Nuclear Physics Seminars

Parity violation (PV) was first observed in semileptonic beta decays, and has been mapped out precisely at the quark and lepton level as part of the standard model. However, PV in hadronic systems has proven much more elusive, where the strong interaction dominates by seven orders of magnitude. These weak contributions have been classified in chiral effective field theory in terms of the spin and isospin dependence of transition amplitudes involving S and P waves. There is an active program to determine the EFT parameters by measuring hadronic PV using cold neutron beams at the Spallation Neutron Source (ORNL) and the NCNR reactor (NIST). These experiments use only few-body observables, for which nuclear wave functions are calculable. The NPDGamma experiment recently completed taking data of the PV gamma spin asymmetry in the reaction n + p -> d + gamma. We have commissioned the follow-up experiment n3He to measure the proton spin asymmetry in the reaction n + 3He -> 3H + p. These two experiments, along with elastic PV proton-proton scattering, will help isolate the four dominant contributions to the PV hadronic weak interaction.