Search for Light Sterile Neutrinos With Two Neutrino Beams at MicroBooNE

Abstract

The existence of three distinct neutrino flavours, $\hat{I}{½}_e$, $\hat{I}{½}_{\hat{I}}¼$, and $\hat{I}{½}_{\ddot{I}}„$, 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, $\hat{I}{½}_s$. This includes anomalous observations from the LSND and MiniBooNE experiments, consistent with $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_e$ 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 $\hat{I}{½}_e$ appearance and disappearance that would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for either $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_e$ flavour transitions or $\hat{I}{½}_e$ disappearance that would indicate non-standard flavour oscillations. Our results show that previous anomalous observations consistent with $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_e$ transitions cannot be explained by introducing a single sterile neutrino state.

17 pages, 6 figures