A modular apparatus for use in high-precision measurements of parity violation in polarized eV neutron transmission

Abstract

We describe a modular apparatus for use in parity-violation measurements in epithermal neutron-nucleus resonances with high instantaneous neutron fluxes at the Manuel Lujan Jr. Neutron Scattering Center at Los Alamos National Laboratory. This apparatus is designed to conduct high-precision measurements of the parity-odd transmission asymmetry of longitudinally polarized neutrons through targets containing nuclei with p-wave neutronnucleus resonances in the 0.1-10 eV energy regime and to accommodate a future search for time reversal violation in polarized neutron transmission through polarized nuclear targets. The apparatus consists of an adjustable neutron and gamma collimation system, a 3 He-4 He ion chamber neutron flux monitor, two identical cryostats for target cooling, an adiabatic eV-neutron spin flipper, a near-unit efficiency 6 Li-7 Li scintillation detector operated in current mode, a flexible CAEN data acquisition system, and a neutron spin filter based on spin-exchange optical pumping of 3 He gas. We describe the features of the apparatus design devoted to the suppression of systematic errors in parity-odd asymmetry measurements. We describe the configuration of the apparatus used to conduct a precision measurement of parity violation at the 0.7 eV p-wave resonance in 139 La which employs two identical 139 La targets, one to polarize the beam on the p-wave resonance using the weak interaction and one to analyze the polarization.

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“…'Delta-Rice' was designed to meet these requirements and was implemented as an HDF5 filter plugin to ensure that each user can easily access data with minimal additional requirements in multiple programming languages (Mathews, 2022). While many other filter plugins exist for HDF5 files, such as Bitshuffle (Masui et al, 2015) and Gzip, Delta-Rice offers improved throughput and reduction in data size for many experimental efforts such as the Nab, NOPTREX (Schaper et al, 2020), and nEDM@SNS (Ahmed et al, 2019) efforts.…”

Strong CP violation in nuclear physics

“…S is antisymmetric in the S-P and P -D elements due to time-reversal violation. The CP -odd mixing angles 0,1 SP and DP are in principle observable in, for example, spin rotation of polarized ultracold neutrons on a polarized hydrogen target [43], but it is unlikely that these experiments can reach a sensitivity that is competitive with EDM experiments, although neutron transmission experiments using heavy target nuclei might be up to the task [44,45]. Nuclear EDMs can be written as linear combinations of the mixing angles in addition to contributions from CP-odd electromagnetic currents such as constituent nucleon EDMs.…”