Search for t' pair production in lepton+jets channel

A search is presented for the pair production of a fourth-generation $t'$ quark and its antiparticle in proton-proton collisions at $\sqrt{s} = 7$~TeV provided by the Large Hadron Collider. The data were collected by the CMS detector during the 2011 collider run. The $t'$ quark is assumed to decay exclusively to a $W$ boson and a $b$ quark. The search is carried out using events with a single isolated electron or muon, large missing transverse momentum, and at least four jets with large transverse momenta, one of which must be identified as originating from the fragmentation of a $b$ quark. The data analyzed correspond to an integrated luminosity of 573 pb$^{-1}$ for the electron channel and 821 pb$^{-1}$ for the muon channel. No significant excess over standard model expectations is observed. Assuming strong pair production of $t'$ quarks, a lower limit is set on the $t'$ quark mass of 450~GeV at 95\% confidence level.