Double Chooz θ ₁₃ measurement via total neutron capture detection

Neutrinos were assumed to be massless particles until the discovery of the neutrino oscillation process. This phenomenon indicates that the neutrinos have non-zero masses and the mass eigenstates (ν₁, ν₂, ν₃) are mixtures of their flavour eigenstates (ν_e, ν_μ, ν_τ). The oscillations between different flavour eigenstates are described by three mixing angles (θ₁₂, θ₂₃, θ₁₃), two differences of the squared neutrino masses of the ν₂/ν₁ and ν₃/ν₁ pairs and a charge conjugation parity symmetry violating phase δ_CP. The Double Chooz experiment, located near the Chooz Electricité de France reactors, measures the oscillation parameter θ₁₃ using reactor neutrinos. Here, the Double Chooz collaboration reports the measurement of the mixing angle θ₁₃ with the new total neutron capture detection technique from the full data set, yielding sin²(2θ₁₃) = 0.105 ± 0.014. This measurement exploits the multidetector configuration, the isoflux baseline and data recorded when the reactors were switched off. In addition to the neutrino mixing angle measurement, Double Chooz provides a precise measurement of the reactor neutrino flux, given by the mean cross-section per fission 〈σ_f〉 = (5.71 ± 0.06) × 10⁻⁴³ cm² per fission, and reports an empirical model of the distortion in the reactor neutrino spectrum.