Effect of Detector Coincidence Criteria on a High Precision Measurement of the Neutron Lifetime

Abstract

The UCNtau collaboration is working to measure the mean lifetime of a free neutron to 0.1s using very low energy “ultracold” neutrons (UCN). Achieving such high precision is important in a variety of low-energy tests for new physics. A density of UCN is produced in the Los Alamos solid-D2 super-thermal source and is then polarized and guided to a magneto-gravitational trap. The UCN that have high enough energy to escape the trapping potential are cleaned out, and the remaining neutrons are left to decay for two time intervals, a short and long holding time. The difference in the two holding times, along with the normalized number of neutrons left in the trap at the end of the holding periods, are used to calculate the average lifetime of the neutrons in the trap. The neutrons are detected using a newly-developed in situ active detector that observes light from a B-coated ZnS scintillation screen via a pair of photomultiplier tubes . Over the past year I have been doing an in depth analysis of the 2015-2016 data set and will present preliminary blinded results from my ongoing analysis.