Storage of Ultracold Neutrons in the Magneto-Gravitational Trap of the UCNt Experiment
by Seppo Penttila, James Bowman, et al.
The UCNt experiment is designed to measure the lifetime tn of the free neutron by trapping ultracold neutrons (UCN) in a magneto-gravitational trap. An asymmetric bowl-shaped NdFeB magnet Halbach array confines low-field-seeking UCN within the apparatus, and a set of electromagnetic coils in a toroidal geometry provides a background “holding” field to eliminate depolarization-induced UCN loss caused by magnetic field nodes. We present a measurement of the storage time tstore of the trap by storing UCN for various times and counting the survivors. The data are consistent with a single exponential decay, and we find tstore = 860 ± 19 s, within 1s of current global averages for tn. The storage time with the holding field deactivated is found to be tstore = 470 ± 160 s; this decreased storage time is due to the loss of UCN, which undergo Majorana spin flips while being stored. We discuss plans to increase the statistical sensitivity of the measurement and investigate