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 ZB 0 Z8 0 ZR 0 ZS 0

Search for Invisible Decays of a Higgs Boson Produced in Association with a Z Boson in ATLAS

CAPUA, Marcella;Crosetti G.;LA ROTONDA, Laura;MASTROBERARDINO, Anna;Meoni E.;