Searching Doubly Charged Leptons at Present and Future Colliders

Abstract

The production at the LHC of exotic excited leptons of charge $Q = +2e$ is considered. Such states are predicted in composite models with extended isospin multiplets ($I_{W}=1$ and $I_{W}=3/2$). The coupling among these doubly charged leptons and Standard Model fermions may occurs either via gauge or contact interactions. In the former case the decay channels are more constrained. We study the production cross section at the LHC of $L^{++}$ ($pp \rightarrow L^{++} \, \ell^{-}$) and focus on the leptonic signature deriving from the subsequent decays $L^{++} \rightarrow W^{+} \ell^{+} \rightarrow \ell^{+} \ \ell^{+} \, \nu_l $. The invariant mass distribution of the like-sign dilepton exhibits a sharp end-point corresponding to excited doubly charged lepton mass $m^{*}$. A preliminary study for the production of doubly charged leptons at the future linear colliders, by considering the process $e^{-} e^{-} \rightarrow L_{e}^{--} \, \nu_{e}$, is carried out. Both the contact and gauge interaction mechanisms are investigated and compared.