First Measurement of $\eta$ Meson Production in Neutrino Interactions on Argon with MicroBooNE

We present a measurement of $\eta$ production from neutrino interactions on argon with the MicroBooNE detector. The modeling of resonant neutrino interactions on argon is a critical aspect of the neutrino oscillation physics program being carried out by the DUNE and Short Baseline Neutrino programs. $\eta$ production in neutrino interactions provides a powerful new probe of resonant interactions, complementary to pion channels, and is particularly suited to the study of higher-order resonances beyond the $\mathrm{\Delta }(1232)$. We measure a flux-integrated cross section for neutrino-induced $\eta$ production on argon of $3.22\pm 0.84(\mathrm{stat})\pm 0.86(\mathrm{syst})$ ${10}^{-41}{\mathrm{cm}}^2/\text{nucleon}$. By demonstrating the successful reconstruction of the two photons resulting from $\eta$ production, this analysis enables a novel calibration technique for electromagnetic showers in GeV accelerator neutrino experiments.

Figure 1

Event display of candidate $\eta$ event.

Figure 2

Distribution of $M_{\gamma \gamma }$ for selected $\eta$ candidates showing data (data points with statistical uncertainties denoted by the error bar) and the predicted event rate (stacked histogram). Different colors denote different topologies, as described in the legend. The gray error band denotes the systematic uncertainty on the predicted event rate.

Figure 3

Reconstructed invariant mass of the hadronic system utilizing the four-momenta of the reconstructed $\eta$ and leading proton (if identified) in the event. The black solid line and data points show the distribution for $\eta$ candidate events predicted and observed, respectively. The distributions in red show the same reconstructed quantity for events from the MicroBooNE data compared to prediction from the ${\pi }^0$ sideband, normalized to the same number of events from the prediction for the $\eta$ selection.