Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector

A search is conducted for a new scalar boson S, with a mass distinct from that of the Higgs boson, decaying promptly 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 150 and 1500 GeV. The search uses proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider (LHC) with an integrated luminosity of 139 fb-1 at a centre-of-mass energy of sqrt(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 the branching ratio, σ(pp→S)×B(S→ZdZd)×B^2(Zd→ℓℓ), as a function of the masses of the S and Zd bosons.