Systematic effects in a next-generation magnetic trap-based neutron lifetime measurement

The UCNτ2 experiment at the Los Alamos Neutron Science Center (LANSCE) will measure the free neutron lifetime τ_n to the 0.01% level, leveraging techniques developed for the ongoing UCNτ effort. The current experiment employs a ∼1 T NdFeB magnet array to trap ultracold neutrons (UCN) from the LANSCE UCN source. UCN are filled into the trap, stored for hundreds of seconds, and the surviving neutrons are counted. We have developed several techniques to study and mitigate systematic effects related to determining the relative number of UCN per fill ("normalization"), removing untrappable high energy UCN ("cleaning"), and potential time-dependent modulations of the trapping potential ("heating"). The next-generation effort will use a superconducting magnetic trap with larger volume and at least two-fold greater magnetic field strength to more efficiently use the LANSCE source and improve statistical sensitivity. A successful experiment will require improved techniques for normalization, cleaning, and heating-related effects. Here we outline the UCN detector technology, neutron tracking simulations, and data-driven systematic studies needed to measure τ_n to unprecedented precision.