Statistical sensitivity of neutrinoless double-beta decay exchange mechanism discrimination by tracking experiments

TL;DR

Reconstruction of electron energies and angles in neutrinoless double-beta decay can effectively discriminate underlying mechanisms with surprisingly few events, even considering realistic uncertainties.

Contribution

Demonstrates that mechanism discrimination is possible with minimal events, challenging the belief that high statistics are necessary.

Findings

Discrimination at 1σ level with a few events.

3σ discovery with about 10 events.

Realistic uncertainties increase event requirement to ~25.

Abstract

Reconstruction of the individual energies and the opening angle between the electrons emitted in neutrinoless double-beta decay can probe the nature of the beyond-the-Standard-Model exchange mechanism that underlies the process. Although it is often stated that discrimination of the mechanism would require such measurements to be performed with high statistics, we show that this is not the case. If a single mechanism dominates the process, its discrimination at the 1$\sigma$ level is already achieved with just a few well-reconstructed events; only $\sim$10 such events are required to reach 3$\sigma$-level discovery sensitivity. In the presence of realistic reconstruction uncertainties, this requirement increases to $\sim$25 events, indicating that substantial discrimination power is retained as long as backgrounds remain small. We conclude that the pursuit of tracking detectors for exchange-mechanism discrimination remains valuable even for ``discovery-class'' experiments in which only a few signal counts are expected.