Search for Light Sterile Neutrinos With Two Neutrino Beams at MicroBooNE

The existence of three distinct neutrino flavours, ${\nu }_e$, ${\nu }_{\mu }$, and ${\nu }_{\tau }$, is a central tenet of the Standard Model of particle physics. Quantum-mechanical interference can allow a neutrino of one initial flavour to be detected some time later as a different flavour, a process called neutrino oscillation. Several anomalous observations inconsistent with this three-flavour picture have motivated the hypothesis that an additional neutrino state exists which does not interact directly with matter, termed a “sterile” neutrino, ${\nu }_s$. This includes anomalous observations from the LSND and MiniBooNE experiments, consistent with ${\nu }_{\mu }\to {\nu }_e$ transitions at a distance inconsistent with the three-neutrino picture. Here, we use data obtained from the MicroBooNE liquid-argon time projection chamber in two accelerator neutrino beams to exclude the single light sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level (CL). Additionally, we rule out a significant portion of the parameter space that could explain the gallium anomaly. This is the first measurement to use two accelerator neutrino beams to break a degeneracy between ${\nu }_e$ appearance and disappearance that would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for either ${\nu }_{\mu }\to {\nu }_e$ flavour transitions or ${\nu }_e$ disappearance that would indicate non-standard flavour oscillations. Our results show that previous anomalous observations consistent with ${\nu }_{\mu }\to {\nu }_e$ transitions cannot be explained by introducing a single sterile neutrino state.