Down type iso-singlet quarks at the HL-LHC and FCC-hh.

We study the discovery potential of down type iso-singlet quarks, $D$, predicted by the $E_6$ GUT model in the ${pp\rightarrow D\bar{D}\rightarrow ZZd\bar{d} \rightarrow \ell^+\ell^-\ell^+\ell^- d\bar{d}}$ channel at the HL-LHC and FCC-hh colliders. The analysis is performed using a high level analysis description language and its runtime interpreter. The study shows that, using solely this channel, HL-LHC can discover $D$ quarks up to a mass of 710 GeV whereas FCC-hh up to 2430 GeV with data collected in their complete run periods.