2 research outputs found
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Double Chooz ? 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 (?1, ?2, ?3) are mixtures of their flavour eigenstates (?e, ?µ, ?t). The oscillations between different flavour eigenstates are described by three mixing angles (?12, ?23, ?13), two differences of the squared neutrino masses of the ?2/?1 and ?3/?1 pairs and a charge conjugation parity symmetry violating phase dCP. The Double Chooz experiment, located near the Chooz Electricité de France reactors, measures the oscillation parameter ?13 using reactor neutrinos. Here, the Double Chooz collaboration reports the measurement of the mixing angle ?13 with the new total neutron capture detection technique from the full data set, yielding sin2(2?13) = 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 = (5.71 ± 0.06) × 10-43 cm2 per fission, and reports an empirical model of the distortion in the reactor neutrino spectrum
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Measurement of ?13 in Double Chooz using neutron captures on hydrogen with novel background rejection techniques
The Double Chooz collaboration presents a measurement of the neutrino mixing angle ?13 using reactor ?e¯ (Formula presented.) observed via the inverse beta decay reaction in which the neutron is captured on hydrogen. This measurement is based on 462.72 live days data, approximately twice as much data as in the previous such analysis, collected with a detector positioned at an average distance of 1050 m from two reactor cores. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties. Accidental coincidences, the dominant background in this analysis, are suppressed by more than an order of magnitude with respect to our previous publication by a multi-variate analysis. These improvements demonstrate the capability of precise measurement of reactor ?e¯ (Formula presented.) without gadolinium loading. Spectral distortions from the ?e¯ (Formula presented.) reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin2 2?13 = 0.095- 0.039+ 0.038 (stat+syst) is obtained from a fit to the observed event rate as a function of the reactor power, a method insensitive to the energy spectrum shape. A simultaneous fit of the hydrogen capture events and of the gadolinium capture events yields a measurement of sin2 2?13 = 0.088 ± 0.033(stat+syst)