PT Journal AU ATLAS Collaboration (Aad, Gea Cabrera Urban, S Castillo Gimenez, V Costa, MJ Ferrer, A Fiorini, L Fuster, J Garcia, C Garcia Navarro, JE Gonzalez de la Hoz, S Hernandez Jimenez, Y Higon-Rodriguez, E Irles Quiles, A Kaci, M King, M Lacasta, C Lacuesta, VR Marti-Garcia, S Mitsou, VA Moles-Valls, R Oliver Garcia, E Pedraza Lopez, S Perez Garcia-Estañ, MT Romero Adam, E Ros, E Salt, J Sanchez Martinez, V Soldevila, U Sanchez, J Torro Pastor, E Valero, A Valladolid Gallego, E Valls Ferrer, JA Vos, M TI Search for long-lived neutral particles decaying into lepton jets in proton-proton collisions at root s=8 Tev with the ATLAS detector SO Journal of High Energy Physics JI J. High Energy Phys. PY 2014 BP 088 EP 48pp VL 11 IS 11 DI 10.1007/JHEP11(2014)088 LA English DE Hadron-Hadron Scattering AB Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (so-called "lepton jets"). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors' linear dimensions. This paper presents the results of a search for lepton jets in proton-proton collisions at the centre-of-mass energy of root s = 8 TeV in a sample of 20.3 fb(-1) collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle's proper decay length. ER