Measurement of the parity-odd angular distribution of γ rays from polarized neutron capture on Cl35

Abstract

We report a measurement of two energy-weighted γ cascade angular distributions from polarized slow neutron capture on the Cl35 nucleus, one parity-odd correlation proportional to sn⃗·kγ⃗ and one parity-even correlation proportional to sn⃗·kn⃗×kγ⃗. 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 Cl36 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 dσdΩ∝1+Aγ,PVcosθ+Aγ,PCsinθ. The PV and PC asymmetries for energy-weighted γ cascade angular distributions for polarized slow neutron capture on Cl35 averaged over the neutron energies from 2.27–9.53 meV were measured to be Aγ,PV=(−23.9±0.7)×10−6 and Aγ,PC=(0.1±0.7)×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 γ rays emitted from the capture of polarized neutrons in Cl35 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 γs from polarized slow neutron capture on protons.5 MoreReceived 1 October 2021Accepted 17 May 2022DOI:https://doi.org/10.1103/PhysRevC.106.015504©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear spin & parityNuclear tests of fundamental interactionsPolarization phenomenaRadiative captureProperties20 ≤ A ≤ 38TechniquesParticle sources & targetsNuclear Physics