Topcolor

Abstract: The production cross–section and distributions of the top quark are sensitive to new physics, e.g., the tt system can be a probe of new resonances or gauge bosons that are strongly coupled to the top quark, in analogy to Drell–Yan production. The existence of such new physics is expected in dynamical electroweak symmetry breaking schemes, and associated with the large mass of the top quark. The total top production cross–section can be more than doubled, and distributions significantly distorted with a chosen scale of new physics of ∼ 1 TeV in the vector color singlet or octet s–channel. New resonance physics is most readily discernible in the high–pT distributions of the single top quark and of the W boson.

Abstract: Normalised differential top-quark pair production cross sections are measured in pp collisions at a centre-of-mass energy of 7 TeV at the LHC with the CMS detector using data recorded in 2011 corresponding to an integrated luminosity of 5.0 inverse femtobarns. The measurements are performed in the lepton+jets decay channels (e+jets and mu+jets) and the dilepton decay channels (oppositely charged ee, mu mu, and e mu). The t t-bar differential cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the t t-bar system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed.

Abstract: A search is presented for a massive particle, generically referred to as a Z′, decaying into a tt pair. The search focuses on Z′ resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb^(−1). Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z′ modeled for several widths, as well as for a Randall-Sundrum Kaluza-Klein gluon. In addition, the result contrain any enhancement in tt production beyond expectations of the standard mode for tt invariant mass larger than 1 TeV/c^2.