HARD QCD IN ATLAS

The production of photon-pairs, W/Z bosons and jets in proton-proton ($pp$) collisions at the LHC allows to probe perturbative QCD in extreme regions of the phase space. Precise measurements are essential to increase the knowledge of Parton Distribution Functions (PDFs), to tune predictions and to improve Monte Carlo simulations. In this paper, recent precision measurements of di-photon production, Z-boson production in association with jets and the fragmentation properties of b-quark initiated jets, performed using data collected by the ATLAS experiment at 13 TeV, are presented. Fits to determine PDFs using hard QCD measurements from ATLAS at various center-of-mass energies ($\sqrt{s}$) together with HERA data are also shown.