Extracting Majorana Properties in the Throat of Neutrinoless Double Beta Decay

TL;DR

This paper investigates how future neutrinoless double beta decay experiments can reveal Majorana neutrino properties, especially CP phases and mass hierarchy, by analyzing non-observation limits and combining data from reactor neutrino experiments.

Contribution

It demonstrates how strong limits on neutrinoless double beta decay can determine Majorana CP phases and neutrino mass parameters, especially when contributions partly cancel.

Findings

Majorana CP phases can be precisely determined from decay limits.

Complementary measurements from JUNO/RENO-50 improve predictions.

Future experiments need to reach sensitivities around 1 meV for effective mass.

Abstract

Assuming that neutrinos are Majorana particles, we explore what information can be inferred from future strong limits (i.e. non-observation) for neutrinoless double beta decay. Specifically we consider the case where the mass hierarchy is normal and the different contributions to the effective mass $\langle m \rangle_{ee}$ partly cancel. We discuss how this fixes the two Majorana CP phases simultaneously from the Majorana Triangle and how it limits the lightest neutrino mass $m_1$ within a narrow window. The two Majorana CP phases are in this case even better determined than in the usual case for larger $\langle m \rangle_{ee}$. We show that the uncertainty in these predictions can be significantly reduced by the complementary measurement of reactor neutrino experiments, especially the medium baseline version JUNO/RENO-50. We also estimate the necessary precision on $\langle m \rangle_{ee}$ to infer non-trivial Majorana CP phases and the upper limit $\langle m \rangle_{ee} \lesssim 1\,\mbox{meV}$ sets a target for the design of future neutrinoless double beta decay experiments.