Combined measurements of the Higgs boson production and decay rates in $H\to ZZ^*\to 4\ell$ and $H\to\gamma\gamma$ final states using $pp$ collision data at $\sqrt{s}=$ 13 TeV in the ATLAS experiment

This note presents combined measurements based on Higgs boson production cross sections and branching ratios using more than 13.3 fb$^{-1}$ of proton-proton collision data recorded by the ATLAS experiment at the LHC at $\sqrt{s}=$ 13 TeV. The combination is based on the analyses of the $H\to\gamma\gamma$ and $H\to ZZ^*\to 4\ell$ decay channels. Results are derived for these two decay modes and five sets of production processes for a Higgs boson rapidity $|y_H| < 2.5$ and for a Higgs boson mass of $125.09 \pm 0.21{\rm (stat)} \pm 0.11{\rm (syst)}$ GeV. The global signal strength, defined as the ratio in the full phase space (including $|y_H| \geq 2.5$) between the observed total signal yield and the Standard Model expectation, is measured to be $\mu = 1.13\,^{+0.18}_{-0.17}$. The cross section of $pp \to H + X$ in the full phase space is determined from fiducial cross section measurements to be $59.0^{+9.7}_{-9.2} ~(\mathrm{stat.})~ ^{+4.4}_{-3.5} (\mathrm{syst.})$ pb, to be compared with the Standard Model prediction of $55.5^{+2.4}_{-3.4}$ pb. No significant deviation from the Standard Model expectations is observed.