Constraining the Dark Sector with the monojet signature in the ATLAS experiment

This note presents the reinterpretation of the search for final states with at least one energetic jet and missing transverse momentum in the context of dark sector models with long-lived non-charged particles. Results are based on $139\,\mathrm{fb}^{-1}$ of data collected in $pp$ collisions at $\sqrt{s} = 13\,\mathrm{TeV}$ by the ATLAS experiment during Run-2 at LHC. The RECAST software framework is used in this context to probe two different new physics scenarios. Decays of the Standard Model Higgs boson and of a new neutral heavy scalar mediator into long-lived particles are investigated in different channels. The resulting constraints generally extend those from dedicated searches at large proper lifetimes.