Tera- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math> stage at future colliders and light composite axionlike particles

The Tera-$Z$ phase of future ${e}^{+}{e}^{\ensuremath{-}}$ colliders, FCC-ee and CEPC, is a gold mine for exploring $Z$ portal physics. We focus on axionlike particles (ALPs) that can be produced via decays with monochromatic photon. As template model, we consider composite Higgs models light pseudoscalar couples through the Wess-Zumino-Witten term to electroweak gauge bosons. For both photophilic photophobic cases, show probe scales up 100s TeV, well beyond capability LHC current precision Our results also apply generic ALPs and, in particular, severely constrain explain muon $g\ensuremath{-}2$ anomaly.