Confidence regions for neutrino oscillation parameters from double-Chooz data

TL;DR

This paper performs a detailed statistical analysis of double-Chooz data to determine neutrino oscillation parameters, addressing spectral features and the impact of near detector data, resulting in improved parameter estimates.

Contribution

It introduces an independent analysis of double-Chooz data, correcting previous out-of-order minima and exploring effects of spectral bumps and near detector data on oscillation parameter estimation.

Findings

Best fit values: sin^2(2θ13)=0.084 and Δm^2_31≈2.44×10^{-3} eV^2

Near detector data can independently determine both parameters

Spectral bump variations influence Δm^2_31 estimates

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 $\Delta m^2_{31}$, 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 ($\sin^{2}(2\theta_{13}),\Delta m^2_{31}$). This analysis yields an out-of-order $\Delta m^2_{31}$ 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 $\Delta m^2_{31}=2.444^{+0.187}_{-0.215} \times 10^{-3}$ 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 $\Delta m^2_{31}$ best fit value, in such a way that $\Delta m^2_{31}$ 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 $\Delta m^{2}_{31} = 2.63^{+0.98}_{-1.15} \times 10^{-3} \text{eV}^2 / \text{c}^4$. The later analyses represent an improvement with respect to previous works, where additional constraints for $\Delta m^2_{31}$ were necessary.