Searches for the leptophilic Z' boson at the International Linear Collider and Linear Collider Facility

Production of the leptophilic Z’ boson at future colliders was proposed as one of the benchmark Beyond the Standard Model (BSM) scenarios for the Physics Briefing Book prepared for the 2026 update of the European Strategy for Particle Physics. Presented in this contributions are results on the sensitivity of the experiments at the International Linear Collider (ILC) and at the Linear Collider Facility (LCF) at CERN to the considered scenario. Studied as a function of the Z’ boson mass is the expected signal in the di-muon decay channel, which is expected to have the highest sensitivity. Signal and background simulation in WHIZARD includes effects of multi-photon emission and initial state radiation (ISR), with proper matching between ISR and matrix element domains. Expected limits on the Z’ couplings to SM leptons are presented for ILC and LCF running at 250 GeV and LCF running at 550 GeV.