A bstract Results are presented from a search for heavy bottom-like quarks, pair-produced in pp collisions at $ \sqrt {s} = 7 $ TeV, undertaken with the CMS experiment at the LHC. The b′ quarks are assumed to decay exclusively to tW. The $ {\text{b}}\prime \overline {\text{b}} \prime \to {\text{t}}{{\text{W}}^{ - }}\overline {\text{t}} {{\text{W}}^{ + }} $ process can be identified by its distinctive signatures of three leptons or two leptons of same charge, and at least one b-quark jet. Using a data sample corresponding to an integrated luminosity of 4.9 fb −1 , observed events are compared to the standard model background predictions, and the existence of b′ quarks having masses below 611 GeV/ c 2 is excluded at 95% confidence level.