Majorana Neutrinos in Same-Sign $W^\pm W^\pm$ Scattering at the LHC: Breaking the TeV Barrier

TL;DR

This paper investigates the potential of the 13 TeV LHC to detect heavy Majorana neutrinos through same-sign W boson scattering, extending the mass reach beyond current searches with a detailed simulation and analysis.

Contribution

It introduces a novel collider analysis method for probing heavy Majorana neutrinos in W boson scattering, achieving sensitivity to higher mass ranges than existing approaches.

Findings

Sensitivity to heavy neutrino mixing down to 0.06-0.3 for 1-10 TeV masses at 300 fb^{-1}

Extended mass reach up to 20 TeV for heavy neutrinos with significant mixing

W boson scattering channel enhances detection prospects above a few hundred GeV

Abstract

We revisit the sensitivity to non-resonant, heavy Majorana neutrinos $N$ in same-sign $W^\pm W^\pm$ scattering at the $\sqrt{s}=13$ TeV LHC and its high-luminosity upgrade. As a benchmark scenario, we work in the context of the Phenomenological Type I Seesaw model, relying on a simulation up to next-to-leading order in QCD with parton shower matching. After extensively studying the phenomenology of the $pp\to\mu^\pm\mu^\pm j j$ process at the amplitude and differential levels, we design a simple collider analysis with remarkable signal-background separation power. At 95\% confidence level we find that the squared muon-heavy neutrino mixing element $\vert V_{\mu N} \vert^{2}$ can be probed down to about $0.06-0.3 ~ (0.03-0.1)$ for $m_N = 1-10~{\rm TeV}$ with $\mathcal{L}=300$ fb$^{-1}~(3$ ab$^{-1})$. For heavier masses of $m_N = 20~{\rm TeV}$, we report sensitivity for $\vert V_{\mu N} \vert^{2}\gtrsim 0.5~(0.3)$. The $W^\pm W^\pm$ scattering channel can greatly extend the mass range covered by current LHC searches for heavy Majorana neutrinos and particularly adds invaluable sensitivity above a few hundred GeV. We comment on areas where the analysis can be improved as well as on the applicability to other tests of neutrino mass models.