Global fit to three neutrino mixing: critical look at present precision

TL;DR

This work delivers a comprehensive global analysis of neutrino oscillations in the 3ν framework by integrating solar, atmospheric, reactor, and accelerator data, explicitly addressing $\Delta m^2_{21}$, $|\Delta m^2_{31}|$, $\theta_{12}$, $\theta_{23}$, $\theta_{13}$, and $\delta_{\rm CP}$ and their impact on the leptonic mixing matrix $|U|$ in both normal and inverted orderings. It leverages two reactor-flux scenarios to study flux-systematics and employs beam–reactor–atmospheric interplay to probe $\theta_{23}$ and $\delta_{CP}$, including the mass-ordering ambiguity. The analysis finds $\theta_{13}$ to be clearly nonzero with $\Delta\chi^2 \approx 100$, while $\theta_{23}$ favors a nonmaximal value at about $1.7$–$2\sigma$ depending on ordering; octant and $\delta_{CP}$ remain weakly constrained, with NO and IO both providing good fits. Atmospheric data prove crucial for lifting degeneracies and enhancing CP sensitivity when combined with reactor data, illustrating the value of a multi-channel global fit for informing neutrino mass models and guiding future experiments with improved flux control and near detectors.

Abstract

We present an up-to-date global analysis of solar, atmospheric, reactor, and accelerator neutrino data in the framework of three-neutrino oscillations. We provide results on the determination of theta_13 from global data and discuss the dependence on the choice of reactor fluxes. We study in detail the statistical significance of a possible deviation of theta_23 from maximal mixing, the determination of its octant, the ordering of the mass states, and the sensitivity to the CP violating phase, and discuss the role of various complementary data sets in those respects.

Figures (7)

• Figure 1: Global $3\nu$ oscillation analysis. Each panels shows two-dimensional projection of the allowed six-dimensional region after marginalization with respect to the undisplayed parameters. The different contours correspond to the two-dimensional allowed regions at $1\sigma$, 90%, $2\sigma$, 99% and $3\sigma$ CL (2 dof). Results for different assumptions concerning the analysis of data from reactor experiments are shown: full regions correspond to analysis with the normalization of reactor fluxes left free and data from short-baseline (less than 100 m) reactor experiments are included. For void regions short-baseline reactor data are not included but reactor fluxes as predicted in Huber:2011wv are assumed. Note that as atmospheric mass-squared splitting we use $\Delta m^2_{31}$ for NO and $\Delta m^2_{32}$ for IO.
• Figure 2: Global $3\nu$ oscillation analysis. The red (blue) curves are for Normal (Inverted) Ordering. Results for different assumptions concerning the analysis of data from reactor experiments are shown: for solid curves the normalization of reactor fluxes is left free and data from short-baseline (less than 100 m) reactor experiments are included. For dashed curves short-baseline data are not included but reactor fluxes as predicted in Huber:2011wv are assumed. Note that as atmospheric mass-squared splitting we use $\Delta m^2_{31}$ for NO and $\Delta m^2_{32}$ for IO.
• Figure 3: Upper: $\Delta\chi^2$ as a function of $\sin^2\theta_{13}$ for the different reactor experiments and different assumptions on the fluxes as labeled in the figure. In this figure we fix $\Delta m^2_{31}=2.47\times 10^{-3}~\text{eV}^2$. Lower: contours in the plane of $\sin^2\theta_{13}$ and the flux normalization $f_\text{flux}$. Full regions (lines) correspond to analysis with (without) including the RSBL experiments.
• Figure 4: $3\sigma$ allowed regions in the plane of $|\Delta m^2_{31}|$ and $\sin^2\theta_{13}$ for different combinations of the reactor experiments. The region labeled "ALL REACTORS" does not include Kamland.
• Figure 5: Dependence of $\Delta\chi^2$ on $\sin^2\theta_{13}$ for the different data samples and assumptions as labeled in the figure and the corresponding $1\sigma$ ranges.