1. R. Michaels PREX at HE06 July 2006 Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick ) 0 In PWIA (to illustrate) : w/ Coulomb distortions (C. J. Horowitz) : 208 208 Pb E = 850 MeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

2. R. Michaels PREX at HE06 July 2006 Parity Violating Asymmetry + 2 Applications of PV at Jefferson Lab Nucleon Structure (strangeness) -- HAPPEX / G0 Standard Model Tests ( ) -- e.g. Qweak Nuclear Structure (neutron density) : PREX Applications of PV at Jefferson Lab

3. R. Michaels PREX at HE06 July 2006 Z of weak interaction : sees the neutrons 0 proton neutron Electric charge 1 0 Weak charge 0.08 1 Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies

4. R. Michaels PREX at HE06 July 2006 Reminder: Electromagnetic Scattering determines Pb 208 (charge distribution) 123

5. R. Michaels PREX at HE06 July 2006 neutron weak charge >> proton weak charge is small, best observed by parity violation Electron - Nucleus Potential electromagnetic axial Neutron form factor Parity Violating Asymmetry Proton form factor Pb is spin 0 208

6. R. Michaels PREX at HE06 July 2006 ( R.J. Furnstahl ) Measurement at one Q is sufficient to measure R 2 N PREX error bar Why only one parameter ? (next slide…) PREX:

7. R. Michaels PREX at HE06 July 2006 PREX: pins down the symmetry energy (1 parameter) ( R.J. Furnstahl ) energy cost for unequal # protons & neutrons PREX PREX error bar Pb 208

8. R. Michaels PREX at HE06 July 2006 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 Adding R from Pb will eliminate the dispersion in plot. N 208

9. R. Michaels PREX at HE06 July 2006 PREX & Neutron Stars Crab Pulsar ( C.J. Horowitz, J. Piekarweicz ) R calibrates EOS of Neutron Rich Matter Combine PREX R with Obs. Neutron Star Radii Some Neutron Stars seem too Cold N N Crust Thickness Explain Glitches in Pulsar Frequency ? Strange star ? Quark Star ? Cooling by neutrino emission (URCA) 0.2 fm URCA probable, else not Phase Transition to Exotic Core ?

10. R. Michaels PREX at HE06 July 2006 FP TM1 Solid Liquid Liquid/Solid Transition Density Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase. Thick skin in Pb low transition density in star. Neutron EOS and Neutron Star Crust Fig. from J.M. Lattimer & M. Prakash, Science 304 (2004) 536. ( C.J. Horowitz, J. Piekarweicz )

11. R. Michaels PREX at HE06 July 2006 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… ( C.J. Horowitz, J. Piekarweicz )

12. R. Michaels PREX at HE06 July 2006 PREX Constrains Rapid Direct URCA Cooling of Neutron Stars Proton fraction Y p for matter in beta equilibrium depends on symmetry energy S(n). R n in Pb determines density dependence of S(n). The larger R n in Pb the lower the threshold mass for direct URCA cooling. If R n -R p <0.2 fm all EOS models do not have direct URCA in 1.4 M ¯ stars. If R n -R p >0.25 fm all models do have URCA in 1.4 M ¯ stars. R n -R p in 208 Pb If Y p > red line NS cools quickly via direct URCA reaction n p+e+ ( C.J. Horowitz, J. Piekarweicz )

13. R. Michaels PREX at HE06 July 2006 Impact on Atomic Parity Violation Low Q test of Standard Model Needs R to make further progress. 2 N APV Isotope Chain Experiments e.g. Berkeley Yb

14. R. Michaels PREX at HE06 July 2006 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 Isospin Corrections Radiative Corrections Excited States Target Impurities Horowitz, et.al. PRC 63 025501

15. R. Michaels PREX at HE06 July 2006 PREX: Experimental Issues Spokespersons: P.A. Souder, G.M. Urciuoli, R. Michaels Hall A Collaboration Experiment

