In the Standard Model, there are seven experimentally determined constants pertaining to neutrinos - the three neutrino masses and the four parameters of the PMNS matrix that governs neutrino oscillations. Progress has been made recently in determining some of those parameters:
We present an up-to-date global analysis of data coming from neutrino oscillation and non-oscillation experiments, as available in April 2018, within the standard framework including three massive and mixed neutrinos. We discuss in detail the status of the three-neutrino (3nu) mass-mixing parameters, both known and unknown. Concerning the latter, we find that:
normal ordering (NO) is favored over inverted ordering (IO) at 3sigma level;
the Dirac CP phase is constrained within ~15% (~9%) uncertainty in NO (IO) around nearly-maximal CP-violating values;
the octant of the largest mixing angle and the absolute neutrino masses remain undetermined.
We briefly comment on other unknowns related to theoretical and experimental uncertainties (within 3nu) or possible new states and interactions (beyond 3nu).
F. Capozzi, E. Lisi, A. Marrone, A. Palazzo "Current unknowns in the three neutrino framework" (April 25, 2018).
In addition, the differences between the masses of the three neutrino masses are all known to reasonable accuracy, and that combined with the lower bound that none of the neutrino masses can be less than zero, and the upper bounds provided by cosmic background radiation experiments, actually places moderately strong limitations on each of the possible absolute neutrino masses, although all are known only to order of magnitude precision.