PT Journal AU ATLAS Collaboration (Aad, Gea Cabrera Urban, S Castillo Gimenez, V Costa, MJ Fassi, F 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 March, L Marti-Garcia, S Miñano, M Mitsou, VA Moles-Valls, R Moreno Llacer, M 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 Villaplana Perez, M Vos, M TI Search for Invisible Decays of a Higgs Boson Produced in Association with a Z Boson in ATLAS SO Physical Review Letters JI Phys. Rev. Lett. PY 2014 BP 201802 - 19pp VL 112 IS 20 DI 10.1103/PhysRevLett.112.201802 LA English AB A search for evidence of invisible-particle decay modes of a Higgs boson produced in association with a Z boson at the Large Hadron Collider is presented. No deviation from the standard model expectation is observed in 4.5 fb(-1) (20.3 fb(-1)) of 7 (8) TeV pp collision data collected by the ATLAS experiment. Assuming the standard model rate for ZH production, an upper limit of 75%, at the 95% confidence level is set on the branching ratio to invisible-particle decay modes of the Higgs boson at a mass of 125.5 GeV. The limit on the branching ratio is also interpreted in terms of an upper limit on the allowed dark matter-nucleon scattering cross section within a Higgs-portal dark matter scenario. Within the constraints of such a scenario, the results presented in this Letter provide the strongest available limits for low-mass dark matter candidates. Limits are also set on an additional neutral Higgs boson, in the mass range 110 < m(H) < 400 GeV, produced in association with a Z boson and decaying to invisible particles. ER