First Measurement of Monoenergetic Muon Neutrino Charged Current Interactions

We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest ($K^{+}\to {\mu }^{+}{\nu }_{\mu }$) at the NuMI beamline absorber. These signal ${\nu }_{\mu }$-carbon events are distinguished from primarily pion decay in flight ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ backgrounds produced at the target station and decay pipe using their arrival time and reconstructed muon energy. The significance of the signal observation is at the $3.9\sigma$ level. The muon kinetic energy, neutrino-nucleus energy transfer ($\omega =E_{\nu }-E_{\mu }$), and total cross section for these events are extracted. This result is the first known-energy, weak-interaction-only probe of the nucleus to yield a measurement of $\omega$ using neutrinos, a quantity thus far only accessible through electron scattering.

Figure 1

The NuMI beamline and various sources of neutrinos that reach MiniBooNE (dashed lines). The signal KDAR neutrinos (solid line) originate mainly from the absorber.

Figure 2

The normal time data distribution (black points with error bars) with the best-fit signal template (green) stacked on the inferred background (orange). The inset shows the relative event rate for early time, late time, and normal time after normalizing the three distributions in the background-only region (${\mathtt{PMThits}}_{\mathtt{5}\mathtt{ns}}>120$). A deficit (excess) of KDAR-like events at early (late) times can be seen.

Figure 3

(Left) the three early-time, background-enhanced bins. (Right) the three late-time, signal-enhanced bins. The data (black solid line with stat-only error bar), best-fit signal (green), best-fit background (orange), and total $\text{signal}+\text{background}$ (black dotted-line) distributions are shown.

Figure 4

The best fit $T_{\mu }$ (red-dashed) and $\omega$ (blue-dashed) spectra with shape-only $1\sigma$ error bands, given a fixed end point of $T_{\mu }^{\max }=95\mathrm{MeV}$. The distributions are fully correlated.