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Neutrino Reactors

In the recent years, experiments based on liquid scintillation detection technique allowed to complete the measurement of the last mixing angle θ13 of the neutrino oscillation matrix, thanks to Daya Bay, Reno and Double Chooz experiments measuring antineteutrino flux from reactor. The low energy threshold of these experiments and the good light yield can benefits to other measurements like solar flux, geoneutrinos,

Measuring the last mixing angle of the PMNS matrix θ13
Liquid Scintillator experiments

Liquid scintillator detectors
Experiment Power GWTh Detector Baseline km Overburden Target Status
Double Chooz 17.3 Far 1050 8.3 Running
Near 410 8.3 Running
Daya Bay 17.3 Far 1650 8.3 Running
Near 470 8.3 Running
Near 570 8.3 Running
Reno 16.4 Far 1440 16.5 Running
Near 410 16.5 Running


Measuring Mass Hierarchy Determination

The reactor experiments take benefit from the large amount of antineutrinos flux emitted by the nuclear reactor cores of power plants. The mass hierarchy will be determined thanks to the precision measurements of their survival probability which can be expanded into the following equation:

P_{ \overset{-}{\nu_e} \rightarrow \overset{-}{\nu_e}}  & =  & 1  - sin^2 \theta_{13}.(cos^2 \theta_{12}.sin^2 \Delta_{13}+sin^2 \theta_{12}.sin^2 \Delta_{32}) - cos^4 \theta_{13}.sin^2 \theta_{12}.sin^2 \Delta_{21} \\
& = & 1 - 2 s^2_{13}c^2_{13} - 4c^2_{13}s^2_{12}c^2_{12}sin^2 \Delta_{21}+2s^2_{13}c^2_{13} 
\sqrt{1-4s^2_{12}c^2_{12}sin^2 \Delta_{21} }.cos(2\Delta_{32} \pm \phi)

where \Delta_{ij}=\frac{\Delta m^2_{ij}}{4E} and tan \, \phi=\frac{c^2_{21}.sin^2 \Delta_{21}}{c^2_{21}.cos^2 \Delta_{21}+s^2_{21}}.

In this expression, a phase \phi appears in the probability. The sign is related to the mass hierarchy configurations and results in a shift on the oscillation as shown in Figure 2. The determination of the mass hierarchy will be done by measuring the oscillation pattern. However, the smallness of the shift will impose important constraints on the energy resolution of the detector which has been estimated at 3\% for 1 MeV and under the reasonnable assumption that uncertainty on the oscillation parameters, especially on \Delta m^2_{23}, will be improved by the current running experiments \citeQian:2012xh. In this context, liquid scintillator based detectors appear to be good candidates to perform this measurement with a very good energy resolution. Nevertheless, the energy response requires to be well calibrated to understand non linearity effects (due to quenching effect, Cherenkov light, electronics...) and keep them under control at the subpercent level.

Among the simulated baselines, the most favorable baseline is defined as 60 km long defining the so called medium baseline. The sensitivity on the mass hierarchy determination requires large statistics with reduced systematic errors. A large research program based on liquid scintillator detectors at a kilo ton scale is under development \citeTakaesu:2013wca.

One of the next challenge in neutrino physics investigate the neutrino mass hierarchy. In a near futur JUNO and RENO-50, based on such technique, have been proposed and they will bring a significant answer to these question.

Futur liquid scintillator detector
Experiment Power GW Th Distance km Target $\Theta_13$ Status
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