Towards a Spectral Shape Measurement of the Decay of ¹³⁷Xe to the (5/2+) ¹³⁷Cs State

EXO-200 was the first kilomole-scale neutrinoless double beta decay (0νββ) experiment. It operated a single-phase liquid xenon time projection chamber (TPC) with ~150 kg of xenon enriched to 80% in the isotope 136 and made the first observation of the 2νββ decay of ¹³⁶Xe to the ground state of ¹³⁶Ba. In late 2018, an AmBe neutron source was deployed as part of an end-of-run detector calibration which produced ¹³⁷Xe inside the detector by neutron capture on ¹³⁶Xe. ¹³⁷Xe beta decays via two modes: to the ground state and the first excited state of ¹³⁷Cs. Combined, the measurement of the spectral shape of the decays can inform on the effective value of the axial coupling constant, g_A, in these nuclei. EXO-200 measured the β⁻ decay of ¹³⁷Xe to the ground state of ¹³⁷Cs in 2020. This talk will go over the methodology behind the ongoing measurement of the beta decay of ¹³⁷Xe to the 5/2+ excited state of ¹³⁷Cs, which is accompanied by the emission of a 455 keV γ ray. Progress on calibrating both the ionization charge and scintillation light signals to measure this topologically distributed signal will be presented.