Lead ( 208 Pb) Radius Experiment : PREX E = 1 GeV, Elastic Scattering Parity-Violating Asymmetry PREX : density -dependence of the symmetry energy. Nuclear physics community very interested in this ! Z 0 : Clean Probe Couples Mainly to Neutrons Nuclear Theory F N (Q 2 ) ( Dany Page ) Obtained 20% statistics Main problem: radiation degradation of vacuum seals and HRS controls systems Applications : Nuclear Physics, Neutron Stars, Atomic Parity, Heavy Ion Collisions Ran Mar 19 – June 20, 2010 Accomplishments : Statistics limited, negligible noise Pb target ran at 50 uA with last 3 days at 70 uA Precision Compton and Moller polarimetry (1.5%) Thin quartz detector for high rates (1 GHz) Septum magnet at high luminosity : low-current cavity monitors, GEM detectors

Blinded Asymmetry slug ~ 1 day Plan to release results at April 2011 APS meeting. Expect dR N / R N ~ 2.5% ( Ultimate goal : 1% ) Proposed new measurements with fixes to vacuum system and shielding Last 3 70 uA promising : 125 ppm detector Hz equiv. flip rate Raster synched to flip rate to reduce noise due to target. Transverse asymmetry A T < 2 ppm (product of Wien flip and IHWP flip) Good chi-square: data are statistical Lessons of PREX PREX Physics Asymmetry vs Data Set Run-averaged asymmetry placed at 1.0 (approx ppm) for presentation. ½ our data; the sign flips with Wien x IHWP flip All data. Sign flips removed

Apparatus was assembled correctly at the 1 mm level.

Kiads HAPLOG 2450 : We were underbending by 5 mrad, need to run 760 A septum (was 729 A) Non-optimal Q 2 Problem: Missing acceptance. Q 2 pushed high

(thanks, Bogdan W.) R. Michaels, Oct 2010 Need GEANT simulations to design the shielding Need engineering and design support.

Using HAMC (Monte Carlo) to predict a future running point. How good is HAMC ? 1 - HRS Keep apparatus same Run 775 A E beam = 925 to 1000 MeV

Future Run of PREX

Lead / Diamond Target Seem to melt after ~1 week We melted two targets A third ran for 4 days at 70 uA. Strategy ? Run with ~12 targets 6 lead/diamond 6 lead/carbon (carbon more robust)

PREX: Things to Do / Conclusions 12 GeV run ? Thinking: Oct – Dec 2013 Hall A Commissioning. Asking for 8 to 10 weeks. Go to PAC in Dec Assuming approval : In ~12 month period prior to experiment: Re-design beamline to withstand radiation & thermal cycling. Design radiation shielding to protect equipment. Minor mods to targets ( try Pb/carbon, add more targets). dR N /R N = 1 %