STEREO

STEREO is an experiment studying neutrinos from nuclear reactors at very short distances and with a precision of the order of a percent. Its aim is to understand whether there is a 4th neutrino with a square mass around 1eV2, 10 to 100 times heavier than the well-established neutrinos νe, νμ and ντ. This 4th state, called the “sterile neutrino”, would interact even more rarely than the known neutrinos and would explain the observed deficit of neutrinos from reactors compared with predictions (called the “Reactor Anomaly”).

An oscillation of neutrinos in this 4th state results in the disappearance of these particles. STEREO, installed 10 m from the core of the research reactor at the Institut Laue-Langevin (ILL) in Grenoble, took data between 2016 and 2020. Their analysis, published in 2023 by the journal Nature, represents a major advance in our understanding of the Reactor Anomaly. It has also provided valuable data on reactor neutrinos for future experiments in this field.