The Stereo Experiment: the Search for eV Sterile Neutrinos

Nuclear reactors are an intense and pure source of low energy electron antineutrinos. In combination with other sources, they have been used to discover and understand neutrino oscillations. However, two unsolved anomalies have appeared during the study of the reactor neutrinos: one related to the neutrino spectral shape, and another to the absolute neutrino flux. The latter, known as the Reactor Antineutrino Anomaly, presents a deficit in the observed flux compared to the expected at very short baselines (distance $<$ 100 meters). This anomaly could point to the existence of a light sterile neutrino participating in the oscillation phenomena, and a way to prove it is the study of the reactor neutrino flux at very short baselines. The Stereo experiment, taking data since November 2016, is trying to resolve this anomaly. It is placed at 10 meters from the compact, highly enriched ${}^{235}$U fuel element of the research reactor of the Institut Laue Langevin (Grenoble, France). The detector target is segmented in six cells providing a multiple baselines analysis. Oscillations to a sterile neutrino in the eV mass scale can be identified by characteristic distortions in the neutrino energy spectrum of the different cells. The most recent results of this experiment are going to be presented in this talk.