Search for long-lived neutral particles decaying into lepton-jets in 20.3 fb-1 proton-proton collisions at √s = 8 TeV with the ATLAS detector

Several models of elementary particle physics beyond the Standard Model, predict the existence of neutral particles that can decay in jets of leptons and light hadrons (LeptonJets). The results on LeptonJet search with the ATLAS experiment at the proton-proton LHC collider at √s=8 TeV during 2012 data taking (20 fb-1) is presented. No excess of events have been observed over the expected background and the exclusion limits for two different models, that predict the Higgs boson to decay in Lepton-Jets, have been computed. A similar analysis will be performed with the Run II data taking (√s=13 TeV) including other signatures.