Search for $t\bar{t}$ resonances in the semileptonic final state using   pp collisions at $\sqrt s$ = 8 TeV recorded with the CMS detector
  Many extensions to the Standard Model predict gauge interactions with enhanced couplings to third generation quarks, especially the extremely heavy top quark\cite{theoretical}. These phenomena can lead to resonances in the production of $t\bar{t}$ pairs. In this note, a model-independent search for the production of heavy resonances decaying into top-antitop quark pairs in the semileptonic final state using pp collisions at $\sqrt s$ = 8 TeV recorded with the CMS detector is presented.   The analysis focuses on the semileptonic decay channels into electrons or muons and covers the range of 0.5-3 TeV in the invariant mass of the $t\bar{t}$ pairs where the events present specific and different topologies. Therefore two dedicated analyses have been performed to achieve the best sensitivity on the whole invariant mass range: the threshold analysis (0.5-2 TeV) which is optimized for $t\bar{t}$ production at the kinematic production threshold, using standard top quark reconstruction techniques, and the boosted analysis (1-3 TeV) optimized for $t\bar{t}$ produced with high Lorentz boosts, using dedicated techniques for boosted top quarks reconstruction.   No evidence of signal has been found. Thus the following limits at 95% C.L. on the production of non-SM particles in specific models are set: topcolor Z$^{\prime}$ bosons with a width of 1.2 (10) % of its mass are excluded for masses below 2.1 TeV (up to 2.7 TeV). In addition, Kaluza-Klein excitations of a gluon with masses below 2.5 TeV in the Randall-Sundrum model are excluded. 
Anne-Laure Pequegnot
hep-ex