  Since many of the dark-sector particles interact with Standard Model (SM)
particles in multiple ways, they can appear in experimental facilities where SM
particles appear in abundance. In this study, we explore a particular class of
longer-lived mediators that are produced from photons, charged mesons, neutral
mesons, and $e^\pm$ that arise in proton-beam fixed-target-type neutrino
experiments. This class of mediators encompasses light scalars that appear in
theories like extended Higgs sectors, muon(electro)philic scalars, etc. We
evaluate the sensitivities of these mediators at beam-based neutrino
experiments such as the finished ArgoNeuT, ongoing MicroBooNE, SBND, ICARUS,
and the upcoming DUNE experiment. We realize that scalars are more enhanced
while produced from three-body decay of charged mesons, especially if they are
muonphilic in nature. For scenarios that contain muonphilic scalars, these
experiments can probe unexplored regions of parameter space that can explain
the current discrepancy in the anomalous magnetic moment of muons. The
sensitivity of electrophilic scalars at the DUNE Near Detector can explore new
regions. We also show that Bethe-Heitler scattering processes can be used to
probe flavor-specific lepton final states even for the mediator masses below
twice the lepton mass.
