Search for new particles decaying to a jet and an emerging jet

A search for events consistent with the pair production of a heavy mediator particle that decays to a light quark and a new fermion, called a dark quark, is performed using data corresponding to an integrated luminosity of $16.1~\mathrm{fb}^{-1}$ from proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ collected by the CMS experiment at the LHC in 2016. The dark quark is charged only under a new quantum chromodynamic-like force, and forms long-lived dark hadrons via a parton shower. The resulting emerging jet contains displaced vertices that are created by dark hadron decays to standard model hadrons. Mediator particles with masses between 400 and $1250~\mathrm{GeV}$ are excluded for dark hadron decay lengths between 5 and $225~\mathrm{mm}$. This analysis is the first dedicated search for new particles that decay to a jet and this kind of emerging jet. $$\textit{This document has been revised with respect to the version dated June 21, 2018.}$$