Measurement of the Parity Violating Asymmetry in Elastic Electron Scattering off 208Pb

MEASUREMENT OF THE PARITY VIOLATING ASYMMETRY IN ELASTIC ELECTRON SCATTERING OFF Pb SEPTEMBER 2014 JONATHAN WILLIAM WEXLER, JR., B.A., HAMILTON COLLEGE M.S., UNIVERSITY OF MASSACHUSETTS AMHERST PH.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by Krishna Kumar The Lead Radius Experiment (PREX) was carried out in order to provide a modelindependent measurement of the RMS radius √ 〈r2 n〉 of the neutron distribution in the Pb nucleus. The parity-violating scattering asymmetry for longitudinally polarized 1.06 GeV electrons from an unpolarized Pb target was measured at Q = 0.00880 GeV. This measurement was performed by the PREX collaboration in Hall A at Jefferson Laboratory in Newport News, VA, between March and June, 2010. The electron detectors used in this measurement were designed and fabricated by University of Massachusetts-Amherst and Smith College. The resulting parity-violating asymmetry was measured as APV = 656± 60(stat.)± 14(sys.) ppb. This asymmetry extrapolates to a difference in radii between the nuclear neutron and proton distributions of √ 〈r2 n〉 √〈 r2 p 〉 = 0.33 −0.18 fm.