Probing heavy triplet leptons of the type-III seesaw mechanism at future muon colliders

TL;DR

This paper explores the potential to detect heavy triplet leptons predicted by the Type III Seesaw mechanism at future muon colliders, analyzing production processes, decay patterns, and the ability to distinguish neutrino mass hierarchies.

Contribution

It provides a detailed analysis of heavy triplet lepton production and decay at future muon colliders, incorporating neutrino oscillation data and electroweak VBF processes.

Findings

Charged triplet leptons can be probed for masses above ~1 TeV.

The $E^+E^- o ZZ\,\ell^+\ell^-$ channel allows full reconstruction of triplet leptons.

Lepton-number-violating signatures can be observed at 30 TeV muon colliders.

Abstract

We study the search potential of heavy triplet leptons in Type III Seesaw mechanism at future high-energy and high-luminosity muon colliders. The impact of up-to-date neutrino oscillation results is taken into account on neutrino parameters and the consequent decay patterns of heavy leptons in Type III Seesaw. The three heavy leptons in the Casas-Ibarra parametrization with diagonal unity matrix are distinguishable in their decay modes. We consider the pair production of charged triplet leptons $E^+ E^-$ through both $\mu^+\mu^-$ annihilation and vector boson fusion (VBF) processes. The leading-order framework of electroweak parton distribution functions are utilized to calculate the VBF cross sections. The charged triplet leptons can be probed for masses above $\sim 1$ TeV. The $E^+E^-\to ZZ\ell^+\ell^-$ channel can be further utilized to fully reconstruct the three triplet leptons and distinguish neutrino mass patterns. The pair production of heavy neutrinos $N$ and the associated production $E^\pm N$ are only induced by VBF processes and lead to lepton-number-violating (LNV) signature. We also study the search potential of LNV processes at future high-energy muon collider with $\sqrt{s}=30$ TeV.