Dark axion portal at $Z$ boson factories

TL;DR

This paper explores the phenomenology of the dark axion portal involving Z boson factories, highlighting potential detection methods for axion-like particles through displaced decays and missing energy signatures.

Contribution

It demonstrates that Z boson factories can effectively probe the dark axion portal, especially for heavier dark sector particles with masses above 0.1 GeV.

Findings

Dark axion portal coupling can be sizable at Z boson factories.

Detection prospects are promising for both short and long-lived dark axion particles.

Complementary detection methods enhance the search sensitivity.

Abstract

Dark axion portal connects an axion-like-particle (ALP), which can be the QCD axion, with the SM by the coupling to a photon and a dark photon, leading to a rich and distinct phenomenology related to dark matter, astrophysics, and cosmology. We note that due to the gauge invariance, the $Z$ boson-dark photon-ALP coupling should also be generated with sizable strength, and we study its phenomenological consequences at $Z$ boson factories: LEP, FCC-ee, and forward physics detectors at the LHC and FPF@FCC - FASER and MATHUSLA. Due to the large number of $Z$ bosons produced, DAP particles can be efficiently produced and detected by semi-visible displaced decays of the heavier DS species to $\gamma$+inv. or $f^+ f^-$+inv., and via missing energy signature with zero or one photon. Because of the complementarity of the two approaches, we find great prospects in exploring both short and long-lived lifetime regimes of DAP, especially when the heavier dark species has mass above $0.1\,$GeV.