Searches and Phenomenology for New Physics at the ATLAS Experiment

The theoretical description of the smallest constituents of matter, the so-called standard model (SM), agrees with remarkable precision with the very large number of particle physics experiments that have been carried out until today. In spite of this agreement there are still problematic aspects with the SM which make it clear that it will for example not be able to explain physical phenomena at higher energies, which have not been possible to study experimentally up to now. In addition, astronomical observations show that the largest fraction of the mass that affect the motion of the galaxies can not be explained by the matter which is observed. In order to solve these problems additional particles to the ones we know are proposed, which would give rise to phenomena that can only be studied at the experiments built in connection to the 27km long Large Hadron Collider (LHC) at the CERN laboratory in Switzerland. This research project concerns the search for new physics at the ATLAS experiment within the high energy physics group at the University of Cambridge. ATLAS is one of the largest physics experiments ever built and is approximately 45m long, 25m high and weight about 7000 tons. It is designed as a general purpose detector with the ability to study any new physics that acts in the new energy regime available at the LHC. Despite the strong arguments for new physics to appear at the LHC, very little is known about its kind and for this reason it is important to cover all possibilities within the search strategies. This includes for example phenomena originating from new symmetries in nature, extra spatial dimensions, but also possible new phenomena whose origin is not well known. It will take some time after ATLAS starts to collect collision data, at the end of 2009, until the running conditions are stable. For this reason the searches in this project will in a initial phase focus on robust signatures which are suitable for validation of the detector response and the analysis techniques. The scope will then be broadened and the strategies refined with an improved understanding of the detector performance together with larger data volumes. The unknown nature of the new physics also requires that a broad range of theoretical models of new phenomena is available in the simulations tools. In order to conduct the searches efficiently, a detailed understanding of the corresponding processes and how they are described in the simulation will be necessary, in addition to the experimental knowledge. For this reason the proposed research programme couples the searches for new physics tightly with modelling. This work is truly at the frontier of science, probing completely unexplored areas of physics, and it is clear that independent of what will be found at the ATLAS experiment at CERN the knowledge will radically change our understanding of nature at the particle level.