Lead (208Pb) Radius Experiment : PREXE = 1 GeV, 05Elastic Scattering Parity-Violating Asymmetry

PREX : density -dependence of the symmetry energy. Nuclear physics community very interested in this !

Z0 : Clean Probe Couples Mainly to Neutrons

Nuclear Theory

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FN (Q2)

( Dany Page )

ppm5.0

Obtained 20% statistics

Main problem: radiation degradation of vacuum seals and HRS controls systems

Applications : Nuclear Physics, Neutron Stars , Atomic Parity, Heavy Ion

CollisionsRan 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• <Q2> : low-current cavity monitors, GEM detectors

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“slug” ~ 1 day

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

(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.

Kiad’s HAPLOG 2450: We were underbending by 5 mrad, need to run 760 A septum (was 729 A) Non-optimal Q2

Problem: Missing acceptance. Q2 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 septum @ 775 A

Ebeam = 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 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).

dRN/R N = 1 %