Implications of the Super-K atmospheric data for the mixing angles $\theta_{13}$ and $\theta_{23}$

TL;DR

This paper analyzes recent Super-K atmospheric neutrino data combined with other experiments to refine the measurements of the neutrino mixing angles $ heta_{13}$ and $ heta_{23}$, considering Earth's matter effects and parameter correlations.

Contribution

It provides a detailed three-neutrino oscillation analysis with an exact Earth matter effect treatment, revealing asymmetric errors and parameter correlations for $ heta_{13}$ and $ heta_{23}$.

Findings

Asymmetric errors for $ heta_{13}$ and $ heta_{23}$ were found.

The lower bound on $ heta_{13}$ is set by CHOOZ, upper by Super-K data.

$ heta_{13}$ and $ heta_{23}$ are correlated, affecting their allowed regions.

Abstract

A three-neutrino analysis of oscillation data is performed using the recent, more finely binned Super-K oscillation data, together with the CHOOZ, K2K, and MINOS data. The solar parameters, $\Delta_{21}$ and $\theta_{12}$, are fixed from a recent analysis, and $\Delta_{32}$, $\theta_{13}$, and $\theta_{23}$ are varied. We utilize the full three-neutrino oscillation probability and an exact treatment of the Earth's MSW effect with a castle-wall density. By including terms linear in $\theta_{13}$ and $\varepsilon := \theta_{23} - \pi/4$, we find asymmetric errors for these parameters $\theta_{13}=-0.07^{+0.18}_{-0.11}$ and $\varepsilon=0.03^{+0.09}_{-0.15}$. For $\theta_{13}$, we see that the lower bound is primarily set by the CHOOZ experiment while the upper bound is determined by the low energy $e$-like events in the Super-K atmospheric data. We find that the parameters $\theta_{13}$ and $\varepsilon$ are correlated -- the preferred negative value of $\theta_{13}$ permits the preferred value of $\theta_{23}$ to be in the second octant, and the true value of $\theta_{13}$ affects the allowed region for $\theta_{23}$.