Reactor and Antineutrino Spectrum Calculations for the Double Chooz First Phase Results

The Double Chooz reactor oscillation experiment is designed to search for a non-vanishing value of the mixing angle θ13. For the first phase of the experiment with only the far detector running, the reactor electron antineutrino flux is normalized via reactor simulation. For this first phase and from its last results, Double Chooz observed an evidence for a reactor electron antineutrino disappearance. In 227.93 days of far detector live time, we obtained . This result excludes the no-oscillation hypothesis at 99.8% CL.