Measurement of isolated-photon plus jet production in $pp$ collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector at the LHC

The study of the production of prompt photons in association with hadronic jets provides a test of perturbative Quantum Chromodynamics and gives information on the proton parton distribution functions. The colorless prompt photon represents a clean probe of the hard partonic interaction since the photon is produced in the hard scattering and does not undergo hadronization. The measurement of the angular correlations between the photon and the hadronic jets is a test of perturbative Quantum Chromodynamics at large hard scattering scales and over a large range of proton momentum fraction. In this thesis, the dynamics of isolated-photon production in association with a jet in proton-proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the Large Hadron Collider using a dataset with an integrated luminosity of 3.2 fb$^{-1}$. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti-$\mathrm{k_t}$ algorithm with radius parameter R = 0.4 and are required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements.