Search for heavy lepton partners of neutrinos in pp collisions at 8 TeV, in the context of type III seesaw mechanism

A direct search for the heavy fermion weak triplet mediators of the type III seesaw mechanism is presented. The analysed data were collected with the CMS detector at the LHC in 2012 at $\sqrt{s}$ = 8 TeV. The integrated luminosity is 19.7 ${\text{fb}}^{-1}$. Seesaw heavy fermions can be produced in LHC proton-proton collisions through quark-annihilation via a virtual boson followed by decays into standard model bosons and leptons. The search is performed using final states with exactly three isolated charged leptons and an imbalance in transverse momentum. No excess of events is observed above the standard model background. The results are interpreted in terms of limits on production cross sections and limits on weak triplet masses. The results are derived for a specific choice as well as for a range of mixing parameters. $$\textit{This document has been revised with respect to the version dated March 10, 2015.}$$