Chasing the light sterile neutrino with the STEREO detector

The standard three-family neutrino oscillation model is challenged by a number of observations, such as the reactor antineutrino anomaly (RAA), that can be explained by the existence of sterile neutrinos at the eV mass scale. The STEREO experiment detects ve produced in the 58.3MWTh compact core of the ILL research reactor via inverse beta decay (IBD) interactions in a liquid scintillator. Using 6 identical target cells, STEREO compares ve energy spectra at different baselines in order to observe possible distortions due to short-baseline oscillations toward eV sterile neutrinos. IBD events are effectively singled out from γ radiation by selecting events with a two-fold coincidence that is typical of an IBD interaction. External background is reduced by means of layers of shielding material. A Cherenkov veto allows to partially remove background produced by cosmic muons, and the remaining component is measured in reactor-off periods and subtracted statistically. If no evidence of sterile neutrinos after the full statistics of 6 reactor cycles is gathered, STEREO is expected to fully exclude the RAA allowed region.