PREX and CREX. R N from Electroweak Asymmetry in Elastic Electron-Nucleus Scattering. Neutron Skin.

Transcription

1 PREX and CREX 08 Pb Horowitz 48 Ca Neutron Skin R N from Electroweak Asymmetry in Elastic Electron-Nucleus Scattering R L 4 6 A ~ 10 PV Q ~ 10 R L PRL 108 (01) 1150 R P R N (fm) X. Roca-Maza J. Piekarewicz L = density dependence of symmetry energy

2 target PREX and CREX in Hall A at Jefferson Lab Improved shielding and vacuum seals spectrometers Current Status Both experiments approved PREX A rating 35 days CREX A- rating 45 days Systematic Error Goals for PREX-II demonstrated by PREX-I Improved designs for vacuum seals and radiation shielding PREX target lead / diamond foils CREX target 08 Pb procured, 48 Ca designed PAC 014: PREX is among the high impact experiments at Jlab. but CREX didn t make that list. 48 Ca

3 PREX and CREX 08 Pb 48 Ca A PV R R L L ~ 10 4 Q ~ 10 6 e Pb e Z 08 Pb A G F Q 1 4sin W F F N P ( Q ( Q Electroweak Asymmetry in Elastic Electron-Nucleus Scattering : a measure of neutron distribution ) ) Horowitz Neutron Skin R n R p r n r p correlated with the EOS of neutron matter X. Roca-Maza Density dependence of symmetry energy, L

4 A PV PREX-I ppm 0.060( stat) 0.013( syst) R n PRL 108 (01) 1150 R p fm PREX-II / CREX Approved proposals at JLab Rp Rn (fm) Neutron skin is highly correlated with neutron star properties J. Piekarewicz, arxiv

5 PREX and CREX 48 Ca 08 Pb e Pb Target Criteria First excited state far from elastic Neutron excess Doubly-magic Stable e Z 08 Pb 08 Pb A G Q F F Q Q R L F W PV ~ ~ 1 R L 4 chg ppm Electroweak Asymmetry in Elastic Electron-Nucleus Scattering -- Weak charge form factor -- most weak charge is carried by neutrons PRL 108 (01) Ca Rn (fm) High Resolution Spectrometers in Hall A at

6 M ( M solar ) E/N (MeV) Using models, one can relate the neutron star radius to the neutron skin of heavy nuclei Gandolfi et al. PRC85, (01) Neutron density Neutron EOS. How to extrapolate to higher densities like Heavy Ion Collisions or Neutron Stars? R n R p PREX I fm PREX II

7 +/- 0.0 fm PREX-II / CREX PREX-II and CREX are approved to run at JLab PREX A rating 35 days in ~016 CREX A- rating 45 days date uncertain 0.06 fm Systematic Error Goals for PREX-II demonstrated by PREX-I. J. Piekarewicz, arxiv PAC 014: PREX is among the high impact experiments at JLab. but CREX not Needs? These fit into the Jlab budget spread over a few years. We already procured 08 Pb and septum repairs. -- PREX-II needs shielding, vacuum chamber, diamond foils, collimators. -- CREX needs 48 Ca (loaned), target vessel, proposed to use PREX septum.

8 Hall A at Jefferson Lab Hall A Hall A B C

9 Parity Violating Asymmetry A PV R R L L ~ 10 4 Q ~ 10 6 e Pb e Z 08 Pb A PV from interference Applications of A PV at Jefferson Lab Nucleon Structure Strangeness s s in proton (HAPPEX, G0 expts) Test of Standard Model of Electroweak e e (MOLLER) or e q (PVDIS) elastic e p at low Q (QWEAK) sin W This talk Nuclear Structure (neutron density) : PREX 8/53

10 ) ( 4sin 1 Q F Q G d d d d d d d d A P W F L R L R ) ( Q F n 1% % 3 n n R dr A da 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) : 0

11 PREX Physics Output Measured Asymmetry Correct for Coulomb Distortions Weak Density at one Q Atomic Parity Violation Small Corrections for G n E G s E MEC Neutron Density at one Q Mean Field & Other Models Slide adapted from C. Horowitz Assume Surface Thickness Good to 5% (MFT) R n Neutron Stars

