Detector energy calibration in the STEREO neutrino experiment

Abstract

The STEREO experiment was developed to investigate the hypothesis of a light sterile neutrino arising from the observed discrepancy between measured reactor antineutrino fluxes and revised flux predictions, known as the Reactor Antineutrino Anomaly. The detector is located at 10 m from the compact nuclear reactor core of the Institut Laue- Langevin. The segmentation of the detector target in 6 cells allows measuring the neutrino energy spectrum at different baselines. Antineutrino interactions are detected by the inverse beta-decay reaction in Gd-loaded liquid scintillator. STEREO started taking data in November 2016. About 70 days of data have been recorded during reactor operation and 25 days during reactor shut down. STEREO plans to record 150 days more in 2018. To perform a correct energy reconstruction of neutrino events, the detector energy response must be determined accurately. Different radioactive gamma-ray sources, from 0,5 to 4,4 MeV, are used to constrain the non-linearity of the scintillator response. Calibration data analysis provides the relation between the charge detected by the photomultipliers and the true deposited gamma energy obtained by simulations. The main goal is to reconstruct the energy scale within a 2% uncertainty.