Lead 208 Pb Radius Experiment E 850 Me

Lead ( 208 Pb) Radius Experiment : E = 850 Me. V, electrons on lead PREX Elastic Scattering Parity Violating Asymmetry 0 Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T. W. Donnelly, J. Dubach, I Sick ) In PWIA (to illustrate) : 208 Pb w/ Coulomb distortions (C. J. Horowitz) : PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Nuclear Structure: Neutron density is a fundamental observable that remains elusive. Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of n. m. density ratio proton/neutrons • Slope unconstrained by data 208 • Adding R N from Pb will eliminate the dispersion in plot. PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

2 Measurement at one Q is sufficient to measure R N Pins down the symmetry energy (1 parameter) PREX accuracy ( R. J. Furnstahl ) PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX & Neutron Stars ( C. J. Horowitz, J. Piekarweicz ) R N calibrates EOS of Neutron Rich Matter Crust Thickness Explain Glitches in Pulsar Frequency ? Combine PREX R N with Obs. Neutron Star Radii Phase Transition to “Exotic” Core ? Strange star ? Quark Star ? Some Neutron Stars seem too Cold Cooling by neutrino emission (URCA) Crab Pulsar PREX PAC 29 Jan 2006 0. 2 fm URCA probable, else not R. Michaels Jefferson Lab

Neutron EOS and Neutron Star Crust Liquid/Solid Transition Density Liquid FP Solid Fig. from J. M. Lattimer & M. Prakash, Science 304 (2004) 536. PREX PAC 29 Jan 2006 TM 1 • Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase. • Thick skin in Pb low transition density in star. R. Michaels Jefferson Lab

Pb Radius vs Neutron Star Radius • The 208 Pb radius constrains the pressure of neutron matter at subnuclear densities. • The NS radius depends on the pressure at nuclear density and above. • Most interested in density dependence of equation of state (EOS) from a possible phase transition. • Important to have both low density and high density measurements to constrain density dependence of EOS. – If Pb radius is relatively large: EOS at low density is stiff with high P. If NS radius is small than high density EOS soft. – This softening of EOS with density could strongly suggest a transition to an exotic high density phase such as quark matter, strange matter, color superconductor, kaon condensate… PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX Constrains Rapid Direct URCA Cooling of Neutron Stars • Proton fraction Yp for matter in beta equilibrium depends on symmetry energy S(n). • Rn in Pb determines density dependence of S(n). • The larger Rn in Pb the lower the threshold mass for direct URCA cooling. • If Rn-Rp<0. 2 fm all EOS models do not have direct URCA in 1. 4 M¯ stars. • If Rn-Rp>0. 25 fm all models do have URCA in 1. 4 M¯ stars. Rn-Rp in 208 Pb If Yp > red line NS cools quickly via direct URCA reaction n p+e+ PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Atomic Parity Violation • Low Q 2 test of Standard Model • Needs R N to make further progress. Isotope Chain Experiments e. g. Berkeley Yb APV PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Neutron Skin and Heavy – Ion Collisions • Impact on Heavy - Ion physics: constraints and predictions • Imprint of the EOS left in the flow and fragmentation distribution. Danielewicz, Lacey, and Lynch, Science 298 (2002) 1592. PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX Physics Impact Measured Asymmetry Correct for Coulomb Distortions Weak Density at one Q 2 Mean Field & Other Models Small Corrections for Atomic Parity Violation G n E s GE MEC 2 Neutron Density at one Q Assume Surface Thickness Good to 25% (MFT) Heavy Ions Neutron Stars Rn PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX: Experimental Issues Spokespersons: P. A. Souder, G. M. Urciuoli, R. Michaels Hall A Collaboration Experiment PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX in Hall A at JLab Spectometers Lead Foil Target Pol. Source Hall A CEBAF PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Optimum Kinematics for Lead Parity: <A> = 0. 5 ppm. E = 850 Me. V, Accuracy in Asy 3% Fig. of merit Min. error in R n maximize: 1 month run 1% in R n PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Beam Asymmetries Araw = Adet - AQ + E+ i xi Slopes from PREX PAC 29 Jan 2006 • natural beam jitter (regression) • beam modulation (dithering) R. Michaels Jefferson Lab

