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The first determination of the strong coupling constant alpha_s via the differential 2-jet-rate in pp collisions at the LHC (at a center-of-mass-energy of 7 TeV) is presented. Data gathered by the ATLAS experiment are fitted by next-to-leading order (NLO) perturbative QCD predictions from calculations with the program NLOJET++. As an observable, the jet-flip-parameter from 3 to 2 reconstructed jets is investigated, using the infrared and collinear safe kT jet algorithm in the exclusive reconstruction mode. The jet-flip-parameters from real data are compared to simulated data from Monte Carlo generators. For the determination of alpha_s, real data have been corrected for the jet-energy-scale, whereas the calculations from NLOJET++ have been corrected for the influence of hadronization effects as well as the impact of the Underlying Event by applying bin-by-bin corrections. The fit between real data and the calculations from NLOJET++ yields a value of alpha_s(M_Z) = 0.120ñ0.001(stat.)ñ0.005(syst.), which is in very good agreement with the current world average.

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Dr. rer. nat. Markus Lichtnecker was born in the year 1984. He studied Physics at the Ludwig-Maximilians-Universität in Munich, Germany. After his diploma he did his PhD at the LMU with researches at CERN, Switzerland.

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