The UCNτ measurement of the free neutron lifetime: overview and status report

The UCNτ experiment measures the mean decay lifetime of the free neutron. Ultracold neutrons (UCN) from the Los Alamos ultracold neutron facility are loaded into an asymmetric trap wherein they are confined by gravity and an array of permanent magnets, and, after varying storage times, the surviving UCN are counted in-situ. The recent installation of a preconditioning storage volume has improved the ability to normalize the number of neutrons loaded into the trap for each data run by partially removing the effect of the pulsed nature of the Los Alamos UCN source. The experiment has completed acquiring production data during two annual accelerator run cycles, leading to a statistical uncertainty on the neutron lifetime well below 0.5 s. We will present the status of the analysis and the ongoing multiyear production run.