production:  PC systematic ! Systematic Studies 12 C, pulsed beam (Angle calibration, adjust HRS tune, Compton, dithering, focal plane detectors) 17 Coul. O-ring repair Target Accident Apr 29 Vacuum Repair Apr 29 – May 11 Pb Production (good) May 11 - 14 Vacuum Repair May 14 – 20 Pb Production May 20 – June 3 Replace all O-rings Leak checks 41 C total June 3 - Now Pb Production End June 20 ~ 65 C total 17 C bad ? 48 C good ? Hall A Meeting PREX Timeline (2010) Proposal : 130 Coulombs Magnet problems

3. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Source Studies Optimizing laser optics to minimize helicity-correlated systematics. Kent Paschke, Gordon Cates, Mark Dalton, Rupesh Silwal Charge Asymmetry Hel. Correl. Diff (X) Hel. Correl. Diff (Y) Hel. Correl. Diff (X) Delta X (um) Delta Y (um) Hel. Correl. Diff (Y) ~ 2000 ppm ~ 0.5 um BPMs in Injector Region Transmission of Helicity-Correlated Position DIffs

4. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB 16 O Hydrogen Water Cell : Measure Nilanga Liyanage, Seamus Riordan, Kiadtisak Saenboonruang, (agrees with survey)

5. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Optics of HRS + New Septum Nilanga Liyanage, Seamus Riordan, Kiadtisak Saenboonruang,

6. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB At 2 uA Cavity Monitors John Musson, Zafar Ahmed 4 mm Resolution ~1 mm at 25 to 50 nA Time axis Magnets used to calibrate How to judge low currents: scintillator

7. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Collimators Septum Magnet Top view target HRS-L Q1 HRS-R Q1 PREX Region After Target O-Rings (which failed)

8. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Collimators inside Q1 Symmetry in all dimensions to 1 mm

9. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Finding HRS Tune Acceptance defined by collimator Efficient overlap with detectors John LeRose, Seamus Riordan, Dustin McNulty, et.al.

10. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Nilanga Liyanage, Seamus Riordan, Kiadtisak Saenboonruang, Alexandre Camsonne, Ole Hansen, Guido Urciuoli, Evaristo Cisbani Plot from Megan Friend New GEM Detectors High-rate tracking (issue for Q 2 ) 4 Chambers on L-HRS are working.

11. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Diamond LEAD Three bays Lead (0.5 mm) sandwiched by diamond (0.15 mm) Liquid He cooling (30 Watts) Lead / Diamond Target

12. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Initial Running After 1 Week Non-stat Noise ! Synching Raster To Reduce Noise due to Target Non-uniformity Flat NOT Flat Gordon Cates, Krishna Kumar, Bill Gunning This eliminated the ….

13. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB integrate wait Beam Current Detector (1 of 4) An instability in Pockel Cell “bleeds” into the itegration gate. It depends on helicity. Pockel Cell Related Systematic Error Want small time constants, and same for detectors and bcm time Response to pulsed beam

14. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Other Issues Establishing few - ppb systematic errors. Measurements of A T Double Wien Filter for Spin Flips New Beam Modulation System Requires off-line analysis Small ! (but not public yet) Useful for Qweak

15. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Online (blinded) Asymmetries excluding, for now, the first 17C of data (PC systematic) Corrected for Sign Flips due to IHWP and Wien Left HRS Right HRS Combined Statistics Expectation 0.51 ppm

16. Hall A Collab. Mtg, 6/ 2010R. Michaels, JLAB Projected Errors Statistical Polarimetry 1.5 % 3 % ProposalProjected / Actual (roughly) 6 to 8 % 1 to 2 % 1 % 0.5 % Other Systematics Total Error Error in R N 0.5 % ? 0.5 % 6.3 to 8.2 % 3.2 to 3.7 % 1.1 to 1.3 % 2.1 to 2.7 % PREx