Search for vector-like top quark partners produced in association with Higgs bosons in the diphoton final state

We present a search for a heavy vector-like quark with charge 2/3 (top partner, T). We search for events where the top partner is produced in pairs and where at least one of them decays into a top quark and a Higgs boson. We focus on the decays of the Higgs boson to photons to allow for full mass reconstruction. We select events with two photons and large hadronic activity, and we search for a resonance in the diphoton mass distribution. The observed data are in agreement with the standard model prediction. We proceed to set observed (expected) 95\% confidence level upper limits on the production cross section of strong $\mathrm{T\bar{T}}$ production, excluding the existence of top quark partners with mass up to 540 (607)\,GeV using 19.7\,fb$^{-1}$ of integrated luminosity.