Search for single production of a vector-like T quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector

A search is made for a vector-like T quark decaying into a Higgs boson and a top quark in 13 TeV protonproton collisions using the ATLAS detector at the Large Hadron Collider with a data sample corresponding to an integrated luminosity of 139 fb−1 . The all-hadronic decay modes H → b ¯b and t → bW → bqq¯ ′ are reconstructed as large-radius jets and identified using tagging algorithms. Improvements in background estimation, signal discrimination, and a larger data sample, contribute to an improvement in sensitivity over previous all-hadronic searches. No significant excess is observed above the background, so limits are set on the production cross-section of a singlet T quark at 95\% confidence level, depending on the mass, mT , and coupling, κT , of the vector-like T quark to Standard Model particles. This search targets a mass range between 1.0 to 2.3 TeV, and a coupling value between 0.1 to 1.6, expanding the phase space of previous searches. In the considered mass range, the upper limit on the allowed coupling values increases with mT from a minimum value of 0.35 for 1.07 < mT < 1.4 TeV up to 1.6 for mT = 2.3 TeV.