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R. Michaels, Jlab PAVI-11 Lead ( 208 Pb) Radius Experiment : PREX E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry Spokespersons Kent Paschke, Paul Souder, Krishna Kumar, Guido Urciuoli, Robert Michaels (presenting) Thomas Jefferson National Accelerator Facility PREX-I Results 2010 Run Approved PREX-II Proposal Future : PREX-N ? (N = III, IV, V …) PAVI – 11 Conference

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R. Michaels, Jlab PAVI-11 Z 0 of weak interaction : sees the neutrons proton neutron Electric charge 1 0 Weak charge Neutron form factor Parity Violating Asymmetry T.W. Donnelly, J. Dubach, I. Sick C.J. Horowitz Nucl. Phys. A 503, 589, 1989 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, , 2001

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R. Michaels, Jlab PAVI-11 Hall A at Jefferson Lab Hall A

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R. Michaels, Jlab PAVI-11 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

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R. Michaels, Jlab PAVI-11 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 5

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R. Michaels, Jlab PAVI-11 Skx-s15 Thanks, Alex Brown PREX Workshop 2008 E/N

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R. Michaels, Jlab PAVI-11 Skx-s20 Thanks, Alex Brown PREX Workshop 2008 E/N

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R. Michaels, Jlab PAVI-11 Skx-s25 Thanks, Alex Brown PREX Workshop 2008 E/N 8

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R. Michaels, Jlab PAVI-11 Application: Atomic Parity Violation Low Q test of Standard Model Needs R N (or APV measures R N ) 2 Isotope Chain Experiments e.g. Berkeley Yb 9 APV

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R. Michaels, Jlab PAVI-11 PREX & Neutron Stars Crab Pulsar C.J. Horowitz, J. Piekarewicz R N calibrates equation of state (pressure vs density) of Neutron Rich Matter Combine PREX R N with Observed Neutron Star Radii Some Neutron Stars seem too cold Strange star ? Quark Star ? Explained by Cooling by neutrino emission (URCA process) ? 0.2 fm URCA probable, else not Phase Transition to Exotic Core ? Fig from: Dany Page. J.M. Lattimer & M. Prakash, Science 304 (2004) 536.

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R. Michaels, Jlab PAVI-11 PREX Overview CEBAF Hall A JLAB Pol. Source Lead Foil Target Spectometers Parity: The entire lab is the experiment

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R. Michaels, Jlab PAVI-11 Slug # ( ~ 1 day) Units: microns Parity Quality Beam ! ( why we love Jlab ! ) Helicity – Correlated Position Differences < ~ 3 nm Average with signs = what expt feels Points: Not sign corrected

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R. Michaels, Jlab PAVI-11 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. 13

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R. Michaels, Jlab PAVI-11 Hall A Compton Upgrade with Green Laser Sirish Nanda, et. al. (Megan Friends talk) 1 % Polarimetry at 1 GeV

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R. Michaels, Jlab PAVI-11 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. (talk Thurs)

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R. Michaels, Jlab PAVI-11 Hall A High Resolution Spectrometers Elastic Inelastic detector Dipole Quads target DETECTOR footprint 2.6 MeV Pure, Thin 208 Pb Target Scattered Electrons Momentum (GeV/c) Resolve Elastic Scattering Discriminate Excited States 16

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R. Michaels, Jlab PAVI-11 Diamond LEAD Three bays Lead (0.5 mm) sandwiched by diamond (0.15 mm) Liquid He cooling (30 Watts) Lead / Diamond Target

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R. Michaels, Jlab PAVI-11 Performance of Lead / Diamond Targets Last 4 days at 70 uA Targets with thin diamond backing (4.5 % background) degraded fastest. Thick diamond (8%) ran well and did not melt at 70 uA. melted NOT melted Solution: Run with 10 targets.

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R. Michaels, Jlab PAVI-11 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 Preliminary ! Publication in preparation 19

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R. Michaels, Jlab PAVI-11 Error SourceAbsolute (ppm) Relative ( % ) Polarization (1) Beam Asymmetries (2) Detector Linearity BCM Linearity Rescattering Transverse Polarization Q 2 (1) Target Thickness C Asymmetry (2) Inelastic States00 TOTAL Systematic Errors (1) Normalization Correction applied (2) Nonzero correction (the rest assumed zero) PREX-I Result Statistics limited ( 9% ) Systematic error goal achieved ! (2%) 20

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R. Michaels, Jlab PAVI-11 PREX Asymmetry (P e x A) ppm Slug ~ 1 day

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R. Michaels, Jlab PAVI-11 Neutron Skin = R N - R P = fm Establishing a neutron skin at ~90 % CL Asymmetry leads to R N fig from C.J. Horowitz PREX data Preliminary: Awaiting the final acceptance function: * *

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R. Michaels, Jlab PAVI-11 PREX-I Result, cont. theory: P. Ring Atomic Number, A r N - r P (fm) DATA A physics letter is in preparation for publication. r N = r P Neutron Skin = R N - R P = fm Preliminary: Awaiting the final acceptance function 23

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R. Michaels, Jlab PAVI-11 PREX-II Approved by PAC (Aug 2011) A Rating 35 days run in 2013 / 2014

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R. Michaels, Jlab PAVI-11 Collimators Septum Magnet target HRS-L Q1 HRS-R Q1 PREX Region After Target Former O-Ring location which failed & caused time loss during PREX-I PREX-II to use all-metal seals Tungsten Collimator & Shielding Improvements for PREX-II

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R. Michaels, Jlab PAVI-11 Geant 4 Radiation Calculations PREX-II shielding strategies J. Mammei, L. Zana Number of Neutrons per incident Electron Strategy Tungsten ( W ) plug Shield the W x 10 reduction in 0.2 to 10 MeV neutrons MeV Energy (MeV) --- PREX-I --- PREX-II, no shield --- PREX-II, shielded MeV MeV beamline shielding scattering chamber 26

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R. Michaels, Jlab PAVI-11 Other Nuclei ? Shape Dependence ? RNRN RNRN Surface thickness arXiv: [nucl-th] Parity Violating Electron Scattering Measurements of Neutron Densities Shufang Ban, C.J. Horowitz, R. Michaels

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R. Michaels, Jlab PAVI-11 Possible Future PREX Program ? Nucleus E (GeV) dR N / R N comment 208 Pb 1 1 %PREX-II (approved) 48 Ca 2.2 (1-pass) 0.4 % natural 12 GeV expt 48 Ca % surface thickness 40 Ca 2.2 (1-pass) 0.6 % basic check of theory tin isotope % apply to heavy ion tin isotope % surface thickness Each point 30 days stat. error only Not yet proposed. Just a what if ? arXiv: [nucl-th]Shufang Ban, C.J. Horowitz, R. Michaels

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R. Michaels, Jlab PAVI-11 Future in Hall A at JLab g2p/GEp 12 mo. Shutdown no promised beam Early Experiments Commissioning SuperBigbite Moller SOLID Beam 1 st to Hall A PREX – II ? $ $$$ $$$$

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R. Michaels, Jlab PAVI-11 PREX : Summary Fundamental Nuclear Physics with many applications PREX-I 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 PREX-II approved (runs in 2013 or 2014 we hope )

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R. Michaels, Jlab PAVI-11 Extra Slides

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R. Michaels, Jlab PAVI-11 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.

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R. Michaels, Jlab PAVI-11 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

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R. Michaels, Jlab PAVI-11 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

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R. Michaels, Jlab PAVI-11 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

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R. Michaels, Jlab PAVI-11 Pull Plot (example) PREX Data

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R. Michaels, Jlab PAVI-11 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. FP TM1 Solid Liquid Neutron Star Crust vs Pb Neutron Skin 208 Pb Neutron Star C.J. Horowitz, J. Piekarawicz

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R. Michaels, Jlab PAVI-11 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

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R. Michaels, Jlab PAVI-11 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.

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