Measurement of systematic effects in the UCNτ experiment

There have been various measurements of the free neutron lifetime (τ_n) using either cold neutron beams, or ultracold neutrons (UCN) stored in a trap.  There is a ∼4σ discrepancy in measured lifetimes between the two methods. The UCNτ experiment at Los Alamos Neutron Science Center uses an asymmetric magneto-gravitational trap to store UCN, and counts t­he UCN remaining in the trap after various holding times to measure τ_n. Analysis of our 2016-2017 data established a current limit for our systematic uncertainty of +0.4/-0.2 s. Some systematic effects that can change the measured τ_n are depolarization and microphonic heating of trapped UCN, insufficient cleaning of UCN with energies above the trapping potential, and phase space evolution of UCN during storage. The effect of depolarization is measured by changing the strength of the magnetic holding field, the effects of heating and insufficient cleaning are measured by detecting high-energy UCN, and the effect of phase space evolution is measured by comparing the time distributions of UCN after different holding times. We will present details of how these systematic uncertainties are measured and projections of how they will be better constrained.