12 Reminder: Electromagnetic Scattering determines r d d d d mb str 08 Pb r (charge distribution) 1 3 q fm 1 1/53

13 Z 0 of weak interaction : sees the neutrons proton neutron T.W. Donnelly, J. Dubach, I. Sick Nucl. Phys. A 503, 589, 1989 Electric charge 1 0 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, 05501, 001 Weak charge Neutron form factor F 1 3 ) d r j ( qr) N ( r) 4 N ( Q 0 Parity Violating Asymmetry A G FQ 1 4sin W 0 F F N P ( Q ( Q ) ) C.J. Horowitz 10

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

15 Inputs: Eq. of state (EOS) P() PREX helps here Hydrostatics (Gen. Rel.) Astrophysics Observations Luminosity L Temp. T Mass M from pulsar timing L 4 4 B R T (with corrections ) Mass - Radius relationship Fig from: Dany Page. J.M. Lattimer & M. Prakash, Science 304 (004) 536.

16 PREX & Neutron Stars 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 Phase Transition to Exotic Core? Strange star? Quark Star? Some Neutron Stars seem too cold Explained by Cooling by neutrino emission (URCA process)? R n R p 0. fm URCA probable, else not Crab Pulsar

17 Nuclear Structure: Slide adapted from J. Piekarewicz Neutron density is a fundamental observable that remains elusive. Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of N Z E( n, x) E( n, x 1/ ) S ( n) (1 x ) n n.m. density x ratio proton/neutrons Slope unconstrained by data 08 Adding R N from Pb will significantly reduce the dispersion in plot. 15

18 Thanks, Alex Brown PREX Workshop 008 Skx-s15 E/N N

19 Thanks, Alex Brown PREX Workshop 008 Skx-s0 E/N N

20 Thanks, Alex Brown PREX Workshop 008 Skx-s5 E/N N

21 Application: Atomic Parity Violation Low Q test of Standard Model Needs R N (or APV measures R N ) Isotope Chain Experiments e.g. Berkeley Yb H PNC G F / 5 3 N ( r) Z (1 4sin ) ( r) d r N W P e e 0 APV Momentum transfer 1/53

22 PREX Setup Parity: The entire lab is the experiment Spectometers Lead Foil Target Hall A JLAB Pol. Source CEBAF 5/53

23 How to do a Parity Experiment (integrating method) Flux Integration Technique: HAPPEX: MHz PREX: 500 MHz Example : HAPPEX

24 Beam Asymmetries A raw = A det - A Q + E + i x i Slopes from natural beam jitter (regression) beam modulation (dithering) PAVI 09 31

25 Points: Not sign corrected Parity Quality Beam! ( why we love Jlab! ) Helicity Correlated Position Differences Average with signs = what exp t feels < ~ 3 nm X R X L for helicity L, R Units: microns Slug # ( ~ 1 day)

26 Hall A High Resolution Spectrometers Resolve Elastic Scattering Discriminate Excited States Elastic Inelastic detector Pure, Thin 08 Pb Target.6 MeV target Quads Dipole DETECTOR footprint Scattered Electron s Momentum (GeV/c)

27 Detector Package in HRS PREX Integrating Detectors DETECTORS UMass / Smith

28 Lead / Diamond Target Diamond LEAD Three bays Lead (0.5 mm) sandwiched by diamond (0.15 mm) Liquid He cooling (30 Watts)

29 PREX Asymmetry (P e x A) ppm Slug ~ 1 day

30 Asymmetry leads to R N Establishing a neutron skin at ~95 % CL * Neutron Skin = R N - R P = fm fig from C.J. Horowitz PREX data * Interpretation requires the acceptance function for spectrometer: ( )

31 Possible Future PREX Program? Each point 30 days stat. error only Nucleus E (GeV) dr N / R N comment 08 Pb 1 1 % PREX-II (approved by Jlab PAC, A rating) 48 Ca. (1-pass) 0.4 % natural 1 GeV exp t will next PAC 48 Ca.6 % surface thickness 40 Ca. (1-pass) 0.6 % basic check of theory tin isotope % apply to heavy ion tin isotope % surface thickness Not proposed Shufang Ban, C.J. Horowitz, R. Michaels J. Phys. G

32 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 013 or 014 )