Sterile Neutrino Constraints from the STEREO Experiment with 66 Days of Reactor-On Data

Abstract

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 in unprecedented detail. The current results include improvements in the description of the optical model of the detector, 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 interaction rates of all cells, 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.

Reevaluating reactor antineutrino anomalies with updated flux predictions

“…We begin with PROSPECT and STEREO, which have produced early results [63][64][65], but not, at present, final analyses. These experiments were designed in the first half of the decade to conclusively probe the RAA as presented in Ref.…”

Novel opaque scintillator for neutrino detection

“…All these components are known for low absorption of near UV light, high radiopurity, suitable safety properties, chemical inertness and moderate costs. The good performance of a LAB and PPO combination was demonstrated and studied in several multi-ton scale neutrino projects [2][3][4][5][6][7]. The paraffin wax is chemically similar to the n-paraffins also used in the LS of different neutrino detectors [2,9].…”

“…Many applications in the field of neutrino physics call for metal loading of the organic scintillator. Some examples are the gadolinium (Gd) loading to detect neutrons after the inverse beta decay of antineutrinos [2][3][4][5], boron (B) loading in active veto systems [18], tellurium (Te)/neodymium (Nd) loading for neutrinoless double beta decay experiments [19] or indium (In) loading for solar neutrino detection [20]. Metal loading in the NoWaSH approach can be similar as for other LS.…”

Machine learning technique to improve anti-neutrino detection efficiency for the ISMRAN experiment

“…Also an excess of events, in energy region ∼5 MeV, observed in the prompt event spectrum of the reactor ν e induced inverse beta decays (IBD), has opened up new avenues for further studies in reactor based ν e [3][4][5]. Various experiments, using moderate scale (few tonnes) detector, are being proposed or taking data at very short baselines to further understand the properties associated with the reactor anti-neutrinos [6][7][8][9]. The Indian Scintillator Matrix for Reactor Anti-Neutrinos (ISMRAN) experiment is one such detector consisting of plastic scintillator (PS) bars in an array forming an active detection volume of 1.0 ton by weight [10].…”