Abstract:
Among ongoing reactor-based experiments, Double Chooz is unique in obtaining data when the reactor cores are brought down for maintenance. These reactor-off data allow for a clean measurement of the backgrounds of the experiment, thus being of uppermost importance for the theta13 oscillation analysis. While the oscillation results published by the collaboration in 2011 and 2012 rely on background models derived from reactor-on data, in this talk we present an independent study based on the handle provided by 7.53 days of reactor-off data. A global fit to both theta13 and the total background is performed by analyzing the observed neutrino rate as a function of the non-oscillated expected rate for different reactor power conditions. The result presented in this talk is fully consistent with the one already published by Double Chooz. As they both yield almost the same precision, this work stands as a prove of the reliability of the background estimates and the oscillation analysis of the experiment.

Abstract:
Precise measurement of the neutrino mixing angle $\theta_{13}$ is the primary goal of the Double Chooz Experiment (DC), which is located in Chooz, France. The inverse beta decay process provides a unique signature of reactor anti-neutrino interactions, giving prompt signals from positron annihilation and delayed signals from neutron capture by either Gadolinium (Gd) or Hydrogen (H). This paper is dedicated to the latest nH analysis in Double Chooz. Typically, The Gd analysis is primary since fewer background events are involved. However, with accurate estimates of backgrounds and a precise reconstruction of energy, the nH analysis gives a powerful independent measurement of $\theta_{13}$.

Abstract:
We discuss the potential of the proposed Double Chooz reactor experiment to measure the neutrino mixing angle $\sin^2 2\theta_{13}$. We especially consider systematical uncertainties and their partial cancellation in a near and far detector operation, and we discuss implications of a delayed near detector startup. Furthermore, we introduce Triple Chooz, which is a possible upgrade scenario assuming a second, larger far detector, which could start data taking in an existing cavern five years after the first far detector. We review the role of the Chooz reactor experiments in the global context of future neutrino beam experiments. We find that both Double Chooz and Triple Chooz can play a leading role in the search for a finite value of $\sin^2 2\theta_{13}$. Double Chooz could achieve a sensitivity limit of $\sim 2 \cdot 10^{-2}$ at the 90%~confidence level after 5~years while the Triple Chooz setup could give a sensitivity below $10^{-2}$.

Abstract:
The Double-Chooz experiment goal is to search for a non-vanishing value of the Theta13 neutrino mixing angle. This is the last step to accomplish prior moving towards a new era of precision measurements in the lepton sector. The current best constraint on the third mixing angle comes from the CHOOZ reactor neutrino experiment $\sin(2\theta_{13})^{2}<0.2$ (90% C.L., $\Delta m_{atm}^{2}=2.0$ eV$^{2}$). Double-Chooz will explore the range of $\sin(2\theta_{13})^{2}$ from 0.2 to 0.03-0.02, within three years of data taking. The improvement of the CHOOZ result requires an increase in the statistics, a reduction of the systematic error below one percent, and a careful control of the backgrounds. Therefore, Double-Chooz will use two identical detectors, one at 150 m and another at 1.05 km distance from the Chooz nuclear cores. In addition, we will to use the near detector as a ``state of the art'' prototype to investigate the potential of neutrinos for monitoring the civil nuclear power plants. The plan is to start operation with two detectors in 2008, and to reach a sensitivity sin$^{2}$$(2\theta_{13})$ of 0.05 in 2009, and 0.03-0.02 in 2011.

Abstract:
The Double Chooz experiment is the first of the next wave of reactor experiments searching for a non-vanishing value of the mixing angle theta_13. The experimental concept and detector design are presented, and the most pertinent backgrounds are discussed. Operation of the far detector is expected to begin by the end of 2009. Installation of the near detector will occur in 2010. Double Chooz has the capacity to measure sin^2(2theta_13) to 3 sigma if sin^2(2theta_13) >0.05 or exclude sin^2 (2theta_13) down to 0.03 at 90% for Delta m_31^2 = 2.5 x 10^-3 eV^2 with three years of data with both near and far detectors.

Abstract:
The latest results from the Double Chooz experiment on the neutrino mixing angle $\theta_{13}$ are presented. A detector located at an average distance of 1050 m from the two reactor cores of the Chooz nuclear power plant has accumulated a live time of 467.90 days, corresponding to an exposure of 66.5 GW-ton-year (reactor power $\times$ detector mass $\times$ live time). A revised analysis has boosted the signal efficiency and reduced the backgrounds and systematic uncertainties compared to previous publications, paving the way for the two detector phase. The measured $\sin^2 2\theta_{13} = 0.090^{+0.032}_{-0.029}$ is extracted from a fit to the energy spectrum. A deviation from the prediction above a visible energy of 4 MeV is found, being consistent with an unaccounted reactor flux effect, which does not affect the $\theta_{13}$ result. A consistent value of $\theta_{13}$ is measured in a rate-only fit to the number of observed candidates as a function of the reactor power, confirming the robustness of the result.

Abstract:
The Double Chooz reactor neutrino experiment will be the next detector to search for a non vanishing theta13 mixing angle with unprecedented sensitivity, which might open the way to unveiling CP violation in the leptonic sector. The measurement of this angle will be based in a precise comparison of the antineutrino spectrum at two identical detectors located at different distances from the Chooz nuclear reactor cores in France. Double Chooz is particularly attractive because of its capability to measure sin2(2theta13) to 3 sigmas if sin2(2theta13) > 0.05 or to exclude sin2(2theta13) down to 0.03 at 90% C.L. for Dm2 = 2.5 x 10-3 eV2 in three years of data taking with both detectors. The construction of the far detector starts in 2008 and the first neutrino results are expected in 2009. The current status of the experiment, its physics potential and design and expected performance of the detector are reviewed.

Abstract:
The oscillation results published by the Double Chooz collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle $\theta_{13}$ by including 7.53 days of reactor-off data. A global fit of the observed neutrino rates for different reactor power conditions is performed, yielding a measurement of both $\theta_{13}$ and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields $\sin^2(2\theta_{13})=$ 0.102 $\pm$ 0.028(stat.) $\pm$ 0.033(syst.). The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of $\theta_{13}$ that does not depend on a background model.

Abstract:
We investigate the possible effects of short-baseline antinu_e disappearance implied by the reactor antineutrino anomaly on the Double-Chooz determination of theta_{13} through the normalization of the initial antineutrino flux with the Bugey-4 measurement. We show that the effects are negligible and the value of theta_{13} obtained by the Double-Chooz collaboration is accurate only if Delta m^2_{41} is larger than about 3 eV^2. For smaller values of Delta m^2_{41} the short-baseline oscillations are not fully averaged at Bugey-4 and the uncertainties due to the reactor antineutrino anomaly can be of the same order of magnitude of the intrinsic Double-Chooz uncertainties.

Abstract:
Double Chooz is a reactor neutrino experiment which investigates the last neutrino mixing angle; theta-13. It is necessary to measure reactor neutrino disappearance with precision 1% or better to detect finite value of theta-13. This requirement is the most strict compared to other reactor neutrino experiments performed so far. The Double Chooz experiment makes use of a number of techniques to reduce the possible errors to achieve the sensitivity. The detector is now under construction and it is expected to take first neutrino data in 2009 and to measure sin^22theta-13 with a sensitivity of 0.03 (90%C.L.) In this proceedings, the technical concepts of Double Chooz detector are explained stressing on how it copes with the systematic errors.