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Lead ( 208 P b) R adius Ex periment : PREX

Lead ( 208 P b) R adius Ex periment : PREX. Elastic Scattering Parity-Violating Asymmetry. E = 1 GeV ,. Z 0 : Clean Probe Couples Mainly to Neutrons. F N (Q 2 ). Applications : Nuclear Physics , Neutron Stars , Atomic Parity, Heavy Ion Collisions.

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Lead ( 208 P b) R adius Ex periment : PREX

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  1. Lead(208Pb) Radius Experiment:PREX Elastic Scattering Parity-Violating Asymmetry E = 1 GeV, Z0 : Clean Probe Couples Mainly to Neutrons FN (Q2) Applications : Nuclear Physics, Neutron Stars , Atomic Parity, Heavy Ion Collisions Ran Mar 19 – June 20, 2010 ( Dany Page ) Obtained 20% statistics Main problem: radiation degradation of vacuum seals and HRS controls systems Nuclear Theory Accomplishments : • Statistics limited, negligible noise • Pb target ran at 50 uA with last 3 days at 70 uA • Precision Compton and Mollerpolarimetry (1.5%) • Thin quartz detector for high rates (1 GHz) • Septum magnet at high luminosity • <Q2>: low-current cavity monitors, GEM detectors PREX : density -dependence of the symmetry energy. Nuclear physics community very interested in this !

  2. PREX Run-averaged asymmetry placed at “1.0” (approx ppm) for presentation. Physics Asymmetry vs Data Set Good chi-square: data are statistical All data. Sign flips removed (product of Wien flip and IHWP flip) “Blinded” Asymmetry ½ our data; the sign flips with Wien x IHWP flip “slug” ~ 1 day Lessons of PREX Plan to release results at April 2011 APS meeting. Expect dRN / RN ~ 2.5% ( Ultimate goal : 1% ) Proposed new measurements with fixes to vacuum system and shielding • Last 3 days @ 70 uA promising : 125 ppm detector noise • @15 Hz equiv. flip rate • Raster synched to flip rate to reduce noise due to target. • Transverse asymmetry AT < 2 ppm

  3.  Apparatus was assembled correctly at the 1 mm level.

  4. Problem: Missing acceptance. Q2 pushed high Kiad’s HAPLOG 2450: We were underbending by 5 mrad, need to run 760 A septum (was 729 A) Non-optimal Q2

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

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

  7. Future Run of PREX

  8. 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)

  9. PREX: Things to Do / Conclusions dRN/R N = 1 % • 12 GeV run ? Thinking: Oct – Dec 2013 Hall A Commissioning. • Asking for 8 to 10 weeks. Go to PAC in Dec 2011. • 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).

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