Tau2: A next generation neutron lifetime experiment based on UCN&tau*

The UCNτ 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.  It has acquired sufficient data to measure 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 UCNτ utilizes the neutrons from the Los Alamos UCN facility.  In this talk, we will describe the conceptual Tau2 experiment, which is intended to use UCNτ techniques to minimize systematic uncertainties while maximizing the statistical reach possible with UCNs supplied by Los Alamos.  Replacing the permanent magnet-based trap of UCNτ 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.