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