Setting bounds on a fifth force: Some extensions to the Standard Model of particle physics posit the existence of a fifth force to complement the existing four fundamental forces. To set bounds on the strength of such an interaction, experiments on vastly different length scales have been performed. Heacock et al . used an unusual method called Pendellösung interferometry to measure the neutron structure factors of silicon. The momentum dependence of the structure factors enabled the researchers to put more stringent bounds on the strength of a type of fifth force called the Yukawa force, as well as measure the charge radius of the neutron. —JS

An $sp$-mixing model, which describes a compound nuclear reaction by mixing partial waves, predicts a correlation term in this reaction. A detailed study of the $sp$-mixing model is required to study the feasibility of a new type of time reversal symmetry violation search experiment. The correlation term ${\mathit{\sigma }}_n·\left({\mathit{k}}_n\times {\mathit{k}}_{\gamma }\right)$ in the ${}^{139}\mathrm{La}(\vec{n},\gamma )$ reaction has been studied by measuring $\gamma$-ray and neutron energies utilizing epithermal polarized neutrons and germanium detectors. The transverse asymmetry for single $\gamma$-ray transition was measured to be $0.60\pm 0.19$ in the $p$-wave resonance.

A cold-neutron interferometer using four independent multilayer mirrors is demonstrated. We have observed interference fringes with a contrast of 60%. The interferometer is based on a pair of devices using etalons with an air gap of $9.75\mu \mathrm{m}$ in spacing. The optical system is equivalent to the Jamin-type interferometer, which allows much larger spatial separation between the two coherent beams than the previous type of multilayer interferometer to broaden the applicability of neutron interferometry.

A new time projection chamber (TPC) was developed for neutron lifetime measurement using a pulsed cold neutron spallation source at the Japan Proton Accelerator Research Complex (J-PARC). Managing considerable background events from natural sources and the beam radioactivity is a challenging aspect of this measurement. To overcome this problem, the developed TPC has unprecedented features such as the use of polyether-ether-ketone plates in the support structure and internal surfaces covered with $^6$Li-enriched tiles to absorb outlier neutrons. In this paper, the design and performance of the new TPC are reported in detail.Comment: 33 pages, 10 figure

Largely enhanced parity-violating effects observed in compound resonances induced by epithermal neutrons are currently attributed to the mixing of parity-unfavored partial amplitudes in the entrance channel of the compound states. Furthermore, it is proposed that the same mechanism that enhances the parity violation also enhances the breaking of time-reversal invariance in the compound nucleus. The entrance-channel mixing induces energy-dependent spin-angular correlations of individual $\gamma$ rays emitted from the compound nuclear state. For a detailed study of the mixing model, the $\gamma$-ray yield in the reaction of ${}^{117}\mathrm{Sn}(n,\gamma ){}^{118}\mathrm{Sn}$ was measured using a pulsed beam of polarized epithermal neutrons and Ge detectors. An angular dependence of asymmetric $\gamma$-ray yields for the orientation of the neutron polarization was observed.

Inverse Compton scattering of polarized laser photons by energetic electrons is an excellent method to generate polarized gamma rays. A 100% polarized laser can generate 100% polarized gamma rays, but polarization varies depending on the scattering angle of the gamma rays. In this study, we experimentally measure the spatial polarization distribution of circularly polarized gamma rays using a magnetized iron that can measure the circular polarization of MeV gamma rays. Measurements of the asymmetry of gamma-ray transmission relative to the magnetized iron at each scattering angle clearly show that gamma rays are circularly polarized near the central axis, and they change from circular to linear polarization as the scattering angle increases. A simple way to obtain highly polarized gamma rays is to use a collimator that transmits only the central axis of the gamma rays with such polarization characteristics. Polarized gamma rays are, indeed, generated by ${90}^{\circ }$ collisional inverse Compton scattering between an electron beam and a circularly polarized laser.