# Results from the STEREO Experiment with 119 days of Reactor-on Data

## TL;DR

The STEREO experiment analyzed 119 days of reactor-on data to test for sterile neutrino oscillations, finding results compatible with no oscillation and excluding the Reactor Antineutrino Anomaly at 99% confidence level.

## Contribution

This study provides new experimental data and analysis methods for short baseline neutrino oscillation tests, specifically addressing the Reactor Antineutrino Anomaly.

## Key findings

- No evidence for sterile neutrino oscillation was observed.
- The Reactor Antineutrino Anomaly is excluded at 99% confidence level.
- The measured antineutrino rate was (365.7 ± 3.2) per day.

## Abstract

In the past decades, short baseline neutrino oscillation studies around experimental or commercial reactor cores have revealed two anomalies. The first one is linked to the absolute flux and the second one to the spectral shape. The first anomaly, called Reactor Antineutrino Anomaly (RAA), could be explained by the introduction of a new oscillation of antineutrinos towards a sterile state of the eV mass. The \stereo detector has been taking data since the end of 2016 at 10~m from the core of the Institut Laue-Langevin research reactor, Grenoble, France. The separation of its Target volume along the neutrino propagation axis allows for measurements of the neutrino spectrum at multiple baselines, providing a clear test of an oscillation at short baseline. In this contribution, a special focus is put on the data analysis and the neutrino extraction using the Pulse Shape Discrimination observable. The results from 119 days of reactor turned on and 210 days of reactor turned off are then reported. The resulting antineutrino rate is (365.7~$\pm$~3.2) \anue /day. The test of a new oscillation towards a sterile neutrino is found to be compatible with the non-oscillation hypothesis and the best fit of the RAA is excluded at 99\% C.L.