1. R. Michaels, Jlab Seminar, Apr 27, 2011 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 Ran March – June 2010 in Hall A Graduate Students Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse) Jon Wexler (UMass) Kiadtisak Saenboonruang (UVa) First Results from

2. R. Michaels, Jlab Seminar, Apr 27, 2011 Standard Electroweak Model Gauge bosons Left –handed fermion fields (quarks and leptons) = doublets under SU(2) Right-handed fields = singlets under SU(2) Also 3 fermion families + single complex Higgs doublet Spontaneous symmetry breaking of the Lagrangian. Symmetries Lagrangian i = 1,2,3 and Parity Violation

3. R. Michaels, Jlab Seminar, Apr 27, 2011 A piece of the weak interaction violates parity (mirror symmetry) which allows to isolate it. Negative longitudinal spin Positive longitudinal spin Pb 208 P S (spin) (momentum) Incident electron Target

4. R. Michaels, Jlab Seminar, Apr 27, 2011 Parity Violating Asymmetry + 2 Applications of PV at Jefferson Lab Nucleon Structure (strangeness) -- HAPPEX / G0 Standard Model Tests -- Qweak, Moller Nuclear Structure (neutron density) : PREX Applications of PV at Jefferson Lab

5. R. Michaels, Jlab Seminar, Apr 27, 2011 Idea behind PREX Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick 1989 ) 0 In PWIA (to illustrate) : w/ Coulomb distortions (C. J. Horowitz) : 5

6. R. Michaels, Jlab Seminar, Apr 27, 2011 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

7. R. Michaels, Jlab Seminar, Apr 27, 2011 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 ?

8. R. Michaels, Jlab Seminar, Apr 27, 2011 Reminder: Electromagnetic Scattering determines Pb 208 (charge distribution) 123

9. R. Michaels, Jlab Seminar, Apr 27, 2011 Z of weak interaction : sees the neutrons proton neutron Electric charge 1 0 Weak charge 0.08 1 0 Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies 10

10. R. Michaels, Jlab Seminar, Apr 27, 2011 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.

11. R. Michaels, Jlab Seminar, Apr 27, 2011 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

12. R. Michaels, Jlab Seminar, Apr 27, 2011 ( R.J. Furnstahl ) Measurement at one Q is sufficient to measure R 2 N proposed error Why only one parameter ? (next slide…) PREX:

13. R. Michaels, Jlab Seminar, Apr 27, 2011 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

14. R. Michaels, Jlab Seminar, Apr 27, 2011 Skx-s15 Thanks, Alex Brown PREX Workshop 2008 E/N

15. R. Michaels, Jlab Seminar, Apr 27, 2011 Skx-s20 Thanks, Alex Brown PREX Workshop 2008

16. R. Michaels, Jlab Seminar, Apr 27, 2011 Skx-s25 Thanks, Alex Brown PREX Workshop 2008

17. R. Michaels, Jlab Seminar, Apr 27, 2011 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 17

18. R. Michaels, Jlab Seminar, Apr 27, 2011 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 :

19. R. Michaels, Jlab Seminar, Apr 27, 2011 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 19

20. R. Michaels, Jlab Seminar, Apr 27, 2011 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 ?

21. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX: The entire lab is the experiment CEBAF Hall A Pol. Source Lead Foil Target Spectometers 21

22. R. Michaels, Jlab Seminar, Apr 27, 2011 Hall A at Jefferson Lab Polarized e - Source Hall A

23. R. Michaels, Jlab Seminar, Apr 27, 2011 How to do a Parity Experiment Flux Integration Technique: HAPPEX: 2 MHz PREX: 500 MHz (integrating method) Example : HAPPEX

24. R. Michaels, Jlab Seminar, Apr 27, 2011 Pull Plot (example) PREX Data

25. R. Michaels, Jlab Seminar, Apr 27, 2011 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

26. R. Michaels, Jlab Seminar, Apr 27, 2011 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 :

27. R. Michaels, Jlab Seminar, Apr 27, 2011 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 ~ 2 hours 27

28. R. Michaels, Jlab Seminar, Apr 27, 2011 Methods to Reduce Systematics Voltage change of 58 Volts, added to both the + and - voltages, would zero the asymmetry. A rotatable /2 waveplate downstream of the P.C. allows arbitrary orientation of DoLP A simplified picture: asymmetry=0 corresponds to minimized DoLP at analyzer Perfect DoCP Scanning the Pockels Cell voltage = scanning the retardation phase = scanning residual DoLP Intensity Asymmetry (ppm) Pockels cell voltage offset (V)

