2020 Global reassessment of the neutrino oscillation picture

TL;DR

This paper provides an updated global analysis of neutrino oscillation data, refining measurements of mixing angles, mass differences, and the CP-violating phase, and assesses the neutrino mass ordering with improved statistical significance.

Contribution

It offers the most recent comprehensive global fit of neutrino oscillation parameters incorporating new experimental data and compares Bayesian and frequentist approaches for robustness.

Findings

Normal mass ordering is mildly preferred at 2.5σ.

Best-fit CP phase δ is around 1.08π for normal ordering.

Upper limits on total neutrino mass are established from cosmological data.

Abstract

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, we give updated analyses of DeepCore and SNO data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NO$\nu$A measurements. These new analyses result in more accurate measurements of $\theta_{13}$, $\theta_{12}$, $\Delta m_{21}^2$ and $|\Delta m_{31}^2|$. The best fit value for the atmospheric angle $\theta_{23}$ lies in the second octant, but first octant solutions remain allowed at $\sim2.4\sigma$. Regarding CP violation measurements, the preferred value of $\delta$ we obtain is 1.08$\pi$ (1.58$\pi$) for normal (inverted) neutrino mass ordering. The global analysis prefers normal neutrino mass ordering with 2.5$\sigma$. This preference is milder than the one found in previous global analyses. The new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of $2.00\sigma$. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to $2.68\sigma$ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference, namely $2.70\sigma$. This very same cosmological data set provides $2\sigma$ upper limits on the total neutrino mass corresponding to $\sum\nu<0.12$ ($0.15$)~eV for normal (inverted) neutrino mass ordering.