Abstract
Abstract:
A search for an invisibly decaying Higgs boson or dark matter candidates produced in asso- ciation
with a leptonically decaying Z boson in proton–proton collisions at √s = 13 TeV is
presented. This search uses 36.1 fb−1 of data collected by the ATLAS experiment at the Large Hadron
Collider. No significant deviation from the expectation of the Standard Model backgrounds is
observed. Assuming the Standard Model ZH production cross-section, an observed (expected) upper
limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of
the Higgs boson with mass mH = 125 GeV. The cor- responding limits on the production cross-section
of the ZH process with the invisible Higgs boson decays are also presented. Furthermore, exclusion
limits on the dark matter candidate
and mediator masses are reported in the framework of simplified dark matter models.