Measurement of a New Half-Lifetime Lower Limit for Neutrinoless Double-Beta Decay in Xe-136 Using the Full EXO-200 Phase 1 Data Set and Improvements to Barium Tagging for nEXO [thesis]

Warren Cree
Several major experiments are currently underway attempting to observe neutrinoless double-beta decay (0νββ). This decay is of interest in the physics community because a measurement of it's half-life would lead directly to a measurement of the effective Majorana-neutrino mass and therefore the absolute neutrino mass scale. Furthermore, the decay is interesting because it demonstrates non-conservation of lepton number and the Majorana nature of neutrinos, two features which are not forbidden by
more » ... re not forbidden by the Standard Model but have not been observed experimentally. This work focuses on improvements to two such experiments, EXO-200 and it's successor, nEXO. An improved analysis technique for EXO-200 is developed using Boosted Decision Trees, leading to a 12% improvement to sensitivity and a 13% improvement to the 0νββ half-life lower limit. Furthermore, improvements are made to the nEXO barium tagging system producing a 50% improvement in signal-to-background ratio as well as some improvement to the continuous excitation technique. ii
doi:10.22215/etd/2017-12161 fatcat:yzuv7bmntjgube3abmznr2pgce