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Register a new userDouble Chooz, A Search for the Neutrino Mixing Angle theta-13
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Authors
Maury Goodman Thierry Lasserre
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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.
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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.
Tremendous progress has been achieved in neutrino oscillation physics during the last few years. However, the smallness of the $t13$ neutrino mixing angle still remains enigmatic. The current best constraint comes from the CHOOZ reactor neutrino experiment $s2t13 < 0.2$ (at 90% C.L., for $adm2=2.0 10^{-3} text{eV}^2$). We propose a new experiment on the same site, Double-CHOOZ, to explore the range of $s2t13$ from 0.2 to 0.03, 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 cosmic ray induced background. Therefore, Double-CHOOZ will use two identical detectors, one at $sim$150 m and another at 1.05 km distance from the nuclear cores. The plan is to start data taking with two detectors in 2008, and to reach a sensitivity of 0.05 in 2009, and 0.03 in 2011.
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.
We present a search for signatures of neutrino mixing of electron anti-neutrinos with additional hypothetical sterile neutrino flavors using the Double Chooz experiment. The search is based on data from 5 years of operation of Double Chooz, including 2 years in the two-detector configuration. The analysis is based on a profile likelihood, i.e. comparing the data to the model prediction of disappearance in a data-to-data comparison of the two respective detectors. The analysis is optimized for a model of three active and one sterile neutrino. It is sensitive in the typical mass range $5 cdot 10^{-3} $ eV$^2 lesssim Delta m^2_{41} lesssim 3cdot 10^{-1} $ eV$^2$ for mixing angles down to $sin^2 2theta_{14} gtrsim 0.02$. No significant disappearance additionally to the conventional disappearance related to $theta_{13} $ is observed and correspondingly exclusion bounds on the sterile mixing parameter $theta_{14} $ as function of $ Delta m^2_{41} $ are obtained.
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.
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