Confidence regions for neutrino oscillation parameters from double-Chooz data

Abstract

In this work, an independent and detailed statistical analysis of the double-Chooz experiment is performed. To have a thorough understanding of the implications of the double-Chooz data on both oscillation parameters ${\sin }^2(2{\theta }_{13})$ and $\Delta m_{31}^2$, we decided to analyze the data corresponding to the Far detector, with no additional restriction. By doing this, confidence regions and best fit values are obtained for (${\sin }^2(2{\theta }_{13}),\Delta m_{31}^2$). This analysis yields an out-of-order $\Delta m_{31}^2$ minimum, which has already been mentioned in previous works, and it is corrected with the inclusion of additional restrictions. With such restrictions it is obtained that ${\sin }^2(2{\theta }_{13})=0.084_{-0.028}^{+0.030}$ and $\Delta m_{31}^2=2.444_{-0.215}^{+0.187}\times 10^{-3}$ eV${}^2$/c${}^4$. Our analysis allows us to study the effects of the so called "spectral bump" around 5 MeV, it is observed that a variation of this spectral bump may be able to move the $\Delta m_{31}^2$ best fit value, in such a way that $\Delta m_{31}^2$ takes the order of magnitude of the MINOS value. Finally, and with the intention of understanding the effects of the preliminary Near detector data, we performed two different analyses, aiming to eliminate the effects of the energy bump. As a consequence, it is found that unlike the Far Detector analysis, the Near detector data may be able to fully determine both oscillation parameters by itself, resulting in, ${\sin }^2(2{\theta }_{13})=0.095\pm 0.053$ and $\Delta m_{31}^2=2.63_{-1.15}^{+0.98}\times 10^{-3}{\text{eV}}^2/{\text{c}}^4$. The later analyses represent an improvement with respect to previous works, where additional constraints for $\Delta m_{31}^2$ were necessary.

arXiv comment11 pages, 2 b/n figure, 5 color figures, 6 tables

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