Tau2: A next generation neutron lifetime experiment based on UCN$\tau $

The UCN$\tau $ experiment measures the free neutron lifetime by in situ counting of surviving ultracold neutrons (UCNs) after different storage times in an asymmetric magneto-gravitational storage volume.~ This experiment has acquired sufficient data for a measurement of the neutron lifetime with a statistical uncertainty of about 0.3 s and has demonstrated a systematic uncertainty of 0.28 s; it is expected to ultimately reach a total uncertainty of about 0.2 s, limited primarily by the efficiency with which UCN$\tau $ utilizes the neutrons supplied by the Los Alamos UCN facility.~ In this talk, we will describe the conceptual Tau2 experiment, which is intended to use the techniques learned during the UCN$\tau $ experiment to minimize systematic uncertainties while maximizing the statistical reach possible with UCNs supplied by the Los Alamos source.~ Replacing the permanent magnet-based trap of UCN$\tau $ with a larger volume superconducting trap is expected to enable improving the total uncertainty on the neutron lifetime to 0.1 s and beyond, permitting investigation of the weak nuclear force, when taken with precision beta decay correlation experiments, with physics reach comparable to LHC-based high energy experiments.