Jet physics with the ATLAS experiment at the LHC

A variety of jet measurements are made using data collected during the first year of 7 TeV proton-proton collisions from the general- purpose ATLAS experiment at the LHC. The data are compared to leading-order and next-to-leading order Monte Carlo predictions, which have been interfaced with a parton shower, as well as to next-to-leading order perturbative QCD calculations, which have been corrected for soft effects. In each case, state-of-the-art jet algorithms are used, allowing for a better comparison between data and theory. Two distinct types of analysis are presented in this thesis, mea- surements of jet cross-sections and investigations of QCD emissions in dijet systems. Double differential jet cross-sections, as a function of jet transverse momentum and rapidity or dijet mass and rapidity separation, provide an exacting test of QCD across several orders of magnitude. The study of QCD radiation in dijet systems is performed by vetoing on any QCD activity above a veto scale, Q0 much greater than ΛQCD , permitting the study of a wide range of perturbative QCD phenomena. Less well understood areas of phase space, in which standard event generators have large theoretical uncertainties, can be probed in both widely separated dijet systems and in those with average transverse momenta much greater than the veto scale.