Search for pair production of heavy vector-like quarks decaying into hadronic final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A search is presented for the pair production of heavy vector-like quarks, $T\bar{T}$ or $B\bar{B}$, 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 $\sqrt{s}=13$ 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 vector-like quarks decay into a Standard Model boson and a third-generation-quark, $T\to Wb,Ht,Zt$ or $B\to Wt,Hb,Zb$, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vector-like $B$-quark mass for a weak-isospin doublet ($B,Y$) is 950 (890) GeV, and the lower limits on the masses for the pure decays $B\to Hb$ and $T\to Ht$, where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively.

arXiv comment51 pages in total, author list starts at page 35, 14 figures, 3 tables, submitted to Physical Review D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2017-14/

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