Observation of Reactor Antineutrinos with the CHANDLER Detector

Experimental anomalies hint at the possible existence of a sterile neutrino. Several experiments have been searching for the sterile neutrino, but none can claim either its discovery or fully rule it out. To test the sterile neutrino hypothesis, we search for short baseline oscillations using antineutrinos from nuclear reactors. We have developed a reactor antineutrino detection technology based on solid plastic scintillator, called CHANDLER, which could be used to search for short baseline reactor antineutrino oscillations. An 80 kg prototype was deployed at a commercial nuclear reactor for four and a half months with minimal shielding and no overburden. We detected an antineutrino signal of 2880 inverse beta decay events, with 5.5σ significance. This measurement represents the first observation of reactor antineutrinos in a surface-deployed, mobile neutrino detector. We envisioned several improvements to the detector from this deployment, which will be tested in an upgrade of this prototype. The full-scale detector will be able to search for sterile neutrinos and could also be used for nuclear non-proliferation applications.