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.

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.

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

nuclear-matter incompressibility, J. Piekarewicz to be published.

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.

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