Probing Heavy Neutrino Magnetic Moments at the LHC using Long-Lived Particle Searches

TL;DR

This paper investigates the potential of LHC long-lived particle searches, specifically non-pointing photons, to detect sterile neutrino magnetic moments, offering sensitivity improvements over previous experiments and insights into new physics.

Contribution

It introduces a novel approach using LLP searches with non-pointing photons to probe sterile neutrino magnetic moments across a wide mass range, surpassing existing constraints.

Findings

LHC LLP searches can probe sterile-to-sterile dipole moments two orders of magnitude below LEP constraints.

Sensitivity to active-to-sterile dipole moments allows detection of neutrinos up to 700 GeV.

Synergy with charged lepton flavor violation searches can explore new physics at several TeV scales.

Abstract

We explore long-lived particle (LLP) searches using non-pointing photons at the LHC as a probe for sterile-to-sterile and active-to-sterile transition magnetic dipole moments of sterile neutrinos. We consider heavy sterile neutrinos with masses ranging from a few~GeV to several hundreds of GeV. We discuss transition magnetic dipole moments using the Standard Model effective field theory and low-energy effective field theory extended by sterile neutrinos ($N_R$SMEFT and $N_R$LEFT) and also provide a simplified UV-complete model example. LLP searches at the LHC using non-pointing photons will probe sterile-to-sterile dipole moments two orders of magnitude below the current best constraints from LEP, while an unprecedented sensitivity to sterile neutrino mass of about 700 GeV is expected for active-to-sterile dipole moments. For the UV model example with one-loop transition magnetic moments, the searches for charged lepton flavour violating processes in synergy with LLP searches at the LHC can probe new physics at several TeV mass scales and provide valuable insights into the lepton flavour structure of new physics couplings.