  A search for ``emerging jets'' produced in proton-proton collisions at a
center-of-mass energy of 13 TeV is performed using data collected by the CMS
experiment corresponding to an integrated luminosity of 138 fb$^{-1}$. This
search examines a hypothetical dark quantum chromodynamics (QCD) sector that
couples to the standard model (SM) through a scalar mediator. The scalar
mediator decays into an SM quark and a dark sector quark. As the dark sector
quark showers and hadronizes, it produces long-lived dark mesons that
subsequently decay into SM particles, resulting in a jet, known as an emerging
jet, with multiple displaced vertices. This search looks for pair production of
the scalar mediator at the LHC, which yields events with two SM jets and two
emerging jets at leading order. The results are interpreted using two dark
sector models with different flavor structures, and exclude mediator masses up
to 1950 (1950) GeV for an unflavored (flavor-aligned) dark QCD model. The
unflavored results surpass a previous search for emerging jets by setting the
most stringent mediator mass exclusion limits to date, while the flavor-aligned
results provide the first direct mediator mass exclusion limits to date.
