Search for dark matter in final states with a leptoquark and missing transverse momentum in proton-proton collisions at 13 TeV

A search for dark matter is presented in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13~\mathrm{TeV}$ using events with at least one high transverse momentum ($p_{\mathrm{T}}$) muon, at least one high $p_{\mathrm{T}}$ jet, and large missing transverse momentum. The search is performed in the context of the so-called coannihilation codex, a new paradigm that introduces novel scenarios for dark matter production. The data were collected with the CMS detector at the CERN LHC in 2016 and 2017, and correspond to an integrated luminosity of $77.4~\mathrm{fb}^{-1}$. In the examined scenario, a pair of scalar leptoquarks is assumed to be produced. One leptoquark decays to a muon and a jet while the other decays to dark matter and soft standard model particles. The dark matter signature is given by a peak at the leptoquark mass in the invariant mass distribution of the highest $p_{\mathrm{T}}$ muon and jet. The data are observed to agree with the predictions from the standard model. Leptoquarks with masses up to $1160~\mathrm{GeV}$ are excluded.