Helicity Correlated Differences: Position, Angle, Energy Scale +/- 10 nm BPM X 1 slug Spectacular results from HAPPEX-H show we can do BPM X 2 PREX. Position Diffs average to ~ 1 nm • Good model for controlling laser systematics at source • Accelerator setup (betatron matching, phase advance) PREX PAC 29 Jan 2006 slug BPM Y 1 slug BPM Y 2 slug “Energy” BPM “slug” = ~1 day running R. Michaels Jefferson Lab

Redundant Position Measurements at the ~1 nm level Y (cavity) X (cavity) nm nm (Helicity – correlated differences averaged over ~1 day) X (stripline) PREX PAC 29 Jan 2006 nm Y (stripline) nm R. Michaels Jefferson Lab

Lead Target 208 Pb Liquid Helium Coolant 12 beam C Diamond Backing: • High Thermal Conductivity • Negligible Systematics m red e rast , m Bea PREX PAC 29 Jan 2006 m 4 x 4 R. Michaels Jefferson Lab

Num. events 208 Pb Elastic Lead Target Tests Data taken Nov 2005 Detector 1 st Excited State (2. 6 Me. V) Num. events Momentum (Me. V) Y (m ) PREX PAC 29 Jan 2006 X d) e coor v i s r e p (dis • Check rates • Backgrounds (HRS is clean) • Sensitivity to beam parameters • Width of asymmetry • HRS resolution • Detector resolution (m) R. Michaels Jefferson Lab

Noise • Need 100 ppm per window pair • Position noise already good enough • New 18 -bit ADCs Will improve BCM noise. • Careful about cable runs, PMTs, grounds. Will improve detector noise. • Plan: Tests with Luminosity Monitor to demonstrate capability. PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Transverse Polarization Part I: Left/Right Asymmetry Transverse Asymmetry Theory est. (Afanasev) Systematic Error for Parity “Error in” Transverse polarization Control HRS-Left-right apparatus asymmetry w/ slow feedback on polarized source solenoids. measure in ~ 1 hr (+ 8 hr setup) HRS-Right Need << correction PREX PAC 29 Jan 2006 syst. err. R. Michaels Jefferson Lab

Transverse Polarization Part II: Up/Down Asymmetry Vertical misalignment Systematic Error for Parity Horizontal polarization e. g. from (g-2) • Measured in situ using 2 -piece detector. • Study alignment with tracking & M. C. up/down misalignment • Wien angle feedback ( ) Need HRS-Left HRS-Right << ( Note, beam width is very tiny PREX PAC 29 Jan 2006 ) R. Michaels Jefferson Lab

Warm Septum Existing superconducting septum won’t work at high L Warm low energy (1 Ge. V) magnet designed. Grant proposal in preparation (~100 k$) [Syracuse / Smith College] TOSCA design P resolution ok PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Polarimetry Møller : d. Pe/Pe ~ 3 % PREX: Compton 2 % required (limit: foil polarization) (a high field target ala Hall C being considered) 2 analyses based on either electron or photon detection : 2% syst. at present 1 % desirable Electron only Photon only Superlattice: Pe=86% ! PREX PAC 29 Jan 2006 Preliminary: 2. 5% syst (g only) R. Michaels Jefferson Lab

Upgrade of Compton Polarimeter (Nanda, Lhuillier) in ~ 1. 5 years ron t c e l e s To reach 1% accuracy: • Green Laser (increased sensitivity at low E) laser on-hand, being tested • Integrating Method (removes some systematics of analyzing power) developed during HAPPEX & in 2006 • New Photon Detector PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

PREX : Summary • Fundamental Nuclear Physics with many applications • HAPPEX & test runs have demonstrated technical aspects • Polarimetry Upgrade needed • Beam Time Request Unchanged (30 days) PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab

Corrections to the Asymmetry are Mostly Negligible • Coulomb Distortions ~20% = the biggest correction. • Transverse Asymmetry (to be measured) • Strangeness • Electric Form Factor of Neutron • Parity Admixtures • Dispersion Corrections • Meson Exchange Currents • Shape Dependence Horowitz, et. al. PRC 63 025501 • Isospin Corrections • Radiative Corrections • Excited States • Target Impurities PREX PAC 29 Jan 2006 R. Michaels Jefferson Lab