Measurement of the Free Neutron Lifetime in a Magneto-Gravitational Trap with In Situ Detection

TL;DR

This paper reports a precise measurement of the free neutron lifetime using a magneto-gravitational trap with in situ detection, analyzing three years of data to reduce uncertainties and improve statistical accuracy.

Contribution

It presents an updated neutron lifetime measurement with reduced systematic uncertainties and explores different detector geometries to understand phase space effects.

Findings

Neutron lifetime measured as 877.82+/-0.22 (stat) +0.20-0.17 (sys) seconds.

Improved detector setup reduced systematic uncertainties.

Multiple detector geometries tested to assess phase space evolution effects.

Abstract

Here we publish three years of data for the UCNtau experiment performed at the Los Alamos Ultra Cold Neutron Facility at the Los Alamos Neutron Science Center. These data are in addition to our previously published data. Our goals in this paper are to better understand and quantify systematic uncertainties and to improve the lifetime statistical precision. We report a measured value for these runs from 2020-2022 for the neutron lifetime of 877.94+/-0.37 s; when all the data from UCNtau are averaged we report an updated value for the lifetime of 877.82+/-0.22 (statistical)+0.20-0.17 (systematic) s. We utilized improved monitor detectors, reduced our correction due to UCN upscattering on ambient gas, and employed four different main UCN detector geometries both to reduce the correction required for rate dependence and explore potential contributions due to phase space evolution.