Searching for heavy neutral leptons through exotic Higgs decays at the ILC

Abstract

In this study we investigate the feasibility of detecting heavy neutral leptons (Nd) through exotic Higgs decays at the proposed International Linear Collider (ILC), specifically in the channel of e+e−→qqH with H→νNd→νlW→νlqq. Analyses based on full detector simulations of the ILD are performed at the center-of-mass energy of 250 GeV for two different beam polarization schemes with a total integrated luminosity of 2 ab−1. A range of heavy neutral lepton masses between the Z boson and Higgs boson masses are studied. The 2σ significance reach for the joint branching ratio of BR(H→νNd)·BR(Nd→lW) is about 0.1%, nearly independent of the heavy neutral lepton masses, while the 5σ discovery is possible at a branching ratio of 0.3%. Interpreting these results in terms of constraints on the mixing parameters |ϵid|2 between SM neutrinos and the heavy neutral lepton, it is expected to have a factor of 10 improvement from current constraints. Published by the American Physical Society 2024