  The STEREO experiment is a very short baseline reactor antineutrino
experiment. It is designed to test the hypothesis of light sterile neutrinos
being the cause of a deficit of the observed antineutrino interaction rate at
short baselines with respect to the predicted rate, known as the reactor
antineutrino anomaly. The STEREO experiment measures the antineutrino energy
spectrum in six identical detector cells covering baselines between 9 and 11 m
from the compact core of the ILL research reactor. In this article, results
from 179 days of reactor turned on and 235 days of reactor turned off are
reported at a high degree of detail. The current results include improvements
in the modelling of detector optical properties and the gamma-cascade after
neutron captures by gadolinium, the treatment of backgrounds, and the
statistical method of the oscillation analysis. Using a direct comparison
between antineutrino spectra of all cells, largely independent of any flux
prediction, we find the data compatible with the null oscillation hypothesis.
The best-fit point of the reactor antineutrino anomaly is rejected at more than
99.9% C.L.
