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 dataset corresponding to 7.2×1020 protons on target taken with the MicroBooNE detector at Fermilab. Proton interactions in the neutrino target at the main injector produce 𝜋��0 and 𝜂�� mesons, which could decay into dark-matter (DM) particles mediated via a dark photon 𝐴��′. A convolutional neural network is trained to identify interactions of the DM particles in the liquid-argon time projection chamber (LArTPC) exploiting its imagelike reconstruction capability. In the absence of a DM signal, we provide limits at the 90% confidence level on the squared kinematic mixing parameter 𝜖��2 as a function of the dark-photon mass in the range 10≤𝑀��𝐴��′≤400 MeV. The limits cover previously unconstrained parameter space for the production of fermion or scalar DM particles 𝜒�� for two benchmark models with mass ratios 𝑀��𝜒��/𝑀��𝐴��′=0.6 and 2 and for dark fine-structure constants 0.1≤𝛼��𝐷��≤1.