Isolated direct photon production and the Atlantis event display for the ATLAS experiment.

A study of the possibilities for a direct photon cross-section measurement is carried out, in the context of expectations for the first LHC collision data from the ATLAS experiment. Comparisons are made between Monte-Carlo predictions and an optimised method of selecting and reconstructing the events from data taken by the detector is described. Also explained is work carried out on the Atlantis event display. The thesis begins with a general overview of current research in particle physics, motivating the building of the LHC and ATLAS. These are described, concentrating on the main motivations for a direct photon measurement. The Atlantis software is described next, explaining its role in ATLAS and some of its features. This is followed by a more detailed description of the work carried out on improving the existing Atlantis features and expanding the scope of the project. Following this the steps required in making a direct photon cross-section measurement are laid out, beginning with a theoretical discussion of what direct photons are and why they are interesting to study. Studies carried out with different Monte-Carlo simulations are described. The methods used for trigger, photon and jet reconstruction are laid out along with cuts that can be applied to select pure photon samples. The final generator and reconstruction selections are then laid out step by step in the final chapter, which finishes with an assessment of the achievable precision on the differential cross-section.