Improved neutron lifetime measurement with UCN$\tau$

TL;DR

This paper presents an improved measurement of the free neutron lifetime using the UCNτ apparatus, achieving high precision and consistency through multiple analysis methods, which helps refine the understanding of neutron decay within the Standard Model.

Contribution

The study introduces a new high-precision measurement of the neutron lifetime using a magneto-gravitational trap and blinded analyses, reducing systematic uncertainties compared to previous experiments.

Findings

Measured neutron lifetime: 877.75 ± 0.28 (stat) +0.22/-0.16 (syst) seconds.

Consistent results from multiple independent analysis techniques.

Enhanced experimental sensitivity addresses recent theoretical refinements in neutron decay.

Abstract

We report an improved measurement of the free neutron lifetime $\tau_{n}$ using the UCN$\tau$ apparatus at the Los Alamos Neutron Science Center. We counted a total of approximately $38\times10^{6}$ surviving ultracold neutrons (UCN) after storing in UCN$\tau$'s magneto-gravitational trap over two data acquisition campaigns in 2017 and 2018. We extract $\tau_{n}$ from three blinded, independent analyses by both pairing long and short storage-time runs to find a set of replicate $\tau_{n}$ measurements and by performing a global likelihood fit to all data while self-consistently incorporating the $\beta$-decay lifetime. Both techniques achieve consistent results and find a value $\tau_{n}=877.75\pm0.28_{\text{ stat}}+0.22/-0.16_{\text{ syst}}$~s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.