How many neutrinoless decays do you need to identify the physics?

When neutrinoless double-beta decay occurs, the energies and angles of the two ejected electrons encode which beyond-Standard-Model physics caused it. The authors show that you need only ~10 events to reach discovery-level confidence about the mechanism if backgrounds are clean, and ~25 with realistic detector noise—far fewer than conventionally assumed. This validates building expensive tracking detectors for next-generation experiments, even those expecting only handful of signals.