Search for a vector-like quark T$'$$\to$ tH via the diphoton decay mode of the Higgs boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for the electroweak production of a vector-like quark T
0
, decaying to a
top quark and a Higgs boson is presented. The search is based on a sample of proton-proton
collision events recorded at the LHC at √
s = 13 TeV, corresponding to an integrated
luminosity of 138 fb−1
. This is the first T
0
search that exploits the Higgs boson decay to a
pair of photons. For narrow isospin singlet T
0
states with masses up to 1.1 TeV, the excellent
diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to
previous searches based on the same production mechanism. The electroweak production
of a T
0
quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a
coupling strength κT = 0.25 and a relative decay width Γ/MT
0 < 5%.