Material Depolarization of ultracold neutrons in collision with material guide tubes

Abstract

Ultracold Neutrons are defined as neutrons with a very low energy, ~100neV, whose behavior differs from common neutrons. Due to their neutral net charge, neutrons normally do not interact with matter and simply pass through materials, but ultracold neutrons will collide with materials and be deflected, acting similar to magnetic bouncing balls(due to their magnetic moment).  When colliding with materials, ultracold neutrons have a small probability of undergoing a spin flip. In experiments like UCNtau and other beta-decay experiments, the behavior of UCN populations is paramount for increasing the statistics. The Los Alamos National Lab UCN team performed an experiment in which ultracold neutrons were polarized using a 6T longitudinal magnetic field. When encountering the field, only neutrons of a certain spin state (High field-seeking) are able to pass through the field. The ones that can are then held within a material guide tube within a magnetic holding field. They are contained in the guide for a variable time interval to allow for depolarization, then a shutter is opened and the UCN are counted. The ratio of the initial population to the population detected as a function of time can be used to calculate the rate of depolarization per bounce of an ultracold neutron for a given material. My work consisted of analyzing the raw data from this experiment using the analysis framework ROOT.  Raw data files were converted into histograms and summed to produce an arrival time histogram, from which observables were extracted for depolarization calculations.