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Top Quark Physics at the LHC

Final Report Summary - TOP@LHC (Top Quark Physics at the LHC)

The top quark is one of the most recently discovered sub­atomic particles, and will be intensively studied at the forthcoming Large Hadron Collider at CERN, Geneva. Due to the large mass of the this particle, it is widely hoped that effects of new physics (i.e. beyond the Standard Model of particle physics) will show up in the top quark sector. Thus, measurements of top quark behaviour have the potential to revolutionise our understanding of fundamental physics. Efficient scrutiny necessitates the development of sophisticated theoretical tools, which calculate how the top quark behaves both within and beyond the Standard Model. This has been the focus of the project TOP@LHC, and the researcher has achieved the following goals:

(a) The implementation of the Wt scattering process (in which a top quark is made in association with a W boson) in the MC@NLO software framework. This is a general purpose computer code designed to interface theoretical calculations of top quark behaviour with an algorithm designed to model the effects of a real experiment. The MC@NLO code for top quark production completes the description of single top production modes in this framework, and provides the state of the art for modelling such processes. The software has a potentially wide application in the experimental particle physics community and example results are shown in figure 2.1.

(b) A detailed study of the feasibility of measuring Wt production at the LHC. The theoretical description of this process is potentially undermined by quantum interference effects (i.e. with top quark pair production, whose scattering cross­section is much larger). An in­depth analysis is required and has been carried out, showing that one may be confident of measuring the Wt process. Furthermore, the MC@NLO description has been shown to be accurate in a different context, that of modelling the Standard Model background to Higgs boson production with subsequent decay to a pair of W bosons. The Higgs boson is a currently undiscovered particle used within the Standard Model to explain the origin of mass. It is hoped that the LHC will discover this particle, and this decay mode offers the only hope of discovery if the mass of the particle lies within a certain range. Accurate modelling of top quark backgrounds is needed in order to be certain that a Higgs signal has been found.

(c) The implementation of the H­ t process (in which a single top quark is produced in association with a charged Higgs boson) within the MC@NLO software framework. This is an important scattering process, given that charged Higgs bosons do not occur within the Standard Model, but generically occur in extensions to it (such as supersymmetry), which are widely hoped to appear at the LHC. Again, the MC@NLO software provides the state of the art in describing such processes, and can be used to develop and test strategies for finding the new particle if it exists.