Searching for ¹³⁶Xe Double-Beta Decay to Excited States with Machine Learning

The observation of neutrinoless double beta decay (0νββ) would confirm that neutrinos are Majorana particles, their own antiparticles. 0νββ would also provide insight into the nature of neutrino mass and matter-antimatter asymmetry in the early universe. The KamLAND-ZEN experiment, located in Kamioka, Japan, is a liquid scintillator calorimeter detector searching for neutrinoless double-beta decay in ¹³⁶Xe nuclei. With over a kiloton-year of exposure to ¹³⁶Xe, KamLAND-Zen has set the world-leading limit on the Majorana neutrino mass. However, there remain large uncertainties in the nuclear matrix elements that govern the relationship between double-beta decay halflife and the Majorana neutrino mass. Further observations of SM two-neutrino double beta decay to excited states of the daughter nucleus would help the determination of these nuclear matrix elements. In this talk, I will present preliminary results for the search for ¹³⁶Xe double-beta decay to excited states of Barium, and the improvement in sensitivity gained from employing the spherical convolutional-LSTM ML model, KamNet.