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 into four leptons ($\mathrm{\ell }=$ $e$, $\mu$) via an intermediate state containing two on-shell, promptly decaying new spin-1 bosons $Z_{\text{d}}$: $S\to Z_{\text{d}}{Z}_{\text{d}}\to 4\mathrm{\ell }$, where the $Z_{\text{d}}$ 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 $\sqrt{s}=13$ 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 branching ratio, $\sigma (gg\to S)\times \mathcal{B}(S\to Z_{\text{d}}{Z}_{\text{d}}\to 4\mathrm{\ell })$, as a function of the mass of both particles, $m_S$ and $m_{Z\text{d}}$.