16. R. Michaels PREX at HE06 July 2006 PREX in Hall A at JLab CEBAF Hall A Pol. Source Lead Foil Target Spectometers

17. R. Michaels PREX at HE06 July 2006 Hall A at Jefferson Lab Polarized e - Source Hall A

18. R. Michaels PREX at HE06 July 2006 High Resolution Spectrometers Elastic Inelastic detector Q Dipole Quad Spectrometer Concept: Resolve Elastic target Left-Right symmetry to control transverse polarization systematic 1 st excited state Pb 2.6 MeV

19. R. Michaels PREX at HE06 July 2006 Halfwave plate (retractable, reverses helicity) Laser Pockel Cell flips helicity Gun GaAs Crystal e beam - Rapid, random helicity reversal Electrical isolation from rest of lab Feedback on Intensity Asymmetry Polarized Electron Source

20. R. Michaels PREX at HE06 July 2006 P I T A Effect Laser at Pol. Source Polarization I nduced Transport Asymmetry where Transport Asymmetry Intensity Asymmetry drifts, but slope is ~ stable. Feedback on Important Systematic :

21. R. Michaels PREX at HE06 July 2006 Intensity Feedback Adjustments for small phase shifts to make close to circular polarization Low jitter and high accuracy allows sub-ppm Cumulative charge asymmetry in ~ 1 hour In practice, aim for 0.1 ppm over duration of data-taking. ~ 2 hours HAPPEX

22. R. Michaels PREX at HE06 July 2006 Beam Position Corrections (HAPPEX) X Angle BPM Energy: -0.25 ppb X Target: 1 nm X Angle: 2 nm Y Target : 1 nm Y Angle: <1 nm Beam Asymmetry Results Corrected and Raw, Left spectrometer arm alone, Superimposed! ppm micron Total correction for beam position asymmetry on Left, Right, or ALL detector: 10 ppb Spectacular results from HAPPEX-H show we can do PREX.

23. R. Michaels PREX at HE06 July 2006 Integrating Detection PMT Calorimeter (for lead, fits in palm of hand) ADC Integrator electrons Integrate in 30 msec helicity period. Deadtime free. 18 bit ADC with < 10 nonlinearity. But must separate backgrounds & inelastics ( HRS). - 4

24. R. Michaels PREX at HE06 July 2006 The Raw Asymmetry Flux Integration Technique: HAPPEX: 2 MHz PREX: 850 MHz

25. R. Michaels PREX at HE06 July 2006 Application of Parity Violating Electron Scattering : Isolating the u, d, s quark structure in protons (and He) Electromagnetic Scattering: Parity Violation can Access: HAPPEX & Strange Quarks Hall A Proton Parity Experiment 4

26. R. Michaels PREX at HE06 July 2006 1 H Preliminary 2006 Results Q 2 = 0.1089 ± 0.0011GeV 2 A raw = -1.418 ppm 0.105 ppm (stat) A raw correction ~11 ppb Raw Parity Violating Asymmetry Helicity Window Pair Asymmetry Asymmetry (ppm) Slug

27. R. Michaels PREX at HE06 July 2006 Strange FF near ~0.1 GeV 2 Preliminary G M s = 0.28 +/- 0.20 G E s = -0.006 +/- 0.016 ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of electric distribution

28. R. Michaels PREX at HE06 July 2006 Polarimetry Accuracy : 2 % required, 1% desired Hydrogen: 86.7% ± 2%Helium: 84.0% ± 2.5% Preliminary Prelim. HAPPEX Results Møller : P e /P e ~ 3 % (limit: foil polarization) (a high field target ala Hall C being considered) Compton : 2% syst. at present

29. R. Michaels PREX at HE06 July 2006 Upgrade of Compton Polarimeter 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 electrons

