1. R. Michaels PREX at PAVI 09 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry Spokespersons Paul Souder Krishna Kumar Guido Urciuoli Robert Michaels Run in March 2010 !

2. R. Michaels PREX at PAVI 09 Idea behind 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) :

3. R. Michaels PREX at PAVI 09 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 Output Slide adapted from C. Horowitz

4. R. Michaels PREX at PAVI 09 Fundamental Nuclear Physics : What is the size of a nucleus ? Neutrons are thought to determine the size of heavy nuclei like 208 Pb. Can theory predict it ?

5. R. Michaels PREX at PAVI 09 Reminder: Electromagnetic Scattering determines Pb 208 (charge distribution) 123

6. R. Michaels PREX at PAVI 09 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

7. R. Michaels PREX at PAVI 09 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

8. R. Michaels PREX at PAVI 09 ( R.J. Furnstahl ) Measurement at one Q is sufficient to measure R 2 N proposed error * Why only one parameter ? (next slide…) PREX: * 2/3 this error if 100 uA, dP e /P e = 1%

9. R. Michaels PREX at PAVI 09 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 Slide adapted from J. Piekarewicz

10. R. Michaels PREX at PAVI 09 Skx-s15 Thanks, Alex Brown PREX Workshop 2008 E/N

11. R. Michaels PREX at PAVI 09 Skx-s20 Thanks, Alex Brown PREX Workshop 2008

12. R. Michaels PREX at PAVI 09 Skx-s25 Thanks, Alex Brown PREX Workshop 2008

13. R. Michaels PREX at PAVI 09 Interpretation of PREX Acceptance

14. R. Michaels PREX at PAVI 09 Application: Atomic Parity Violation Low Q test of Standard Model Needs R N (or APV measures R N ) 2 APV Isotope Chain Experiments e.g. Berkeley Yb

15. R. Michaels PREX at PAVI 09 Neutron Stars What is the nature of extremely dense matter ? Do collapsed stars form “exotic” phases of matter ? (strange stars, quark stars) Crab Nebula (X-ray, visible, radio, infrared) Application :

16. R. Michaels PREX at PAVI 09 Fig from: Dany Page. J.M. Lattimer & M. Prakash, Science 304 (2004) 536. Inputs: Eq. of state (EOS) Hydrostatics (Gen. Rel.) Astrophysics Observations Luminosity L Temp. T Mass M from pulsar timing PREX helps here (with corrections … ) Mass - Radius relationship pressure density

17. R. Michaels PREX at PAVI 09 PREX & Neutron Stars Crab Pulsar ( C.J. Horowitz, J. Piekarewicz ) 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 ?

18. R. Michaels PREX at PAVI 09 PREX Design CEBAF Hall A Pol. Source Lead Foil Target Spectometers

19. R. Michaels PREX at PAVI 09 Hall A at Jefferson Lab Polarized e - Source Hall A

20. R. Michaels PREX at PAVI 09 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

21. R. Michaels PREX at PAVI 09 Septum Magnet target HRS-L HRS-R collimator 5 0 Septum magnet augments the High Resolution Spectrometers Increased Figure of Merit collimator L / R HRS control vertical A_T. What about horizontal ?

22. R. Michaels PREX at PAVI 09 Collimator at entrance to spectrometer Be degrader Insertable blocker to block Be Aligned in spectrometers to define identical Left / Right scattering angles as well as good up / down symmetry A_T hole  Suppressing A_T systematics Paul Souder

23. R. Michaels PREX at PAVI 09 Events from A_T hole (Be plug) Main detector A_T detector Measures horizontal A_T systematic. (Vertical is measured from Left/Right spectrometers) Thanks: Dustin McNulty Krishna Kumar Paul Souder

24. R. Michaels PREX at PAVI 09 Measure θ from Nuclear Recoil Recoil is large for H, small for nuclei δE=Energy loss E=Beam energy M A =Nuclear mass θ=Scattering angle (3X better accuracy than survey) Scattered Electron Energy (GeV)

25. R. Michaels PREX at PAVI 09 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 : See talk by Gordon Cates

26. R. Michaels PREX at PAVI 09 Two Wien Spin Manipulators in series Solenoid rotates spin +/-90 degrees (spin rotation as B but focus as B 2 ). Flips spin without moving the beam ! Double Wien Filter Crossed E & B fields to rotate the spin Electron Beam SPIN (NEW for PREX) See talk by Riad Suleiman

27. R. Michaels PREX at PAVI 09 Beam Asymmetries A raw = A det - A Q +  E +  i  x i natural beam jitter (regression) beam modulation (dithering) Slopes from

28. R. Michaels PREX at PAVI 09 * The mistake: Helicity signal deflecting the beam through electronics “pickup” Helicity signal to driver reversed Helicity signal to driver removed X Angle BPM Raw ALL Asymetry micron ppm The Corrections Work ! Shown : period of data during HAPPEX ( 4 He) when beam had a helicity-correlated position due to a mistake * in electronics. Helicity-corr. Position diff With corrections

29. R. Michaels PREX at PAVI 09 Final Beam Position Corrections (HAPPEX-H) 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.

