Combination of searches for invisible Higgs boson decays with the ATLAS experiment

Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This document presents a statistical combination of searches for the resulting $H\to\text{invisible (inv)}$ decays where $H$ is produced according to the Standard Model via vector boson fusion, $Z(\ell\ell)H(\text{inv})$, and $W\!/\!Z(\text{had})H(\text{inv})$, all performed with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt s = 13$ TeV at the LHC. In combination with the results at $\sqrt s = 7$ and 8 TeV, an exclusion limit on the $H\to\text{inv}$ branching ratio of $\mathcal B_{H\to\text{inv}} < 0.26~(0.17^{+0.07}_{-0.05})$ at 95% confidence level is observed (expected).