29. R. Michaels, Jlab Seminar, Apr 27, 2011 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) Joe Grames, et. al.

30. R. Michaels, Jlab Seminar, Apr 27, 2011 Spin Flipper Joe Grames et.al. V-Wien = +90° MFG1I04A = -45° or +45° MFG1I04B = -45° or +45°

31. R. Michaels, Jlab Seminar, Apr 27, 2011 PAVI 09 Beam Asymmetries A raw = A det - A Q + E + i x i natural beam jitter (regression) beam modulation (dithering) Slopes from 31

32. R. Michaels, Jlab Seminar, Apr 27, 2011 Charge Asymmetry 0.087 +/- 0.151 ppm Slug # ( ~ 1 day) ppm

33. R. Michaels, Jlab Seminar, Apr 27, 2011 Slug # ( ~ 1 day) Units: microns Parity Quality Beam ! Helicity – Correlated Position Differences < ~ 3 nm Wien Flips helped ! Average with signs = what expt feels Points: Not sign corrected

34. R. Michaels, Jlab Seminar, Apr 27, 2011 Detector slopes measured during run A raw = A det - A Q + E + i x i

35. R. Michaels, Jlab Seminar, Apr 27, 2011 Hall A Compton Upgrade with Green Laser Sirish Nanda, et. al. 1 % Polarimetry at 1 GeV

36. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Compton Polarimeter Results

37. R. Michaels, Jlab Seminar, Apr 27, 2011 Hall A Moller Upgrade Superconducting Magnet from Hall C Saturated Iron Foil Targets 1 % Polarimetry Magnet and Target DAQ Upgrade (FADC) Sasha Glamazdin, et.al.

38. R. Michaels, Jlab Seminar, Apr 27, 2011 Moller Results Example : Comparing old and new DAQ Thanks, Zafar Ahmed 38

39. R. Michaels, Jlab Seminar, Apr 27, 2011 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

40. R. Michaels, Jlab Seminar, Apr 27, 2011 Septum Magnet target HRS-L HRS-R collimator 5 0 Septum magnet augments the High Resolution Spectrometers Increased Figure of Merit collimator

41. R. Michaels, Jlab Seminar, Apr 27, 2011 Collimators inside Q1 Symmetry in all dimensions to 1 mm

42. R. Michaels, Jlab Seminar, Apr 27, 2011 Collimators Septum Magnet Top view target HRS-L Q1 HRS-R Q1 PREX Region After Target O-Rings which failed and caused significant time loss

43. R. Michaels, Jlab Seminar, Apr 27, 2011 Water Cell : Measure Nilanga Liyanage, Seamus Riordan, Kiadtisak Saenboonruang (agrees with survey)

44. R. Michaels, Jlab Seminar, Apr 27, 2011 PAVI 09 Q 2 Measurements Use constructed position at target for precise correction of beam position 44

45. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Integrating Detectors DETECTORS UMass / Smith Detector Package in HRS

46. R. Michaels, Jlab Seminar, Apr 27, 2011 High Resolution Spectrometers Momentum (GeV/c) 4.4 MeV 12 C

47. R. Michaels, Jlab Seminar, Apr 27, 2011 Pure, Thin 208 Pb Target Momentum (GeV/c) Lead 5- State 2.6 MeV

48. R. Michaels, Jlab Seminar, Apr 27, 2011 Detector integrates the elastic peak. Backgrounds from inelastics are suppressed. Momentum (GeV/c)

49. R. Michaels, Jlab Seminar, Apr 27, 2011 Backgrounds that might re-scatter into the detector ? Run magnets down: measure inelastic region Run magnets up : measure probability to rescatter No inelastics observed on top of radiative tail. Small systematic for tail. Detector cutoff

50. R. Michaels, Jlab Seminar, Apr 27, 2011 Diamond LEAD Three bays Lead (0.5 mm) sandwiched by diamond (0.15 mm) Liquid He cooling (30 Watts) Lead / Diamond Target 50

51. R. Michaels, Jlab Seminar, Apr 27, 2011 Initial Running After ~ 5 days Non-stat Noise ! Synching Raster Eliminated Noise due to Target Non-uniformity Flat NOT Flat This eliminated the ….

