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Register a new userImproved measurements of the neutrino mixing angle $theta_{13}$ with the Double Chooz detector
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The Double Chooz experiment presents improved measurements of the neutrino mixing angle $theta_{13}$ using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the $bar u_{e}$ signal has increased. The value of $theta_{13}$ is measured to be $sin^{2}2theta_{13} = 0.090 ^{+0.032}_{-0.029}$ from a fit to the observed energy spectrum. Deviations from the reactor $bar u_{e}$ prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of $theta_{13}$ is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the $theta_{13}$ measurement despite the observed distortion.
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The Double Chooz Reactor Neutrino Experiment in France plans to quickly measure the neutrino mixing angle theta-13, or limit it to sin^2 2-theta_13 less than 0.025. The physics reach, experimental site, detector structures, scintillator, photodetection, electronics, calibration and simulations are described. The possibility of using Double Chooz to explore the possible use of a antineutrino detector for non-proliferation goals is also presented.
The establishment of the neutrino oscillations phenomenon as a solution to both solar and atmospheric neutrino anomalies had two consequences: a new oscillation mode, labelled $mathbf{theta_{13}}$, and the possibility to observe CP violation, if $mathbf{theta_{13}}$ was sizeable. CP violation implies that neutrino oscillations behave differently for neutrinos and anti-neutrinos -- a rare fundamental phenomenon key for our understanding of the Universe. The experimental demonstration of $mathbf{theta_{13}}$ has aided the completion of a quest lasting half a century. The best $mathbf{theta_{13}}$ knowledge is today inferred from high-precision reactor neutrino disappearance. The Double Chooz (DC) experiment has played a pioneering role in this channel by providing the first positive evidence, in 2011, in combination with the T2K experiment appearance data. The establishment of $mathbf{theta_{13}}$ awaited the Daya Bay experiments observation in 2012; confirmed soon after by the RENO experiment. Todays best knowledge on $mathbf{theta_{13}}$ from reactor experiments is a key input to many neutrino experiments. Here DC reports its first multi-detector $mathbf{theta_{13}}$ measurement exploiting several unprecedented techniques for a major precision improvement.
The Double Chooz collaboration presents a measurement of the neutrino mixing angle $theta_{13}$ using reactor $overline{ u}_{e}$ 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 1050m 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 $overline{ u}_{e}$ without gadolinium loading. Spectral distortions from the $overline{ u}_{e}$ reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of $sin^{2}2theta_{13} = 0.095^{+0.038}_{-0.039}$(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 $sin^{2}2theta_{13} = 0.088pm0.033$(stat+syst).
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 $sin^2(2theta_{13})=$ 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.
A non zero, surprisingly large value of the third mixing angle $theta_{13}$ has been measured in reactor neutrino experiments. Currently the most precise measurement of $sin^2 2theta_{13}$ has been performed by the Daya Bay experiment $sin^22theta_{13}=0.089pm 0.010({rm stat.})pm0.005({rm syst.})$ (7.7 $sigma$ significance of $sin^22theta_{13} > 0$),the RENO experiment has measured the value $sin^2 2theta_{13} = 0.113 pm 0.013(rm stat.) pm 0.019(rm syst.)$ (4.9 $sigma$ significance) and the Double Chooz experiment $sin^2 2theta_{13} = 0.109 pm 0.030(rm stat.) pm 0.025(rm syst.)$ (2.9 $sigma$ significance). These results are extremely important for future searches of violation of combined CP parity in lepton sector of the Standard model.
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