Assuming that dark matter particles interact with quarks via a GeV-scale mediator, we study dark matter production in fixed target collisions. The ensuing signal in a neutrino near detector consists of neutral-current events with an energy distributi
on peaked at higher values than the neutrino background. We find that for a $Z$ boson of mass around a few GeV that decays to dark matter particles, the dark matter beam produced by the Main Injector at Fermilab allows the exploration of a range of values for the gauge coupling that currently satisfy all experimental constraints. The NO$ u$A detector is well positioned for probing the presence of a dark matter beam, while future LBNF near-detectors would provide more sensitive probes.
We explore quark interactions mediated by new gauge bosons of masses in the 0.3 - 50 GeV range. A tight upper limit on the gauge coupling of light Z bosons is imposed by the anomaly cancellation conditions in conjunction with collider bounds on new c
harged fermions. Limits from quarkonium decays are model dependent, while electroweak constraints are mild. We derive the limits for a Z boson coupled to baryon number, and then construct a Z model with relaxed constraints, allowing quark couplings as large as 0.2 for a mass of a few GeV.
