Majorana neutrino mass constraints in the landscape of nuclear matrix elements

Abstract

We discuss up-to-date constraints on the Majorana neutrino mass mββ from neutrinoless double beta decay (0νββ) searches in experiments using different isotopes: KamLAND-Zen and EXO (Xe136), GERDA and MAJORANA (Ge76) and CUORE (Te130). Best fits and upper bounds on mββ are explored in the general landscape of nuclear matrix elements (NME), as well as for specific NME values obtained in representative nuclear models. By approximating the likelihood of 0νββ signals through quadratic forms, the analysis of separate and combined isotope data becomes exceedingly simple, and allows us to clarify various aspects of multi-isotope data combinations. In particular, we analyze the relative impact of different data in setting upper bounds on mββ, as well as the conditions leading to nonzero mββ at best fit, for variable values of the NMEs. Detailed results on mββ from various combinations of data are reported in graphical and numerical form. Implications for future 0νββ data analyses and NME calculations are briefly discussed.