30. R. Michaels PREX at PAVI 09 X (cavity) nm Y (cavity) nm X (stripline) nmY (stripline) nm (ii) Resonant microwave cavities (Helicity – correlated differences averaged over ~1 day) HAPPEX 2005 Redundant position measurements at the ~1 nm level (i) Stripline monitors (2 pairs of wires)

31. R. Michaels PREX at PAVI 09 PREX Integrating Detectors DETECTORS UMass / Smith

32. R. Michaels PREX at PAVI 09 Lead Target Liquid Helium Coolant Pb C 208 12 Diamond Backing: High Thermal Conductivity Negligible Systematics Beam, rastered 4 x 4 mm beam (2 x I in proposal)

33. R. Michaels PREX at PAVI 09 Target Assembly

34. R. Michaels PREX at PAVI 09 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 Low Rate at E = 1.1 GeV

35. R. Michaels PREX at PAVI 09 Noise (integrating at 30 Hz) PREX: ~120 ppm Want only counting statistics noise, all others << 120 ppm New 18-bit ADCs  improve beam noise. Careful about cable runs, PMTs, grounds loops.. Test: Use the “Luminosity Monitor” to demonstrate noise (next slide) (HAPPEX data)

36. R. Michaels PREX at PAVI 09 Luminosity Monitor A source of extremely high rate  Established noise floor of 50 ppm

37. R. Michaels PREX at PAVI 09 PREX : Summary Fundamental Nuclear Physics with many applications HAPPEX & test runs have demonstrated technical aspects Polarimetry Upgrade critical 2 month run starting March 2010

38. R. Michaels PREX at PAVI 09 Extra Slides

39. R. Michaels PREX at PAVI 09 “What if ’’ Scenarios dP e /P e = 1% dP e /P e = 2% 50 uA 30 days dR N /R N  1 % 1.2 % 100 uA 60 days dR N /R N -  0.6 % 0.8 % Assuming other systematics are negligible

40. R. Michaels PREX at PAVI 09 Optimum Kinematics for Lead Parity: E = 1 GeV if = 0.5 ppm. Accuracy in Asy 3% n Fig. of merit Min. error in R maximize: 1 month run 1% in R n (2 months x 100 uA  0.5% if no systematics) 5

41. R. Michaels PREX at PAVI 09 Polarimetry Accuracy : 1% from 2 methods Hydrogen: 86.7% ± 2%Helium: 84.0% ± 2.5% HAPPEX Compton Polarimety Measuremens Møller (New High-field design ) Compton

42. R. Michaels PREX at PAVI 09 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… (slide from C. Horowitz)

43. R. Michaels PREX at PAVI 09 ~ 50 ppm noise per pulse  milestone for electronics Asymmetries in Lumi Monitors after beam noise subtraction Jan 2008 Data ( need << 120 ppm)

44. R. Michaels PREX at PAVI 09 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 Star Crust vs Pb Neutron Skin 208 Pb Neutron Star C.J. Horowitz, J. Piekarawicz

45. R. Michaels PREX at PAVI 09 PREX: pins down the symmetry energy (1 parameter) ( R.J. Furnstahl ) energy cost for unequal # protons & neutrons PREX PREX error bar Pb 208 Actually, it’s the density dependence of a 4 that we pin down.

46. R. Michaels PREX at PAVI 09 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+ (slide from C. Horowitz)

47. R. Michaels PREX at PAVI 09 How to Measure Neutron Distributions, Symmetry Energy Proton-Nucleus Elastic Pion, alpha, d Scattering Pion Photoproduction Heavy ion collisions Rare Isotopes (dripline) Magnetic scattering PREX (weak interaction) Theory MFT fit mostly by data other than neutron densities Involve strong probes Most spins couple to zero.

48. R. Michaels PREX at PAVI 09 Target Spectro: SQQDQ Hall A Cherenkov cones PMT Compton Moller Polarimeters

49. R. Michaels PREX at PAVI 09 Isospin Diffusion (NSCL) Probe the symmetry energy in 124 Sn + 112 Sn Heavy Ions (adapted from Betty Tsang, PREX Workshop)

50. R. Michaels PREX at PAVI 09 At 5 0 the new Optimal FOM is at 1.05 GeV (+/- 0.05) (when accounting for collimating small angle, not shown) 1% @ ~1 GeV

51. R. Michaels PREX at PAVI 09 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

52. R. Michaels PREX at PAVI 09 Good energy resolution Successful Results of beam tests Jan 2008

53. R. Michaels PREX at PAVI 09 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

54. R. Michaels PREX at PAVI 09 Optimization for Barium -- of possible direct use for Atomic PV 1 GeV optimum

55. R. Michaels PREX at PAVI 09 Warm Septum Existing superconducting septum won’t 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