Heavy lepton pair production at LHC: model discrimination with multi-lepton signals

TL;DR

This paper investigates how multi-lepton signals at the LHC can be used to distinguish between different models of heavy leptons, focusing on their production, decay signatures, and the Majorana or Dirac nature of neutrinos.

Contribution

It introduces a comprehensive analysis of multi-lepton final states to differentiate heavy lepton models and determine neutrino nature at the LHC.

Findings

Trilepton final state is highly sensitive for heavy neutrino searches.

Like-sign dilepton signals indicate Majorana neutrinos.

Large missing energy signals suggest Dirac triplet models.

Abstract

If new leptons exist close to the electroweak scale, they can be produced in pairs at LHC through standard or new interactions. We study the production of heavy lepton pairs in SM extensions with: (i) a Majorana or Dirac lepton triplet, as those appearing in type-III seesaw; (ii) a lepton isodoublet (N,E)_{L,R}; (iii) a charged isosinglet E_{L,R}; (iv) a Majorana or Dirac neutrino singlet N and an additional Z' gauge boson. It is shown that the trilepton final state l+-l+-l-+, which has a small SM background, constitutes the golden channel for heavy neutrino searches, being very sensitive to Majorana or Dirac neutrinos in triplet, doublet or singlet SU(2)_L representations. For higher luminosities, signals in this final state can also distinguish lepton triplets from doublets and singlets. The Majorana or Dirac nature of the heavy neutrinos is revealed by the presence or not of like-sign dilepton l+-l+- signals without significant missing energy. Notably, l+-l+- signals but with large missing energy are characteristic of Dirac triplets, distinguishing them from the other two models with a heavy Dirac neutrino. Further discrimination is achieved with the analysis of the clean l+l+l-l- final state.