Signatures of Long-Lived Heavy Neutral Leptons from Neutrinophilic Charged Higgs Pair Production at the LHC

TL;DR

This paper explores the potential to detect long-lived heavy neutral leptons produced via neutrinophilic charged Higgs pairs at the LHC, focusing on displaced vertex signatures and their observability.

Contribution

It introduces a new production mechanism for gauge singlet HNLs in the neutrinophilic Higgs framework and analyzes their displaced vertex signatures at the LHC.

Findings

High significance detection of one displaced vertex for cross sections > 1 fb.

Two displaced vertices are difficult to observe even at 10 fb cross section.

Displaced leptons can be identified through dedicated simulation.

Abstract

In the neutrinophilic Higgs doublet framework, the neutrino Dirac Yukawa couplings can be sizable because of the small vacuum expection value of the extra Higgs doublet, even for a low seesaw scale. Due to this structure, the neutrinophilic charged Higgs bosons, once created, decay dominantly into heavy neutral leptons (HNLs) and charged leptons. This is a new mechanism to produce a gauge singlet HNL without suppressed cross sections. In the standard seesaw, one HNL can be long-lived, when the lightest neutrino is sufficiently light. We investigate displaced vertex signatures of the long-lived HNLs produced from the decays of the charged Higgs pair at the high luminosity LHC. We consider one displaced vertex as well as two displaced vertices signatures and perform a dedicated simulation to identify the displaced leptons. We find that high statistical significance can be achieved for the observation of one displaced vertex for charged Higgs pair production cross section $>\mathcal{O}(1)$ fb. On the other hand, the observation of two displaced vertices is challenging even for charged Higgs pair production cross section of $\mathcal{O}(10)$ fb.