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

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=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.

Note:

51 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/

Particle Physics Experiments
p p: scattering
p p: colliding beams
quark: postulated particle
quark: hadronic decay
quark: vector particle
W: hadronic decay
Z0: hadronic decay
final state: hadronic
quark: pair production

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