First search for dark-trident processes using the MicroBooNE detector

Abstract

We present a first search for dark-trident scattering in a neutrino beam using a data set corresponding to $7.2\times 10^{20}$ protons on target taken with the MicroBooNE detector at Fermilab. Proton interactions in the neutrino target at the Main Injector produce $\ddot{I}{€}^0$ and $\hat{I}\cdot$ mesons, which could decay into dark-matter (DM) particles mediated via a dark photon $A^{\prime }$. A convolutional neural network is trained to identify interactions of the DM particles in the liquid-argon time projection chamber (LArTPC) exploiting its image-like reconstruction capability. In the absence of a DM signal, we provide limits at the $90\%$ confidence level on the squared kinematic mixing parameter ${\epsilon }^2$ as a function of the dark-photon mass in the range $10\le M_{A^{\prime }}\le 400$ MeV. The limits cover previously unconstrained parameter space for the production of fermion or scalar DM particles $\ddot{I}‡$ for two benchmark models with mass ratios $M_{\ddot{I}}‡/M_{A^{\prime }}=0.6$ and $2$ and for dark fine-structure constants $0.1\le \hat{I}{\pm }_D\le 1$.