# Constraints on Mediator Coupled to Heavy Quarks from LHC Data

## TL;DR

This paper uses LHC data to set constraints on a simplified model with a new spin-1 mediator coupled to heavy quarks and dark matter, providing stronger bounds than theoretical limits, especially for mediator masses below 1 TeV.

## Contribution

It applies existing LHC searches to a specific mediator model, deriving new bounds on its couplings and decay modes, especially in scenarios with suppressed couplings to valence quarks.

## Key findings

- LHC constraints surpass unitarity bounds for axial vector couplings.
- Di-jet + missing E_T searches provide the strongest bounds for mediator masses below 1 TeV.
- Searches with double b tags are effective even when the mediator decays invisibly.

## 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 $\chi$. We recast ATLAS and CMS searches for final states containing one or more jet(s) + missing $E_T$, 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 $m_R/m_t$. 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 + missing $E_T$ search with or without double $b$ tag. These bounds are quite strong for $m_R < 1$ 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 $R \rightarrow \chi \bar \chi$ decays are allowed; these are the only sensitive LHC searches if the invisible branching ratio of $R$ is very small or zero.