Fundamental physics activities with pulsed neutron at J-PARC(BL05)

TL;DR

This paper describes the development of a neutron physics beamline at J-PARC for fundamental physics experiments, including neutron lifetime measurement, ultra-cold neutron sources, and searches for unknown forces, with advancements in detector technology.

Contribution

It introduces new experimental setups and methods for neutron lifetime measurement, ultra-cold neutron production, and high-resolution neutron detection at J-PARC's beamline.

Findings

Successful development of a neutron lifetime measurement method with 0.1% uncertainty.

Implementation of a pulsed ultra-cold neutron source using a Doppler shifter.

Detection of cold and ultra-cold neutrons with a novel emulsion detector.

Abstract

"Neutron Optics and Physics (NOP/ BL05)" at MLF in J-PARC is a beamline for studies of fundamental physics. The beamline is divided into three branches so that different experiments can be performed in parallel. These beam branches are being used to develop a variety of new projects. We are developing an experimental project to measure the neutron lifetime with total uncertainty of 1 s (0.1%). The neutron lifetime is an important parameter in elementary particle and astrophysics. Thus far, the neutron lifetime has been measured by several groups; however, different values are obtained from different measurement methods. This experiment is using a method with different sources of systematic uncertainty than measurements conducted to date. We are also developing a source of pulsed ultra-cold neutrons (UCNs) produced from a Doppler shifter are available at the unpolarized beam branch. We are developing a time focusing device for UCNs, a so called "rebuncher", which can increase UCN density from a pulsed UCN source. At the low divergence beam branch, an experiment to search an unknown intermediate force with nanometer range is performed by measuring the angular dependence of neutron scattering by noble gases. Finally the beamline is also used for the research and development of optical elements and detectors. For example, a position sensitive neutron detector that uses emulsion to achieve sub-micrometer resolution is currently under development. We have succeeded in detecting cold and ultra-cold neutrons using the emulsion detector.