We report the first measurement of the parity-violating asymmetry APV in the elastic scattering of polarized electrons from 208Pb. APV is sensitive to the radius of the neutron distribution (Rn). The result APV=0.656±0.060(stat)±0.014(syst) ppm corresponds to a difference between the radii of the neutron and proton distributions Rn-Rp=0.33-0.18+0.16 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.
Abrahamyan, S.; Holmstrom, Timothy; and PREX Collaboration, "Measurement of the Neutron Radius of (208)Pb through Parity Violation in Electron Scattering" (2012). Chemistry and Physics Faculty Publications. 19.
Phys. Rev. Lett. 108, 112502 (2012)