Hints of ${\theta }_{13}>0$ from Global Neutrino Data Analysis

Nailing down the unknown neutrino mixing angle ${\theta }_{13}$ is one of the most important goals in current lepton physics. In this context, we perform a global analysis of neutrino oscillation data, focusing on ${\theta }_{13}$, and including recent results [Neutrino 2008, Proceedings of the XXIII International Conference on Neutrino Physics and Astrophysics, Christchurch, New Zealand, 2008 (unpublished)]. We discuss two converging hints of ${\theta }_{13}>0$, each at the level of $\sim 1\sigma$: an older one coming from atmospheric neutrino data, and a newer one coming from the combination of solar and long-baseline reactor neutrino data. Their combination provides the global estimate ${sin}^2{\theta }_{13}=0.016\pm 0.010(1\sigma )$, implying a preference for ${\theta }_{13}>0$ with non-negligible statistical significance ($\sim 90\%$ C.L.). We discuss possible refinements of the experimental data analyses, which might sharpen such intriguing indications.

Figure 1

Allowed regions in the plane (${sin}^2{\theta }_{12}$, ${sin}^2{\theta }_{13}$): contours at $1\sigma$ (dotted) and $2\sigma$ (solid). Left and middle panels: solar (S) and KamLAND (K) data, both separately (left) and in combination (middle). In the left panel, the S contours are obtained by marginalizing the $\delta m^2$ parameter as constrained by KamLAND. Right panel: All data.

Figure 2

Global $\nu$ oscillation analysis: Allowed $1\sigma$ ranges of ${sin}^2{\theta }_{13}$ from different input data.