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Thomas Jefferson National Accelerator Facility

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Presentation on theme: "Thomas Jefferson National Accelerator Facility"— Presentation transcript:

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

2 Z0 of weak interaction : sees the neutrons
T.W. Donnelly, J. Dubach, I. Sick proton neutron Electric charge 1 Weak charge 0.08 Nucl. Phys. A 503, 589, 1989 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, , 2001 Neutron form factor C.J. Horowitz Parity Violating Asymmetry

3 Hall A at Jefferson Lab Hall A

4 PREX Physics Output Mean Field & Other Atomic Parity Violation Models
Measured Asymmetry Physics Output Correct for Coulomb Distortions Weak Density at one Q 2 Mean Field Small Corrections for n s & Other Atomic Parity Violation G G MEC E E Models 2 Neutron Density at one Q Assume Surface Thickness Good to 25% (MFT) Neutron Stars Slide adapted from C. Horowitz R n

5 Slide adapted from J. Piekarewicz
Nuclear Structure: Neutron density is a fundamental observable that remains elusive. Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of ratio proton/neutrons n.m. density Slope unconstrained by data Adding R from Pb will eliminate the dispersion in plot. 208 N 5

6 Thanks, Alex Brown PREX Workshop 2008 Skx-s15 E/N

7 Thanks, Alex Brown PREX Workshop 2008 Skx-s20 E/N

8 Thanks, Alex Brown PREX Workshop 2008 Skx-s25 E/N 8

9 APV Application: Atomic Parity Violation Low Q test of Standard Model
Needs RN (or APV measures RN ) 2 Isotope Chain Experiments e.g. Berkeley Yb APV 9

10 PREX & Neutron Stars C.J. Horowitz, J. Piekarewicz RN calibrates equation of state (pressure vs density) of Neutron Rich Matter Combine PREX RN with Observed Neutron Star Radii Fig from: Dany Page J.M. Lattimer & M. Prakash, Science 304 (2004) 536. 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 Crab Pulsar

11 PREX Overview Spectometers Lead Foil Target Hall A JLAB CEBAF
Parity: “The entire lab is the experiment” CEBAF Hall A JLAB Pol. Source Spectometers Lead Foil Target

12 Parity Quality Beam ! < ~ 3 nm ( why we love Jlab ! )
Helicity – Correlated Position Differences < ~ 3 nm Points: Not sign corrected Average with signs = what exp’t feels Units: microns Slug # ( ~ 1 day)

13 Flips spin without moving the beam !
Double Wien Filter (NEW for PREX) Crossed E & B fields to rotate the spin Two Wien Spin Manipulators in series Solenoid rotates spin +/-90 degrees (spin rotation as B but focus as B2). Flips spin without moving the beam ! Electron Beam SPIN Joe Grames, et. al. 13

14 Hall A Compton Upgrade 1 % Polarimetry at 1 GeV with Green Laser
Sirish Nanda, et. al. (Megan Friend’s talk) 1 % Polarimetry at GeV

15 Hall A Moller Upgrade < 1 % Polarimetry Magnet and Target
Superconducting Magnet from Hall C Saturated Iron Foil Targets < 1 % Polarimetry Sasha Glamazdin, (talk Thurs) DAQ Upgrade (FADC)

16 Hall A High Resolution Spectrometers
Resolve Elastic Scattering Discriminate Excited States Elastic detector Inelastic Pure, Thin Pb Target 2.6 MeV target Dipole DETECTOR footprint Quads Scattered Electron’s Momentum (GeV/c) 16

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

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

19 + - Beam-Normal Asymmetry in elastic electron scattering
i.e. spin transverse to scattering plane y z x + - AT > 0 means Possible systematic if small transverse spin component New results PREX Preliminary ! Publication in preparation Small AT for 208Pb is a big (but pleasant) surprise. AT for 12C qualitatively consistent with 4He and available calculations (1) Afanasev ; (2) Gorchtein & Horowitz 19

20 PREX-I Result Statistics limited ( 9% )
Systematic Errors Error Source Absolute (ppm) Relative ( % ) Polarization (1) 0.0071 1.1 Beam Asymmetries (2) 0.0072 Detector Linearity BCM Linearity 0.0010 0.2 Rescattering 0.0001 Transverse Polarization 0.0012 Q2 (1) 0.0028 0.4 Target Thickness 0.0005 0.1 12C Asymmetry (2) 0.0025 Inelastic States TOTAL 0.0130 2.0 Statistics limited ( 9% ) Systematic error goal achieved ! (2%) (1) Normalization Correction applied (2) Nonzero correction (the rest assumed zero) 20

21 PREX Asymmetry (Pe x A) ppm Slug ~ 1 day

22 * * Asymmetry leads to RN
Establishing a neutron skin at ~90 % CL * Neutron Skin = RN - RP = fm fig from C.J. Horowitz PREX data * Preliminary: Awaiting the “final” acceptance function:

23 PREX-I Result, cont. Neutron Skin = RN - RP = 0.31 + 0.15 - 0.17 fm
DATA rN - rP (fm) theory: P. Ring rN = rP Atomic Number, A DATA Preliminary: Awaiting the “final” acceptance function A physics letter is in preparation for publication. 23

24 PREX-II Approved by PAC (Aug 2011)
“A” Rating days run in 2013 / 2014

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

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

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

28 Possible Future PREX Program ?
Each point 30 days stat. error only Nucleus E (GeV) dRN / RN comment 208Pb 1 1 % PREX-II (approved) 48Ca 2.2 (1-pass) 0.4 % natural 12 GeV exp’t 2.6 2 % surface thickness 40Ca 0.6 % basic check of theory tin isotope 1.8 apply to heavy ion 1.6 % Not yet proposed. Just a “what if ?” Shufang Ban, C.J. Horowitz, R. Michaels arXiv:   [nucl-th]

29 Future in Hall A at JLab PREX – II ? Early Experiments g2p/GEp
12 mo. Shutdown no promised beam Commissioning SuperBigbite $ Beam 1st to Hall A Moller $$$ SOLID $$$$ PREX – II ? 2011 2012 2013 2014 2015 2016 2017 2018

30 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 or we hope )

31 Extra Slides

32 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 Involve strong probes Most spins couple to zero. MFT fit mostly by data other than neutron densities

33 Parity Violating Asymmetry
Electron - Nucleus Potential electromagnetic axial is small, best observed by parity violation 208 Pb is spin 0 neutron weak charge >> proton weak charge Proton form factor Neutron form factor Parity Violating Asymmetry

34 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, PRC

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

36 Pull Plot (example) PREX Data

37 Liquid/Solid Transition Density
Neutron Star Crust vs Pb Neutron Skin FP TM1 Solid Liquid C.J. Horowitz, J. Piekarawicz Neutron Star 208Pb Thicker neutron skin in Pb means energy rises rapidly with density  Quickly favors uniform phase. Thick skin in Pb  low transition density in star.

38 Backgrounds that might re-scatter into the detector ?
Detector cutoff 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.

39 Pb PREX: pins down the symmetry energy (1 parameter) PREX error bar
energy cost for unequal # protons & neutrons PREX error bar ( R.J. Furnstahl ) Actually, it’s the density dependence of a4 that we pin down. 208 Pb PREX

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