Proton fixed-target scintillation experiment to search for millicharged dark matter

We propose a low-cost and movable setup to probe minicharged particles using high-intensity proton fixed-target facilities. This proposal, FerMINI, consists of a scintillator-based detector, requiring multicoincident scintillation signatures within a small time window, located downstream of the proton target of a neutrino experiment. During the collisions of a large number of protons on the target, intense minicharged particle beams may be produced via meson photo-decays and Drell-Yan production. We take advantage of the high statistics, shielding, and potential neutrino-detector-related background reduction to search for minicharged particles in two potential sites: the MINOS near detector hall and the proposed DUNE near detector hall, both at Fermilab. We also explore several alternative designs, including modifications to increase signal yield, and combining this detector technology with existing and planned neutrino detectors to better search for minicharged particles. FerMINI can achieve unprecedented sensitivity for minicharged particles in the MeV to few GeV regime with fractional charge $\epsilon=Q_χ/e$ as low as $10^{-4}$.