Measurements of the inclusive isolated-photon and photon-plus-jet production in $pp$ collisions at $\sqrt{s} = 13~\mathrm{TeV}$ with the ATLAS detector

Prompt photons with large transverse momenta constitute colourless probes of the hard interaction and their production in proton-proton ($pp$) collisions provides a testing ground for perturbative QCD (pQCD) at large hard-scattering scales ($Q^{2}$) and over a wide range of the incoming parton momentum fraction ($x$). At the LHC, the dominant contribution to prompt-photon production arises from the $qg \rightarrow q\gamma$ process. As a consequence, the production of prompt photons is sensitive to the gluon density in the proton even at the leading order in pQCD. The measurement of the production cross section of inclusive isolated-photons in different ranges of the photon transverse energy and pseudorapidity provides detailed information on the parton distribution functions (PDFs) in different regions of $Q^{2}$ and $x$. The production of prompt photon-plus-jet events also represents an important test of pQCD predictions. Photon-plus-jet events can also be used to calibrate the jet energy scale and its resolution by profiting from momentum conservation in the transverse plane and the accurate measurement of the energy of the photon in the electromagnetic calorimeter. In addition, the measurement of the cross section of photon-plus-jet production in different jet rapidity intervals and angular configurations, depending on the sign of the product of the jet rapidity and photon pseudorapidity, gives access to the PDFs in different regions of $Q^{2}$ and $x$. The results of four different analyses at $\sqrt{s} = 13~\mathrm{TeV}$ are presented: the measurement of the inclusive isolated-photon cross section using $36~fb^{-1}$ of ATLAS data, the measurement of the jet energy scale using in situ techniques in final states in which a jet recoils against a photon, and the measurements of the cross sections for inclusive isolated-photon production and for photon-plus-jet production using the full Run-2 ATLAS luminosity.