Results are presented from a search for heavy bottom-like quarks, produced in pairs in pp collisions at √s = 7 TeV, undertaken with the CMS experiment at the LHC. The b′ quarks are assumed to decay exclusively to a top quark and a W boson (tW). The b′ anti-b′ to t W⁺ anti-t 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 (inverse femtobarns), observed events are compared to the Standard Model background predictions, and the existence of b′ quarks having masses below 611 GeV/c² is excluded at 95% confidence level.