Measurements of Higgs boson properties in the diphoton decay channel with 36.1 fb$^{−1}$ $pp$ collision data at the center-of-mass energy of 13 TeV with the ATLAS detector

Properties of the Higgs boson are measured in the two-photon final state using 36.1/fb of proton-proton collision data recorded at $\sqrt{s}=$ 13 TeV by the ATLAS experiment at the Large Hadron Collider. The ATLAS and CMS mass measurement of $125.09 \pm 0.24$ GeV is used and signals are extracted in a diphoton mass range of 105-160 GeV. Production cross section measurements for a Higgs boson rapidity $|y_H|<$ 2.5 and in the full phase space for gluon fusion (ggH), vector boson fusion (VBF), and Higgs boson production in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed signal yield to the expected signal yield, is measured for the same production processes as well as inclusively. The global signal strength measurement of $0.99 \pm 0.14$ improves on the precision of the previous ATLAS measurement by a factor of 2, and ggH (VBF) production is measured to be $1~\sigma$ below ($2~\sigma$ above) the Standard Model expectation. Measurements of simplified template cross sections, designed to measure the different Higgs boson production processes in specific regions of phase space, are reported. The fiducial cross section is measured to be $54.7 \pm 10.2$ fb for a Higgs boson decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity $|\eta|<2.37$, excluding the region $1.37 < |\eta|<1.52$. Fiducial regions probing Higgs boson production in vector boson fusion or in association with large missing transverse energy, leptons or top-quark pair are reported. Finally, differential cross sections dominated by ggH production are measured as a function of diphoton kinematic variables sensitive to quantum chromodynamics and the spin of the Higgs boson. These are compared with state-of-the-art Standard Model predictions, where no significant deviations are observed.