Improved measurements of neutron lifetime with cold neutron beam at J-PARC

TL;DR

This study presents an improved measurement of neutron lifetime using a novel electron detection method at J-PARC, achieving higher precision and addressing discrepancies between existing measurement techniques.

Contribution

The paper introduces a new beam method detecting electrons instead of protons, reducing systematic uncertainties and improving measurement precision of neutron lifetime.

Findings

Neutron lifetime measured as 877.2 ± 1.7 (stat.) +4.0/-3.6 (sys.) seconds.

Results are consistent with bottle method measurements.

The measurement shows a 2.3σ tension with proton-based beam method results.

Abstract

The ``neutron lifetime puzzle'' arises from the discrepancy between neutron lifetime measurements obtained using the beam method, which measures decay products, and the bottle method, which measures the disappearance of neutrons. To resolve this puzzle, we conducted an experiment using a pulsed cold neutron beam at J-PARC. In this experiment, the neutron lifetime is determined from the ratio of neutron decay counts to $^3$He(n,p)$^3$H reactions in a gas detector. This experiment belongs to the beam method but differs from previous experiments that measured protons, as it instead detects electrons, enabling measurements with distinct systematic uncertainties. By enlarging the beam transport system and reducing systematic uncertainties, we achieved a fivefold improvement in precision. Analysis of all acquired data yielded a neutron lifetime of $\tau_{\rm n}=877.2~\pm~1.7_{\rm(stat.)}~^{+4.0}_{-3.6}{}_{\rm (sys.)}$ s. This result is consistent with bottle method measurements but exhibits a 2.3$\sigma$ tension with the average value obtained from the proton-detection-based beam method.