Determine the absolute neutrino mass scale
Determine the absolute mass scale of neutrinos, i.e., the overall magnitude of neutrino masses independent of mixing and ordering, which remains unresolved in particle physics and for which neutrinoless double-beta decay half-life measurements could provide critical insights.
References
The half-life of this process ($T{0\nu}_{1/2}$) could provide insights into the absolute mass scale of neutrinos, which is still an unsolved issue in particle physics.
— Simultaneous Measurement of Half-Life and Spectral Shape of $^{115}$In $β$-decay with an Indium Iodide Cryogenic Calorimeter
(2401.16059 - Pagnanini et al., 29 Jan 2024) in Introduction, first paragraph (p. 1)