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Spokespersons: Juliette Mammei Robert Michaels  presenting today Kent Paschke

C-REX : Parity-Violating Measurement of the Weak Charge of 48 Ca to an accuracy of 0.03 fm. Spokespersons: Juliette Mammei Robert Michaels  presenting today Kent Paschke Seamus Riordan (contact person) Paul Souder.

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Spokespersons: Juliette Mammei Robert Michaels  presenting today Kent Paschke

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  1. C-REX : Parity-Violating Measurement of the Weak Charge of 48Ca to an accuracy of 0.03 fm Spokespersons: Juliette Mammei Robert Michaels  presenting today Kent Paschke Seamus Riordan (contact person) Paul Souder Elastic scattering -- parity-violating asymmetry -- from 48Ca at 1-pass energy using HRS + septum R. Michaels, Hall A Collaboration Meeting, June 8, 2012 1/18

  2. Parity Violating Asymmetry 2 + APV from interference 48Ca 48Ca 2/18

  3. Flux Integration Technique: HAPPEX: 2 MHz PREX: 500 MHz How to do a Parity Experiment (integrating method) Example : HAPPEX 3/18

  4. Asymmetry (ppm) Slug Small beam-related Systematics--thanks to Jlab beam quality Parity Violating Asymmetry • Offline asymmetries nearly identical to online. • Corrections tiny (here, 3 ppb) • Errors are statistical only HAPPEX-II data D. Lhuillier, K. Kumar spokespersons (~1 day) Araw = -1.58 ppm 0.12 (stat)  0.04 (syst) HAPPEX-II data (HWP = optical element used to flip beam helicity, helps suppress some systematics) 4/18

  5. Parity Quality Beam : Unique Strength of JLab Helicity – Correlated Position Differences Plotted below Araw = Adet - AQ +  E+ i xi Measured separately Points: Not sign-corrected. 20-50 nm diffs. with pol. source setup & feedback Sign flips using ½ wave plate & Wien filter ++ -++--- This BPM, Average = 2.4 3.1 nm Sign flips provide further suppression : Average with signs = what experiment feels achieved < 5 nm Units: microns PREX data Slug # ( ~ 1 day) 5/18

  6. C-REX (&PREX): Z0 of weak interaction : sees the neutrons T.W. Donnelly, J. Dubach, I. Sick Nucl. Phys. A 503, 589, 1989 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, 025501, 2001 Neutron form factor C.J. Horowitz Parity Violating Asymmetry 6/18

  7. C-REX, PREX & Neutron Stars C.J. Horowitz, J. Piekarewicz RN calibrates equation of state (pressure vs density) of Neutron Rich Matter Combine C-REX / PREX RN 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) ? 0.2 fm URCA probable, else not 7/18 Crab Pulsar

  8. Pol. Source Hall A JLAB CEBAF Reminder: PREX-I Results PRL 108 (2012) 112502 HRS + septum Physics Asymmetry Pb target • Statistics limited ( 9% ) • Systematic error goal achieved ! (2%) HRS Septum Magnet 50 Pb target 8/18

  9. Asymmetry leads to RN Establishing a neutron skin at ~95 % CL Neutron Skin = RN - RP = 0.33 + 0.16 - 0.18 fm published Proposed at last PAC Spokespersons K. Kumar R. Michaels K. Paschke P. A. Souder G. Urciuoli Next, presenting a new 48Ca proposal …

  10. C-REX Target • Isotopically pure 48 Ca • Vacuum seal to trap atoms if beam destroys target • Higher thermal conductivity and melting point than lead : should take 100 uA. • Similar in concept to target used in E08014 (at 40 uA) 10/18

  11. Why 48Ca ? Why 208Pb ? Why both ? 11/18

  12. C-REX: Optimization of Kinematics (part I) Rate = 80 MHz / HRS  easy Sensitivity of Asymmetry (A) to change in RN 2.2 GeV = 1-pass ~2x more sensitive than PREX A ~ 2 ppm  “big” (easy) 12/18

  13. C-REX Optimization of FOM (part II) equivalent to minimum error in RN 2.8% stat. err. E = 2.2 GeV (1-pass) 0.03 fm total error Error in RN(units: fm) Percent Error in RN 0.9% total err. 13/18

  14. Neutron Skin vs Mass Number A C-REX PREX-I Proposed here PREX-II published Proposed at last PAC RN – RP(fm) A 14/18

  15. C-REXandPREX results expected to be correlated. Similar sensitivity to nuclear structure. PREX-II C-REX I Reminder : PREX-I result : rskin = rn-rp = 0.33 + 0.16 – 0.18 fm credit Piekarewicz, et al., PRC 85, 041302 (2012) PREX-II expects : +/- 0.05 fm C-REX (this proposal): +/- 0.03 fm 15/18

  16. Septum Magnet Room temperature Need a good dipole  hardware resolution A 50 septum (ala PREX) would work, but need a non-standard energy (1.8 GeV) 16/18

  17. Radiation Load in Hall A C-REX much lower than PREX Geant4 simulations J. Mammei C-REX vs PREX x10 fewer neutrons or photons, comparable electrons

  18. Conclusions : C-REX Fundamental Nuclear Physics with Applications to Neutron Stars and other fields which need to know about neutrons (heavy ions, atomic parity violation) 48Ca: the next nucleus for Parity-Violating Neutron Density Measurements. An accuracy of 0.03 fm will have a big impact on nuclear structure theory. R. Michaels, Hall A Collaboration Meeting, June 8, 2012

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