Confidence regions for neutrino oscillation parameters from double-Chooz data

In this work, an independent and detailed statistical analysis of the double-Chooz experiment is performed. In order to have a thorough understanding of the implications of the double-Chooz data on both oscillation parameters sin2(2θ13) and Δm312, we decided to analyze the data corresponding to the Far detector, with no additional restriction. This differs from previous analyses, which only aim to estimate the mixing angle θ13, without mentioning the effects on Δm312. By doing this, confidence regions and best fit values are obtained for (sin2(2θ13),Δm312). This analysis yields an out-of-order Δm312 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 sin2(2θ13)=0.084-0.028+0.030 and Δm312=2.444-0.215+0.187×10-3 eV2/c4. 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 Δm312 best fit value, in such a way that Δm312 takes the order of magnitude of the MINOS value. In other words, if we allow the variation of the spectral bump, then we may be able to determine both oscillation parameters using Far detector data only, with no further restrictions from other experiments. 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 sin2(2θ13)=0.095±0.053 and Δm312=2.63-1.15+0.98×10-3 eV2/c4. The later analyses represent an improvement with respect to previous works, where additional constraints for Δm312 were necessary.