Preliminary Results from the UCNτ Experiment

There is currently a 4 σ  discrepancy between measurements of the neutron lifetime performed using cold neutron beams and those performed with ultracold neutron (UCN) storage vessels. The UCN τ  experiment uses an asymmetric magneto-gravitational UCN trap with {\it in situ} counting of surviving neutrons to measure the neutron lifetime. This design eliminates a major systematic of previous bottle experiments related to the loss of UCN on material trap walls and with unloading neutrons from the storage vessel. A new {\it in situ} detection system was used in the 2015-2016 run that was able to measure the population of surviving UCN at different heights in the trap, providing important information on spectral evolution. Understanding the behavior of quasi-bound UCN in a bottle experiment is essential to achieving a subsecond precision measurement of  τ n . We will present the preliminary results from the 2015-2016 data set and an update on the UCN τ  experiment.