30. R. Michaels PREX at HE06 July 2006 Optimum Kinematics for Lead Parity: E = 850 MeV, = 0.5 ppm. Accuracy in Asy 3% n Fig. of merit Min. error in R maximize: 1 month run 1% in R n

31. R. Michaels PREX at HE06 July 2006 Lead Target Liquid Helium Coolant Pb C 208 12 Diamond Backing: High Thermal Conductivity Negligible Systematics Beam, rastered 4 x 4 mm beam

32. R. Michaels PREX at HE06 July 2006 PREX : Summary Fundamental Nuclear Physics with many applications HAPPEX & test runs have demonstrated technical aspects Polarimetry Upgrade needed Will run 1 month in 2008

33. R. Michaels PREX at HE06 July 2006 Extra Slides

34. R. Michaels PREX at HE06 July 2006 Measured Asymmetry Weak Density at one Q 2 Neutron Density at one Q 2 Correct for Coulomb Distortions Small Corrections for G n E G s E MEC Assume Surface Thickness Good to 25% (MFT) Atomic Parity Violation Mean Field & Other Models Neutron Stars R n PREX Physics Impact Heavy I ons

35. R. Michaels PREX at HE06 July 2006 4 He Preliminary 2006 Results Q 2 = 0.07725 ± 0.0007 GeV 2 A raw = 5.253 ppm 0.191 ppm (stat) Raw Parity Violating Asymmetry Helicity Window Pair Asymmetry A raw correction ~ 0.12 ppm Slug Asymmetry (ppm)

36. R. Michaels PREX at HE06 July 2006 Optimization for Barium -- of possible direct use for Atomic PV 1 GeV optimum

37. R. Michaels PREX at HE06 July 2006 X (dispersive coord) (m) Y (m) Momentum (MeV) Detector Pb Elastic 208 1 st Excited State (2.6 MeV) Lead Target Tests Check rates Backgrounds (HRS is clean) Sensitivity to beam parameters Width of asymmetry HRS resolution Detector resolution Num. events Data taken Nov 2005

38. R. Michaels PREX at HE06 July 2006 Neutron Skin and Heavy – Ion Collisions Danielewicz, Lacey, and Lynch, Science 298 (2002) 1592. Impact on Heavy - Ion physics: constraints and predictions Imprint of the EOS left in the flow and fragmentation distribution.

39. R. Michaels PREX at HE06 July 2006 B. Krusche arXiv:nucl-ex/0509003 Sept 2005 Example : Recent Pion Photoproduction This paper obtains Mean Field Theory PREX accuracy !! Proton – Nucleus Elastic:

40. R. Michaels PREX at HE06 July 2006 Transverse Polarization HRS-LeftHRS-Right Transverse AsymmetrySystematic Error for Parity Error in Left-right apparatus asymmetry Need < measure in ~ 1 hr (+ 8 hr setup) Theory est. (Afanasev) Transverse polarization Part I: Left/Right Asymmetry correctionsyst. err. < Control w/ slow feedback on polarized source solenoids.

41. R. Michaels PREX at HE06 July 2006 Transverse Polarization HRS-LeftHRS-Right Vertical misalignment Systematic Error for Parity Horizontal polarization e.g. from (g-2) Part II: Up/Down Asymmetry ( Note, beam width is very tiny up/down misalignment Measured in situ using 2 -piece detector. Study alignment with tracking & M.C. Wien angle feedback ( ) Need ) <<

42. R. Michaels PREX at HE06 July 2006 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.

43. R. Michaels PREX at HE06 July 2006 Warm Septum Existing superconducting septum wont work at high L Warm low energy (1 GeV) magnet designed. Grant proposal in preparation (~100 k$) [ Syracuse / Smith College] TOSCA design P resolution ok

44. R. Michaels PREX at HE06 July 2006 ( R.J. Furnstahl ) Measurement at one Q is sufficient to measure R 2 N Pins down the symmetry energy (1 parameter) PREX accuracy