Probing the dipole portal to heavy neutral leptons via meson decays at the high-luminosity LHC

TL;DR

This paper investigates the potential of future LHC experiments to detect heavy neutral leptons produced via a dipole portal, focusing on meson decays and the resulting long-lived signals.

Contribution

It introduces a novel analysis of HNL detection via the dipole portal at high-luminosity LHC experiments, highlighting their complementary sensitivities.

Findings

FASER2 and FACET can probe new parameter space for HNLs.

Future experiments are especially sensitive to tau neutrino couplings.

Results show improved detection prospects for long-lived HNLs.

Abstract

We consider the dipole portal to sterile neutrinos, also called heavy neutral leptons (HNLs). The dipole interaction with the photon leads to HNL production in meson decays, as well as triggers the HNL decay into an active neutrino and a photon. HNLs with masses of order of 0.01-1 GeV are naturally long-lived if the dipole coupling is sufficiently small. We perform Monte-Carlo simulations and derive the sensitivities of the proposed FASER2 and FACET long-lived particle experiments to HNLs produced via the dipole operator in meson decays at the high-luminosity LHC. Our findings show that these future detectors will be complementary to each other, as well as to existing experiments, and will be able to probe new parts of the parameter space, especially in the case of the dipole operator coupled to the tau neutrino.