Abstract:
A search is presented for the pair production of vector-like quarks, $\mathrm{T\bar{T}}$, coupled to $\mathrm{b}$-quarks, and $\mathrm{Q\bar{Q}}$ coupled to light quarks, in proton-proton collisions at $\sqrt{s} = 8$ TeV at the Large Hadron Collider, LHC. The data were collected by the CMS experiment during the 2012 LHC run, and correspond to an integrated luminosity of 19.7 fb$^{-1}$. The $\mathrm{T}$-quark is assumed to decay exclusively to a $\mathrm{W}$ boson and a $\mathrm{b}$-quark, and the $\mathrm{Q}$-quark is assumed to decay to $\mathrm{W}$ and $\mathrm{q}$, where $\mathrm{q}$ is a light quark. The search is carried out using events with a single isolated electron or muon, large missing transverse energy and at least four jets with large transverse momenta. No significant excess over standard model expectations is observed. The result of the analysis is an upper limit on production cross section of vector-like quark times branching ratio in the mass range from 500 GeV to 1 TeV. Under the assumption of strong pair production of vector-like quarks and 100$\%$ branching fractions to $\mathrm{bW}$ or $\mathrm{qW}$, lower limits are set on the quark masses at 95$\%$ C.L.: 912 GeV on the $\mathrm{T}$-quark mass and 788 GeV on the $\mathrm{Q}$-quark mass.
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