Accurate Determination of the Neutron Skin Thickness of 208Pb through Parity-Violation in Electron Scattering

We report a precision measurement of the parity-violating asymmetry A(pv) in the elastic scattering of longitudinally polarized electrons from Pb-208. We measure A(pv) = 550 +/- 16(stat) +/- 8(syst) parts per billion, leading to an extraction of the neutral weak form factor F-w (Q(2) = 0.00616 GeV2) = 0.368 +/- 0.013. Combined with our previous measurement, the extracted neutron skin thickness is R-n - R-p = 0.283 +/- 0.071 fm. The result also yields the first significant direct measurement of the interior weak density of Pb-208: rho(0)(w) = -0.0796 +/- 0.0036(exp) +/- 0.0013(theo) fm(-3) leading to the interior baryon density rho(0)(w)= 0.1480 +/- 0.0036(exp) +/- 0.0013(theo) fm(-3). The measurement accurately constrains the density dependence of the symmetry energy of nuclear matter near saturation density, with implications for the size and composition of neutron stars.

Automated summary

The study reports a precise measurement of the parity-violating asymmetry A(pv) in elastic scattering of longitudinally polarized electrons from Pb-208, extracting key parameters such as neutron skin thickness and interior baryon density. This measurement accurately constrains the density dependence of the symmetry energy of nuclear matter near saturation density, with implications for the size and composition of neutron stars.