Preparation for and measurement of new physics processes using the ATLAS experiment at the LHC

Present-day fundamental physics represents mankind's most ambitious attempt to understand the nature of our Universe. Over the past century, the theories and discoveries of thousands of physicists have culminated in a 'Standard Model' of particles and forces, currently our best description of all that happens in nature. In the Standard Model, matter is made up of lightweight leptons (such as electrons and neutrinos) and quarks. Three forces manipulate these particles: electromagnetism and the weak and strong nuclear interactions. However, the Standard Model does not incorporate gravity - the fourth force. Neither can it explain why the masses of the fundamental particles have the values they do. Furthermore, the Higgs particle, which gives mass to the other fundamental particles, has not yet been observed. It is clear that the Standard Model cannot be the complete picture - it just leaves too many questions unanswered. The hunt is now on to find the ultimate picture of our Universe - the so-called 'theory of everything' - a theory so fundamental, that it fully explains and links together all known physical phenomena. An enormous new particle accelerator - or 'atom smasher' - now being built at the CERN laboratory on the Swiss-French border, is our next, best hope for solving the riddles of the Universe. This accelerator - called the Large Hadron Collider (LHC) - will send protons zooming around a 27km long circular tunnel, 100m underground, at nearly the speed of light. The protons will crash into each other at huge energies, producing showers of subatomic particles. The enormously high energies allow the production of extremely massive particles (which can be seen through Einstein's famous relation E=mc^2). Scientists believe that such particles could have existed in the very first fraction of a second after the birth of the Universe, and that studying them could provide the key to understanding the laws of nature. Several ideas for possible extensions to the Standard Model already exist. One idea - called supersymmetry - predicts that for every particle we know about (such as electrons, photons and quarks) there must also be a much heavier particle - a so-called superpartner. Another possibility is that the LHC will find evidence for the existence of extra dimensions in space. Since we cannot see them or move in them, these dimensions must either be curled up very tightly, or their nature is such that ordinary matter cannot pass into them. The idea that our Universe consists of more than just the three spatial dimensions we're familiar with (left-right, forward-backward, up-down) lives not only in the realms of science fiction, but is a real possibility that many scientists believe would be a crucial step in establishing the 'theory of everything'. Of course, it may be that neither of these ideas is right, and that something else, perhaps something we have not even thought of, lies waiting to be discovered. Either way, the LHC will be able to provide many of the answers we are looking for. I work on ATLAS, one of the LHC experiments that will detect and measure the products of the high-energy proton collisions. When the LHC switches on in less than two years time, I will search for signs of physics beyond the Standard Model. Both supersymmetry and extra dimensions models predict the existence of particles that may not be seen in the experimental apparatus. However, their presence can be inferred by looking for 'missing energy'. Conservation of energy and momentum states that what goes into the experiment should add up to what's left over, after the collision. If it doesn't, this is a signal that we have found something new. The 'missing energy' is often accompanied by streams, or 'jets', of other particles. I will look for signs of new physics by studying processes involving 'jets' and 'missing energy'. The discoveries I make will form the experimental foundations for understanding the fundamental laws of nature.