Abstract
A search is conducted for a new scalar boson S, with a mass distinct from that of the Higgs boson, decaying into four leptons (ℓ=e, μ) via an intermediate state containing two on-shell, promptly decaying new spin-1 bosons Zd:S→ZdZd→4ℓ, where the Zd boson has a mass between 15 and 300 GeV, and the S boson has a mass between either 30 and 115 GeV or 130 and 800 GeV. The search uses proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider with an integrated luminosity of 139 fb−1 at a centre-of-mass energy of √s=13 TeV. No significant excess above the Standard Model background expectation is observed. Upper limits at 95% confidence level are set on the production cross-section times branching ratio, σ(gg→S)×B(S→ZdZd→4ℓ), as a function of the mass of both particles, mS and mZd.