References for Pb208 Parity Violating Experiment (P-ReX)

C. J.. Horowitz, Indiana University

Uses parity violating electorn scattering to measure the neutron radius in Pb208 at Hall A in Jeferson Lab.
Jeferson Laboratory Experiment E00-003, R. Michaels, P. Souder, G. Urciuoli spokespersons.


Long paper giving analysys of experiment:
nucl-th/9912038, Parity Violating Measurements of Neutron Densities
C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels, Phys.Rev. C63 (2001) 025501.

Calculation of Coulomb distortions:
nucl-th/9801011, Parity Violating Elastic Electron Scattering and Coulomb Distortions
C. J. Horowitz (Indiana), Phys.Rev. C57 (1998) 3430-3436.

Original sugestion of measuring neutron densities with parity violation:
T. M. Donnelly, J. Dubach and Ingo Sick, Nuc. Phys. A503 (1989) 509.

The neutron radius measurement determines the density dependence of the symmetry energy.  
The symmetry energy determines how the energy of nuclear matter rises as one goes away from
equal numbers of neutrons and protons.  A symmetry energy that rises rapidly with density leads
to a large pressure for the neutrons in the neutron rich skin of Pb208 and this gives a large
neutron radius.  Relativistic mean filed models tend to predict a more rapid density dependence
for the symetery energy and a larger neutron radius than nonrelativitistic models.



The equation of state of neutron rich matter

The equation of state, the pressure as a function of the density, is a crucial ingreident for
neutron stars.

Measureing the neutron radius in Pb determines the pressure of neutron rich matter at
normal density.  Alternatively, assuming one nonrel. microscopic calculation of the
presure of neutron matter yields R_n-R_p=0.16 +/- 0.02 fm for the difference of the
proton and neutron radii in Pb.  [Note, unknown three-body forces could modify this
microscopic prediction.] 
B. A. Brown, Phys. Rev. Lett., 85 (2000) 5296.

This has many implications for neutron stars.  For example,
astro-ph/0010227, Neutron Star Structure and the Neutron Radius of 208Pb
C. J. Horowitz, J. Piekarewicz, Phys.Rev.Lett. 86 (2001) 5647.

A short popular article about determining properties of neutron stars from
the Pb measurement is
Adrain Cho, Newscientist 2294 (2001) 11.

nucl-th/0108036, The neutron radii of Lead and neutron stars
C. J. Horowitz, J. Piekarewicz, Phys.Rev. C64 (2001) 062802.

URCA Neutron Star Cooling and the symetry energy of Dense Matter

A large symmetry energy favors more symmetric neutron rich matter with a larger fraction of protons.  
If the proton fraction is high enough than the following so called URCA process can rapidly cool neutron
stars.  Note, neutron stars cool by neutrino emision  because of their very small surface areas.
n-> p + e + anti\nu
p+e -> n + \nu
Where the \nu anti\nu pair carry off energy.  Relativistic models with a larger neutron radius in Pb tend to allow
URCA cooling  while nonrelativistic models with a small Pb radius tend to not allow URCA cooling. 

http://arxiv.org/abs/nucl-th/0207067, Constraining URCA cooling of neutron stars from the neutron radius of 208Pb
C. J. Horowitz, J. Piekarewicz, Phys.Rev. C66 (2002) 055803

Recently the neutron star in 3C 58 was observed by the Chandra X-ray observatory to be cold.  This is the remanent from
a Supernova observed in 1181.  Hence it is only 800 years old and must have cooled quickly.  Note, this was described
in a April 11 New York Times article.
astro-ph/0204151, New Constraints on Neutron Star Cooling from Chandra Observations
Patrick Slane, David J. Helfand, Stephen S. Murray, accepted by ApJ Letters


Relationship between density dependence of symmetry energy and incompressibility from the giant monoploe resonance.

nucl-th/0205007, The long journey from the giant-monopole resonance to the
nuclear-matter incompressibility,
J. Piekarewicz to be published.


Some nuclear structure calculations of neutron densities

nucl-th/0112085, Neutron Radii in Mean-Field Models
R. J. Furnstahl.

nucl-th/0004018, Neutron density distributions for atomic parity nonconservation experiments
D. Vretenar, G.A. Lalazissis, P. Ring, Phys.Rev. C62 (2000) 045502.

nucl-th/9911024, Parity violating elastic electron scattering and neutron density
distributions in the Relativistic Hartree-Bogoliubov model

D. Vretenar, P. Finelli, A. Ventura, G.A. Lalazissis, P. Ring, Phys.Rev. C61 (2000) 064307.


Selected  proton scattering determinations of neutron densities

nucl-th/0111020, Discerning the neutron density distribution of 208Pb from nucleon elastic scattering
S. Karataglidis, K. Amos, B. A. Brown, P. K. Deb,  Phys.Rev. C65 (2002) 044306.
Note, this paper finds more sensitivity to the surface thicknes than to the neutron radius.  

If one can "calibrate" the uncertian strong interaction reaction mechanism for proton scattering with a parity
violating radius measurement one can use proton scattering to measure the neutron density in
exotic nuclei.
nucl-th/9811051, Proton Elastic Scattering and Neutron Distribution of Unstable Nuclei
 K.Kaki, S.Hirenzaki, Int.J.Mod.Phys. E8 (1999) 167-178