Search for pair production of heavy vectorlike quarks decaying into hadronic final states in pp collisions at s=13 TeV with the ATLAS detector

Abstract

A search is presented for the pair production of heavy vectorlike quarks, TT ̄ or BB ̄, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying W=Z bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb−1 of proton-proton collisions with a center-of-mass energy of s 1⁄4 13 TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vectorlike quarks decay into a Standard Model boson and a third-generation-quark, T → Wb; Ht; Zt or B → Wt; Hb; Zb, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vectorlike B-quark mass for a weak-isospin doublet (B, Y) is 950 (890) GeV, and the lower limits on the masses for the pure decays B → Hb and T → Ht, where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively.