Gordon Conference MAD poster

1
208
PREX Pb Radius Experiment
JLab Hall A Collaboration
Proposal to measure the RMS radius of
the neutron distribution of lead
through parity violating elastic
scattering.
R. Michaels (JLab), P.A. Souder (Syracuse),
G.M. Urciuoli (INFN), C.J. Horowitz (Indiana)
http//hallaweb.jlab.org/parity/prex
2
Low Q elastic e - nucleus scattering
E 850 MeV
0
Z
Couples Mainly to Neutrons
(weak interaction)
(T.W. Donnelly, J. Duback, I. Sick).
L R Polarized Electrons
(C. J. Horowitz)
(C. J. Horowitz)

• Applications
• Fundamental Check of
• Input to Atomic PV Expts
• Neutron Star Structure

Crab Nebula (neutron star)
Neutron Star
Nuclear Theory
208
Pb
R constrains pressure of neutron matter.
Can predict radius of neutron star and other
properties.
N
R is necessary input to precision atomic
tests of the Standard Electroweak Model.
(Horowitz, Piekarewicz, Carriere)
N
2
Meaurement at one Q constrains R
N

• Neutron star has a solid crust over a
  liquid core.
• Heavy nuclei have a neutron skin
• Both neutron stars and neutron skins are
  made from neutron rich matter at similar
  densities.
• Common unknown Equation of state (EOS)
  at subnuclear densities.
• Neutron radius measurement constrains URCA
  cooling of NS by determining the
  density dependence of the symmetry energy.

Thick neutron skin in Pb ? Low transition
density in neutron star.
Rn-Rp in 208Pb
Measurement of R determines the symmetry
energy and its density dependence.
N

• Experimental Aspects
• Spectrometer and Integrating DAQ of
  HAPPEX
• Septum magnet at 6 to increase
  figure of merit.
• New high power Lead Target

(R. J. Furnstahl)
Proton fraction Y in neutron star as
constrained by R - R
P
N
P
Choice of Kinematics
Lead Target
Successfully tested at 80 A
208
Pb
Liquid Helium Coolant
12
C
Electron Beam
Diamond Backing

• High Thermal Conductivity
• Negligible Systematics

Electron Beam