A search for bottom-type, vector-like quark pair production in leptonic and fully hadronic final states in proton-proton collisions at $\sqrt{s} = 13$ TeV

A search is described for the production of a pair of bottom-type vector-like quarks (VLQs) with a mass greater than 1000 GeV. Each VLQ decays into a b quark and a Higgs boson, a b quark and a Z boson, or a t quark and a W boson. This analysis considers both fully hadronic final states and those containing a lepton pair from a Z boson decay. The products of the hadronic Higgs, Z, or W boson decays can be resolved as two distinct jets or merged into a single jet, so the final states are separated by the number of reconstructed jets. The analysis uses data corresponding to a total integrated luminosity of 138 $\mathrm{fb}^{-1}$ collected in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ by the CMS detector at the LHC from 2016 to 2018. No signal in excess of the expected background is observed, and lower limits are set on the VLQ mass at $95\%$ confidence level. These depend on the VLQ branching fractions and are 1570 GeV and 1540 GeV for $100\%$ B $\rightarrow$ bH and $100\%$ B $\rightarrow$ bZ, respectively. For many cases, they exceed by 100 GeV or more those of previous results.