Special P-25 seminar

Date & time: Monday, January 13, 2014, 10 am
Location: A234 conference room, MPF1, TA-53
Speaker: Zhaowen Tang, Indiana University

Title: Parity Violation in polarized N-P capture

Abstract: 
Hadronic parity violation comes from the quark-quark weak inter- action inside hadrons, but it is not clear how this interaction manifests itself at the nuclear interaction scale. The understanding of this field is complicated by the large size of the strong interaction, which is 7 orders of magnitude larger. One theoretical approach to this field is the DDH model, which is a meson exchange model that characterizes hadronic parity violation in terms of a parity violating (weak) vertex and a parity conserving (strong) vertex. The model requires 6 free parameters, which, in principle, can be determined from few-body nu- clear reactions. The NPDGamma experiment measures the parity vi- olating γ asymmetry of polarized neutron capture on a para-hydrogen target. The goal of the experiment is to measure the h1π parameter in the DDH model to 20% of its estimated value of 5 ! 10!7. This requires a measurement precision of 1 ! 10!8 on the asymmetry, Aγ . The experiment is currently running at the Spallation Neutron Source at Oak Ridge National Lab, and it will be an order of 20 improvement from the last measurement, which was performed at LANSCE. I will report the status of the NPDGamma experiment, with particular at- tention to the 16 L para-hydrogen target and the determination of Al asymmetry, which is the biggest source of background to Aγ.