Measurement of the Neutron Radius of 208Pb Through Parity-Violation in Electron Scattering

Abstract

We report the first measurement of the parity-violating asymmetry $ A_{PV} $ in the elastic scattering of polarized electrons from 208Pb. $ A_{PV} $ is sensitive to the radius of the neutron distribution (Rn). The result $\rm A_{PV} = 0.656 \pm 0.060 (stat) \pm 0.014 (syst) ppm $ corresponds to a difference between the radii of the neutron and proton distributions Rn - Rp = 0.33 +0.16 -0.18 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.