Precise Neutron Lifetime Measurement Using Pulsed Neutron Beams at J-PARC

TL;DR

This paper reports a new neutron lifetime measurement using a pulsed neutron beam at J-PARC, aiming to resolve discrepancies between existing methods and improve precision in fundamental physics parameters.

Contribution

It introduces a novel beam experiment with a time projection chamber at J-PARC to measure neutron lifetime more accurately, addressing systematic errors in previous methods.

Findings

First measurement using pulsed neutron beams at J-PARC

Results contribute to resolving neutron lifetime discrepancies

Data supports improved understanding of weak interaction parameters

Abstract

A neutron decays into a proton, an electron, and an anti-neutrino through the beta-decay process. The decay lifetime ($\sim$880 s) is an important parameter in the weak interaction. For example, the neutron lifetime is a parameter used to determine the |$V_{\rm ud}$| parameter of the CKM quark mixing matrix. The lifetime is also one of the input parameters for the Big Bang Nucleosynthesis, which predicts light element synthesis in the early universe. However, experimental measurements of the neutron lifetime today are significantly different (8.4 s or 4.0$\sigma$) depending on the methods. One is a bottle method measuring surviving neutron in the neutron storage bottle. The other is a beam method measuring neutron beam flux and neutron decay rate in the detector. There is a discussion that the discrepancy comes from unconsidered systematic error or undetectable decay mode, such as dark decay. A new type of beam experiment is performed at the BL05 MLF J-PARC. This experiment measured neutron flux and decay rate simultaneously with a time projection chamber using a pulsed neutron beam. We will present the world situation of neutron lifetime and the latest results at J-PARC.