Measurement of systematic effects in the UCN$\tau$ experiment

One of the most important open questions about the fundamental properties of the neutron is the free neutron lifetime $(\tau_n).$ Experimental measures of $\tau_n$ can be broadly described in one of two ways: either a measurement using a cold neutron beam, or a measurement using ultracold neutrons (UCN) stored in a trap. There is a $\sim4\sigma$ discrepancy in measured $\tau_n$ between the two methods. The UCN$\tau$ experiment at Los Alamos Neutron Science Center fills an asymmetric magneto-gravitational trap with UCN, and then counts the surviving UCN after various holding times to measure $\tau_n.$ The UCN$\tau$ collaboration has published a systematic uncertainty of $^{+0.4}_{-0.2}$ s based on the analysis of our 2016-2017 data set. The effect of the depolarization of UCN is measured by varying the magnetic holding field magnitude. The effects of microphonic heating of trapped UCN and of insufficient cleaning of UCN with energies above the trapping potential are measured by detecting surviving high-energy UCN. The effect of phase space evolution of UCN is measured by comparing the time distributions of the surviving UCN after various holding times. We will present details of how these systematic effects are measured and projections of how they will be better constrained.