Production of extra quarks decaying to Dark Matter beyond the Narrow Width Approximation at the LHC

This paper explores the effects of finite width in processes of pair production of an extra heavy quark with charge 2/3 (top partner) and its subsequent decay into a bosonic Dark Matter (DM) candidate – either scalar or vector – and SM up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the extra quarks have a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.