STEREO search for a sterile neutrino at the ILL Grenoble reactor

International audienceIn the recent years, many acomplishments for neutrino physics were made close to nuclear reac-tors. The smallest mixing angle, θ 13 was determined with high precision and the emitted antineu-trino spectra was measured with unprecedent resolution. However, two anomalies concerning theabsolute flux (smaller than the prediction) and the spectral shape (presence of a "bump" at ener-gies around 5 MeV) have yet to be solved. While they seem together to point towards a wrongprediction in the antineutrino spectra due to underestimated systematics in the measurementsofthe beta spectra emitted after fission or in the conversion method, the first anomaly, known asthe Reactor Antineutrino Anomaly, could also be solved by introducting a fourth neutrino masseigenstate of the eV mass participating in the oscillation phenomenon. To finally solve this puz-zle, the Stereo detector has been taking data since the end of 2016 at the Institut Laue Langevinresearch reactor, Grenoble, France. In this contribution, descriptions of the Stereo experimentas well as the pulse shape discrimination parameter based analysis method are given. Then, theresults from 66 days of reactor turned on and 138 days of reactor turned off are reported. Theresulting antineutrino rate is (396.3 ± 4.7) $\overline{ν}$$_{e}$/day and the signal to background ratio about 0.9.The test of a new oscillation toward a sterile neutrino is found to be compatible with the nulloscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5%C.L