Search for Light Sterile Neutrinos With Two Neutrino Beams at MicroBooNE

TL;DR

This study uses data from the MicroBooNE detector with two neutrino beams to test the sterile neutrino hypothesis and finds no evidence supporting the existence of a light sterile neutrino to explain previous anomalies.

Contribution

First measurement employing two accelerator neutrino beams to break degeneracies in sterile neutrino searches, providing new constraints on sterile neutrino models.

Findings

Excluded the single light sterile neutrino explanation of LSND and MiniBooNE anomalies at 95% CL.

Ruled out a significant part of the parameter space for sterile neutrino-induced oscillations.

Found no evidence for neutrino flavor transitions indicative of sterile neutrinos.

Abstract

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 $\nu_{\mu}\rightarrow\nu_{e}$ 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 $\nu_{\mu}\rightarrow\nu_{e}$ flavour transitions or $\nu_{e}$ disappearance that would indicate non-standard flavour oscillations. Our results show that previous anomalous observations consistent with $\nu_{\mu}\rightarrow\nu_{e}$ transitions cannot be explained by introducing a single sterile neutrino state.