Revealing the Origin of Neutrino Masses through Displaced Shower Searches in the CMS Muon System

TL;DR

This paper explores how displaced shower searches in the CMS muon system can reveal the origin of neutrino masses by detecting long-lived right-handed neutrinos, achieving sensitivity near the seesaw mechanism's minimal mixing.

Contribution

It demonstrates the potential of CMS displaced shower searches to probe neutrino mass models, especially at and below the seesaw floor, using existing and future collider data.

Findings

CMS search is sensitive to $|V_{\ell N}|^2 \approx 10^{-12}$ for $m_N \approx 40$ GeV

Existing data constrains key neutrino mass generation scenarios

Projected HL-LHC sensitivity motivates dedicated long-lived RHN searches

Abstract

We study the potential to probe the origin of neutrino masses, by searching for long-lived right-handed neutrinos (RHNs) $N$ in the $B-L$ model and in the RHN-extended Standard Model (SM) Effective Field Theory (EFT). Despite the small active-sterile mixing $|V_{\ell N}|^2$, RHNs are produced abundantly via SM and exotic Higgs production, as long as the Higgs mixing or EFT operator coefficient is sufficiently large. We reinterpret a search for displaced showers in the CMS muon system and we find that it is sensitive to parameter space at and below the seesaw floor, $|V_{\ell N}|^2 \approx 10^{-12}$ ($\ell = e$, $\tau$) for $m_N \approx 40$ GeV. With existing data constraining such well-motivated scenarios of neutrino mass generation, we determine the projected sensitivity at the HL-LHC, motivating dedicated searches for long-lived RHNs with decay lengths $\approx 10$ m.