Acknowledgements

  To work as a PhD student within particle physics is a teamwork with your results relying on the cooperation of many other people and hopefully with your own results usable by a large amount of people as well. Here I will only mention a few.

First of all, I would like to thank my supervisor Torsten Åkesson who has supported the work all the way along. His time is shared between many projects but still he has managed to guide my work at the right points with his many ideas.

I would like to thank all from the ATLAS TRT collaboration. Step-by-step I was introduced to both hardware and software connected to the testbeam and the general TRT development. In special I would like to thank Daniel Froidevaux and Anatoli Romaniouk. Their constructive criticism of my work has caused a significant improvement of the quality of this thesis.

From the ATLAS physics team I will mention Fabiola Gianotti and Jerome Schwindling who has given advice for my H $\rightarrow$ $\gamma$$\gamma$ analysis. Stephen Haywood also deserves to be mentioned for the great energy he has put into the coordination of physics studies involving the Inner Detector.

From Lund, I would like to thank all my colleagues at the Department of Elementary Particle Physics. The PhD students, Magnus Söderberg, Oxana Smirnova and Helen Korsmo have been great company both in Lund and at CERN. Especially, I will remember many long lunches on the different restaurants in Lund. Torbjörn Sjöstrand from Theoretical Physics has been a great help always ready to help me with the understanding of Higgs physics and its implementation in the PYTHIA event generator.

I am grateful for the funding of my PhD studies from the Swedish Natural Science Research Council and the Danish Research Academy.

Thanks to Sverker Almehed, Daniel Froidevaux, Frank Paige, Anatoli Romaniouk and Torsten Åkesson who have provided comments for different parts of the thesis.

Finally I would like to thank my fiancée Caroline who has been a great support during all four years. I hope no one will ever charge us for the busy internet connection between Lund and Melbourne. I regard is as remarkable that she even took on her the job of proofreading this thesis.