LHC constraints on a mediator coupled to heavy quarks

Abstract

We apply LHC data to constrain a simplified extension of the Standard Model containing a new spin−1 mediator R, which does not couple to first generation quarks, and a spinor dark matter particle χ. We recast ATLAS and CMS searches for final states containing one or more jet(s) + E̸T, with or without b tags, as well as searches for di–jet resonances with b or t tagging. We find that LHC constraints on the axial vector couplings of the mediator are always stronger than the unitarity bound, which scales like mR/mt. If R has a sizable invisible branching ratio, the strongest LHC bound on both vector couplings and axial vector coupling comes from a di–jet + E̸T search with or without double b tag. These bounds are quite strong for mR<1 TeV, even though we have switched off all couplings to valence quarks. Searches for a di–jet resonance with double b tag lead to comparable bounds with the previous results even if R→χχ¯ decays are allowed; these are the only sensitive LHC searches if the invisible branching ratio of R is very small or zero.