Semi-dark Higgs decays: sweeping the Higgs neutrino floor

TL;DR

This paper investigates exotic Higgs decays into a Z boson and an invisible particle, exploring their potential to reveal new physics beyond the Standard Model at the LHC and ILC.

Contribution

It provides a detailed analysis of semi-dark Higgs decays involving invisible particles, highlighting their detectability and potential to probe new physics parameter spaces.

Findings

Exotic Higgs decays can be detected at the LHC and ILC.

Such decays can explore new regions of ALP and dark matter models.

The SM neutrino background sets a fundamental sensitivity limit.

Abstract

We study exotic Higgs decays $h \to Z X$, with $X$ an invisible beyond the Standard Model (SM) particle, resulting in a semi-dark final state. Such exotic Higgs decays may occur in theories of axion-like-particles (ALPs), dark photons or pseudoscalar mediators between the SM and dark matter. The SM process $h\to Z\nu\bar{\nu}$ represents an irreducible "neutrino floor" background to these new physics searches, providing also a target experimental sensitivity for them. We analyze $h \to Z + \text{invisible}$ searches at the LHC and a future ILC, showing that these exotic Higgs decays can yield sensitivity to unexplored regions of parameter space for ALPs and dark matter models.