Search for Electron Neutrino Appearance at the $\Delta m^2\sim 1{\mathrm{eV}}^2$ Scale

The MiniBooNE Collaboration reports first results of a search for ${\nu }_e$ appearance in a ${\nu }_{\mu }$ beam. With two largely independent analyses, we observe no significant excess of events above the background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model.

Figure 1

Events in MiniBooNE are reconstructed as either a muon event, an electron event, or a ${\pi }^0$ event.

Figure 2

The top plot shows the number of candidate ${\nu }_e$ events as a function of $E_{\nu }^{\mathrm{QE}}$. The points represent the data with statistical error, while the histogram is the expected background with systematic errors from all sources. The vertical dashed line indicates the threshold used in the two-neutrino oscillation analysis. Also shown are the best-fit oscillation spectrum (dashed histogram) and the background contributions from ${\nu }_{\mu }$ and ${\nu }_e$ events. The bottom plot shows the number of events with the predicted background subtracted as a function of $E_{\nu }^{\mathrm{QE}}$, where the points represent the data with total errors and the two histograms correspond to LSND solutions at high and low $\Delta m^2$.

Figure 3

The top plot shows the MiniBooNE 90% C.L. limit (thick solid curve) and sensitivity (dashed curve) for events with $475<E_{\nu }^{\mathrm{QE}}<3000\mathrm{MeV}$ within a two-neutrino oscillation model. Also shown is the limit from the boosted decision tree analysis (thin solid curve) for events with $300<E_{\nu }^{\mathrm{QE}}<3000\mathrm{MeV}$. The bottom plot shows the limits from the KARMEN [2] and Bugey [32] experiments. The MiniBooNE and Bugey curves are 1-sided upper limits on ${sin}^{2}2\theta$ corresponding to $\Delta {\chi }^2=1.64$, while the KARMEN curve is a “unified approach” 2D contour. The shaded areas show the 90% and 99% C.L. allowed regions from the LSND experiment.