Searching for heavy neutral lepton and lepton number violation through VBS at high-energy muon colliders

TL;DR

This paper explores the potential of high-energy muon colliders to detect heavy neutral leptons and lepton number violation through vector boson scattering, offering a promising avenue for understanding neutrino properties.

Contribution

It introduces a novel method to search for Majorana heavy neutral leptons and lepton number violation signatures via vector boson scattering at muon colliders, surpassing traditional approaches.

Findings

Establishes exclusion limits on HNL mixing parameters.

Demonstrates sensitivity to the Weinberg operator.

Identifies clean LNV signatures at muon colliders.

Abstract

High-energy muon collider can play as an emitter of electroweak gauge bosons and thus leads to substantial vector boson scattering (VBS) processes. In this work, we investigate the production of heavy neutral lepton (HNL) $N$ and lepton number violation (LNV) signature through VBS at high-energy muon colliders. VBS induces LNV processes $W^\pm Z/\gamma\to \ell^\pm N \to \ell^\pm \ell^\pm W^\mp\to \ell^\pm \ell^\pm q\bar{q}'$ with an on-shell HNL $N$ at $\mu^+\mu^-$ colliders. In analogy to neutrinoless double-beta decay with the HNL in t-channel, the LNV signature $W^+W^+\to \ell^+\ell^+$ can also happen via VBS at same-sign muon collider. They provide clean and robust LNV signatures to tell the nature of Majorana HNLs and thus have more advantageous benefits than direct $\mu\mu$ annihilation. We analyze the potential of searching for Majorana HNL and obtain the exclusion limits on mixing $V_{\ell N}$. Based on this same-sign lepton signature, we also obtain the sensitivity of muon collider to the Weinberg operator.