PoS - Proceedings of Science
Volume 340 - The 39th International Conference on High Energy Physics (ICHEP2018) - Parallel: Neutrino Physics
STEREO search for a sterile neutrino at the ILL Grenoble reactor
L. Bernard
Full text: pdf
Published on: August 02, 2019
In 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 the
absolute 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 wrong
prediction in the antineutrino spectra due to underestimated systematics in the measurementsof
the beta spectra emitted after fission or in the conversion method, the first anomaly, known as
the Reactor Antineutrino Anomaly, could also be solved by introducting a fourth neutrino mass
eigenstate 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 Langevin
research reactor, Grenoble, France. In this contribution, descriptions of the Stereo experiment
as well as the pulse shape discrimination parameter based analysis method are given. Then, the
results from 66 days of reactor turned on and 138 days of reactor turned off are reported. The
resulting 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 null
oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5%
DOI: https://doi.org/10.22323/1.340.0064
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