Global analysis of neutrino masses, mixings and phases: entering the era of leptonic CP violation searches

TL;DR

The paper presents a global analysis of neutrino oscillation data within a three-neutrino framework, incorporating the then-recent precise measurements of $\theta_{13}$ to explore correlations among $\theta_{13}$, $\theta_{23}$, and the CP phase $δ$. By combining LBL, solar, KamLAND, SBL reactor, and atmospheric data, it reveals covariances that lead to hints of $\theta_{23}<\pi/4$ and $δ\approx\pi$, with no strong distinction between normal and inverted mass hierarchies. The work also examines the implications for absolute masses, showing tight interdependencies among $m_β$, $m_{ββ}$, and $Σ$, while Majorana phases remain largely unconstrained. Overall, the findings guide future 3$\nu$ analyses and bear on upcoming experimental efforts to resolve the remaining neutrino mass and CP-violation questions, particularly through improved reactor-near/far data and atmospheric analyses.

Abstract

We perform a global analysis of neutrino oscillation data, including high-precision measurements of the neutrino mixing angle theta_13 at reactor experiments, which have confirmed previous indications in favor of theta_13>0. Recent data presented at the Neutrino 2012 Conference are also included. We focus on the correlations between theta_13 and the mixing angle theta_23, as well as between theta_13 and the neutrino CP-violation phase delta. We find interesting indications for theta_23< pi/4 and possible hints for delta ~ pi, with no significant difference between normal and inverted mass hierarchy.

Figures (4)

• Figure 1: Results of the analysis in the plane charted by ($\sin^2\theta_{13}, \,\sin^2\theta_{23}$), all other parameters being marginalized away. From left to right, the regions allowed at 1, 2 and $3\sigma$ refer to increasingly rich datasets: LBL+solar+KamLAND data (left panels), plus SBL reactor data (middle panels), plus SK atmospheric data (right panels). Best fits are marked by dots. A preference emerges for $\theta_{23}$ in the first octant in both normal hierarchy (NH, upper panels) and inverted hierarchy (IH, lower panels).
• Figure 2: Results of the analysis in the plane charted by ($\sin^2\theta_{13}, \,\delta$), all other parameters being marginalized away. From left to right, the regions allowed at 1, 2 and $3\sigma$ refer to increasingly rich datasets: LBL+solar+KamLAND data (left panels), plus SBL reactor data (middle panels), plus SK atmospheric data (right panels). A preference emerges for $\delta$ values around $\pi$ in both normal hierarchy (NH, upper panels) and inverted hierarchy (IH, lower panels).
• Figure 3: Results of the global analysis in terms of $N\sigma$ bounds on the six parameters governing $3\nu$ oscillations. Blue (solid) and red (dashed) curves refer to NH and IH, respectively.
• Figure 4: Constraints induced by oscillation data (at $2\sigma$ level) in the planes charted by any two among the absolute mass observables $m_\beta$ (effective electron neutrino mass), $m_{\beta\beta}$ (effective Majorana mass), and $\Sigma$ (sum of neutrino masses). Blue (red) bands refer to normal (inverted) hierarchy.