UCNτ+: Higher Precision on the Neutron Lifetime through Improved Loading of the UCNτ Magneto-Gravitational Trap*

UCNτ+ is an upgrade underway to increase the sensitivity of the UCNτ experiment at the Los Alamos Neutron Science Center.  Neutron decay measurements determine the weak coupling constants for the nucleon which are free from nuclear structure corrections, providing powerful tests for beyond standard model effects and strongly motivating experimental progress.  The most precise measurement of the free neutron lifetime was recently reported by the UCNτ collaboration, with the planned UCNτ+  upgrade promising a factor of two or more improvement over current UCNτ precision. The UCNτ project utilizes the existing UCNτ magneto-gravitational trap, introducing an adiabatic transport system to improve the number of loaded ultracold neutrons (UCN) and implementing a higher rate (in situ) UCN detector.  An introduction to the UCNτ+ project is presented, highlighting Monte-Carlo simulations of a conceptual design for the adiabatic transport system.  Aspects of the transport strategy and the impact of transport parameters such as guide specularity, guide loss per bounce, and gaps between transport elements, are studied to understand their effects on the final detected UCN population. We also characterize the issue of depolarization while loading the trap.