# 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

## TL;DR

This paper reports a search for a vector-like T' quark decaying to a top quark and a Higgs boson, using the Higgs decay to diphotons at 13 TeV proton-proton collisions, setting new exclusion limits up to 960 GeV.

## Contribution

First search exploiting Higgs to diphoton decay for T' quark detection, enhancing sensitivity with high diphoton mass resolution at the LHC.

## Key findings

- Excluded T' masses up to 960 GeV at 95% CL
- Achieved diphoton mass resolution of 1-2%
- Set constraints on T' production assuming specific coupling and width

## Abstract

A search for the electroweak production of a vector-like quark T$'$, 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 $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. This is the first T$'$ search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet T$'$ 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$'$ quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength $\kappa_\mathrm{T}$ = 0.25 and a relative decay width $\Gamma/M_{\mathrm{T}'}$ $\lt$ 5%.