A search for bottom-type, vector-like quark pair production in a fully hadronic mode 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), each decaying into a b quark and either a Higgs or a Z boson. The analysis is based on data from proton-proton collisions at a 13 TeV center-of-mass energy recorded by the CMS experiment, corresponding to a total integrated luminosity of $137~\mathrm{fb}^{-1}$. Since the predominant decay modes of the Higgs and Z bosons are to a pair of quarks, the analysis focuses on final states consisting of jets resulting from the six quarks produced in the events. Because the two jets produced in the decay of a highly boosted Higgs or Z boson might merge to form a single jet, three independent analyses are performed, categorized by the number of observed jets. No signal in excess of the expected background is observed. Lower limits are set on the VLQ mass at the $95\%$ confidence level, at 1570 GeV in the case where the VLQ decays exclusively to a b quark and a Higgs boson, 1390 GeV for when it decays exclusively to a b quark and a Z boson, and 1450 GeV for when it decays equally in these two modes.