Measurement of the parity-odd angular distribution of gamma rays from polarized neutron capture on Cl-35

We report a measurement of two energy-weighted gamma cascade angular distributions from polarized slow neutron capture on the Cl-35 nucleus, one parity-odd correlation proportional to (s) over right arrown.(k) over right arrow (gamma) and one parity-even correlation proportional to (s) over right arrown.(k) over right arrown x (k) over right arrow (gamma). A parity-violating asymmetry can appear in this reaction due to the weak nucleon-nucleon interaction, which mixes opposite parity S-and P-wave levels in the excited compound Cl-36 nucleus formed upon slow neutron capture. If parity-violating (PV) and parity-conserving (PC) terms both exist, the measured differential cross section can be related to them via d sigma sigma/d Omega proportional to 1 +A(gamma,PV) cos theta +A(gamma,PC) sin theta. The PV and PC asymmetries for energy-weighted gamma cascade angular distributions for polarized slow neutron capture on Cl-35 averaged over the neutron energies from 2.27-9.53 meV were measured to be A(gamma,PV) = (-23.9 +/- 0.7) x 10(-6) and A(gamma,PC) = (0.1 +/- 0.7) x 10(-6). These results are consistent with previous experimental results. Systematic errors were quantified and shown to be small compared to the statistical error. These asymmetries in the angular distributions of the gamma rays emitted from the capture of polarized neutrons in Cl-35 were used to verify the operation and data analysis procedures for the NPDGamma experiment, which measured the parity-odd asymmetry in the angular distribution of gamma s from polarized slow neutron capture on protons.