EXO-200 uses an ultra low background time projection chamber filled with 110 kg of active enriched liquid xenon to search for neutrinoless double beta decay of 136Xe. Double beta decays of 136Xe to the ground state of 136Ba are the most abundant, but the transitions to excited states of the daughter 136Ba nucleus are also of interest. The lifetime of ββ2ν decay to the first 0+ excited state of the daughter nucleus is expected to be on the order of 1025 year, which may be reachable by EXO-200. The decay to the lowest 2+ excited state is energetically favored, but suppressed by additional phase space factors. A machine learning algorithm is used to improve multi-variable signal to background discrimination, and a lower limit to the lifetime of ββ2ν decay to the 0+ level was recently published with two years of EXO-200 data. I will present these results along with sensitivity estimates for transitions to other excited states of 136Ba, which make use of an optimization of the reconstruction methods to maintain signal efficiency.
Argonne Physics Division Seminar Schedule