52. R. Michaels, Jlab Seminar, Apr 27, 2011 PAVI 09 Target Density Intact Melted Failure happens fairly suddenly after ~1 week Y Y X X 52

53. R. Michaels, Jlab Seminar, Apr 27, 2011 PAVI 09 Better Best Target thickness vs run # Thick diamond target degraded the least 0 +/- 1% 4.5 %5.6 % 8 % Melts

54. R. Michaels, Jlab Seminar, Apr 27, 2011 integrate wait Beam Current Detector (1 of 4) An instability in Pockel Cell bleeds into the itegration gate. Depends on helicity. Pockel Cell Error : Affected 1 st week (discarded data) Want small time constants, and same for detectors and bcm time Response to pulsed beam

55. R. Michaels, Jlab Seminar, Apr 27, 2011 y z x + - A T > 0 means Beam-Normal Asymmetry in elastic electron scattering i.e. spin transverse to scattering plane Possible systematic if small transverse spin component New results PREX Small A T for 208 Pb is a big (but pleasant) surprise. A T for 12 C qualitatively consistent with 4 He and available calculations (1) Afanasev ; (2) Gorchtein & Horowitz Still very preliminary

56. R. Michaels, Jlab Seminar, Apr 27, 2011 Error SourceAbsolute (ppm)Relative ( % ) Polarization (1) 0.00711.1 Beam Asymmetries (2) 0.00721.1 Detector Linearity0.00711.1 BCM Linearity0.00100.2 Rescattering0.00010 Transverse Polarization0.00120.2 Q 2 (1) 0.00280.4 Target Thickness0.00050.1 12 C Asymmetry (2) 0.00250.4 Inelastic States00 TOTAL0.01302.0 Systematic Errors (1) Normalization Correction applied (2) Nonzero correction (the rest assumed zero)

57. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Physics Result ppm at Q 2 = 0.00906 GeV 2 Statistics limited ( 9% ) Systematic error goal achieved ! (2%) 9.2 % 2.0 %

58. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Asymmetry (P e x A) ppm Slug ~ 1 day (blinded, raw)

59. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Physics Interpretation

60. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX Errors in the asymmetry Absolute (ppm) Relative (%) Polarization 0.007 1.1% Detector Linearity 0.007 1.1% BCM Linearity 0.007 1.1% Re-scattering 0 0 Transverse Polarization 0.001 0.2% Q 2 0.002 0.4% Target Thickness 0.001 0.2% Asymmetry 12 C 0.003 0.5% Inelastics 0 0 TOTAL SYSTEMATIC 0.012 2.1% STATISTICAL ERROR 0.051 9.0% Asymmetry leads to R N ( theory curve, not integrated over acceptance ) Neutron Skin = R N - R P = 0.34 + 0.15 - 0.17 fm arXiv:1010.3246 [nucl-th] Shufang Ban, C.J. Horowitz, R. Michaels Preliminary estimate from C.J. Horowitz 60

61. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX – II Proposal Future ?

62. R. Michaels, Jlab Seminar, Apr 27, 2011 Future ?

63. R. Michaels, Jlab Seminar, Apr 27, 2011 Other Nuclei ? Shape Dependence ? RNRN RNRN Surface thickness arXiv:1010.3246 [nucl-th] Parity Violating Electron Scattering Measurements of Neutron Densities Shufang Ban, C.J. Horowitz, R. Michaels

64. R. Michaels, Jlab Seminar, Apr 27, 2011 PREX : Summary Fundamental Nuclear Physics with many applications Achieved a 9% stat. error in Asymmetry (original goal : 3 %) Systematic Error Goals Achieved !! Significant time-losses due to O-Ring problem and radiation damage Proposal for PREX-II in preparation

65. R. Michaels, Jlab Seminar, Apr 27, 2011 Extra Slides

66. R. Michaels, Jlab Seminar, Apr 27, 2011 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

67. R. Michaels, Jlab Seminar, Apr 27, 2011 Lead Target PAVI 09 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)

68. R. Michaels, Jlab Seminar, Apr 27, 2011 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)

69. R. Michaels, Jlab Seminar, Apr 27, 2011 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

70. R. Michaels, Jlab Seminar, Apr 27, 2011 Luminosity Monitor A source of extremely high rate Established noise floor of 50 ppm

71. R. Michaels, Jlab Seminar, Apr 27, 2011 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… PAVI 09 (slide from C. Horowitz)

72. R. Michaels, Jlab Seminar, Apr 27, 2011 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. PAVI 09 FP TM1 Solid Liquid Neutron Star Crust vs Pb Neutron Skin 208 Pb Neutron Star C.J. Horowitz, J. Piekarawicz

73. R. Michaels, Jlab Seminar, Apr 27, 2011 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, its the density dependence of a 4 that we pin down.

74. R. Michaels, Jlab Seminar, Apr 27, 2011 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. PAVI 09 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)

75. R. Michaels, Jlab Seminar, Apr 27, 2011 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

76. R. Michaels, Jlab Seminar, Apr 27, 2011 PAVI 09 Optimization for Barium -- of possible direct use for Atomic PV 1 GeV optimum