W mass measurement and simulation of the Transition Radiation Tracker at the ATLAS experiment – Niels Bohr Institute - University of Copenhagen

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W mass measurement and simulation of the Transition Radiation Tracker at the ATLAS experiment

Ph.D. defense by Esben B. Klinkby

Abstract:

At the time of writing, the final preparation toward LHC startup is ongoing. All the magnets of the machine have been installed and are currently being cooled. Most sub-detectors of the four experiments situated at the LHC ring are installed in their final positions and are being integrated into their respective data acquisition systems.

This thesis concerns itself with the ATLAS experiment, focusing on a sub-detector called the Transition Radiation Tracker (TRT). Some attention is given to the hardware testing of the detector modules, but the main focus lies on the simulation of the detector and the comparison of the simulation with test-beam data, as well as with data collected during the commissioning phase using cosmic muons.

There is little doubt that LHC will bring insight with respect to the understanding of the universe on the fundamental level. In particular, it is anticipated that light will be shed on the origin of mass which according to our current understanding proceeds via the Higgs mechanism. Either the corresponding particle, the Higgs boson, is discovered by the LHC experiments, or its existence will be strongly disfavoured. In either case, a key measurement to understand the origin of mass is the W boson, since it is closely linked to the Higgs mechanism. By precisely measuring the W boson mass, the allowed mass range for the Higgs boson can be constrained, both within the Standard Model and in its various extensions. Thus, regardless of the results of the Higgs search, a precise determination of the W mass is of paramount importance, and in this thesis methods are presented aiming at measuring the W mass to the highest possible precision with the ATLAS experiment.