Search for pair-produced vector-like quarks of charge -1/3 in lepton+jets final state in pp collisions at sqrt(s) = 8 TeV

Results are presented from an inclusive search for the pair production of vector-like bottom quark partners $\rm{b'}$ that decay into tW, bZ or bH final states. The search is performed using a sample of proton-proton collisions at $\sqrt{s} = 8$ TeV collected with the CMS detector and corresponding to an integrated luminosity up to 19.8 fb$^{-1}$ . The signal region is defined by events containing one electron or muon, missing transverse momentum, and at least four jets with large transverse momenta, where one jet is likely to originate from the decay of a bottom quark. Events are further categorized based on the number of jets that are consistent with the decay of boosted W, Z or H bosons. No significant excess of events is observed with respect to the standard model expectations. Assuming a strong pair-production mechanism, 95 percent confidence level limits between 582 and 732 GeV are set on the $\rm{b'}$ quark mass for various decay branching ratios. If the $\rm{b'}$ decays exclusively into a top quark and a W boson, $\rm{b'}$ quark masses below 732 GeV are excluded at the 95 percent confidence level.