Constraining the Dark Sector with the Mono-jet signature with the ATLAS detector at the LHC

This proceeding is written according to the poster presented at LHCP-2021. A work about 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 neutral particles was there presented. Results are based on139 fb−1of data collected in pp collisions at centre of mass energy of 13 TeV by theATLAS experiment during Run-2 at LHC. Decays of the Standard Model Higgs boson and of anew 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