Search for pair production of heavy vector-like quarks decaying to high-$p_{mathrm{T}}$ $W$ bosons and $b$ quarks in the lepton-plus-jets final state in $pp$ collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

摘要

A search is presented for the pair production of heavy vector-like $T$ and$B$ quarks, primarily targeting the $T$ quark decays to a $W$ boson and a$b$-quark. The search is based on $36.1$ fb$^{-1}$ of $pp$ collisions at$\sqrt{s}$ = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at theCERN Large Hadron Collider. Data are analysed in the lepton-plus-jets finalstate, including at least one $b$-tagged jet and a large-radius jet identifiedas originating from the hadronic decay of a high-momentum $W$ boson. Nosignificant deviation from the Standard Model expectation is observed in thereconstructed $T$ mass distribution. The observed 95\% confidence level lowerlimit on the $T$ mass are 1350 GeV assuming 100\% branching ratio to $Wb$. Inthe SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search isalso sensitive to a heavy vector-like $B$ quark decaying to $Wt$ and otherfinal states. The results are thus reinterpreted to provide a 95\% confidencelevel lower limit on the $B$ quark mass at 1250 GeV assuming 100\% branchingratio to $Wt$; in the SU(2) singlet scenario, the limit is 1080 GeV. Masslimits on both $T$ and $B$ production are also set as a function of the decaybranching ratios. The 100\% branching ratio limits are found to be applicableto heavy vector-like $Y$ and $X$ production that decay to $Wb$ and $Wt$,respectively.