Analysis of the latest UCNτ dataset for neutron lifetime measurement

Beta decay of a free neutron is the simplest form of "semi-leptonic" weak interaction and is free from nuclear structure effects. Despite the simplicity of the process, its lifetime measurement remains one of the most challenging measurements, bearing different results depending on the technique ("bottle" or "beam"). Another critical measurement from the decay is the correlation (A_o) between the neutron's initial spin and emitted electron's momentum. Neutron lifetime and axial coupling constant determined using A_o are inputs to determine the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element (V_ud), and provide a means to study physics beyond the Standard Model.

UCNτ is an experiment utilizing the ultracold neutron source [1] at LANL. The experiment consists of loading the neutrons in a magneto-gravitational trap and counting the neutrons surviving the beta decay using a ¹⁰B-coated ZnS scintillator. The experiment so far has provided the most precise neutron lifetime in the world with a value of 877.75 ± 0.28_stat + 0.22/−0.16_syst s [2]. With UCNτ being upgraded to UCNτ+, the data set from the experiment (2020-2022) is being analyzed to get the latest neutron lifetime results. In this contribution, I will discuss the analysis methodology for the data and explain the role of various systematics in the measurement.