Master thesis Defense by Bjørn Peter Sørensen – University of Copenhagen

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Master thesis Defense by Bjørn Peter Sørensen

Master thesis Defense by Bjørn Peter Sørensen

Title: Measurement of the W-Boson Mass with the ATLAS detector at LHC

Abstract: This analysis is a first attempt at a W boson mass measurement at the LHC. The measurement is based on the W μ events from 827 pb−1 proton collisions at7 TeV collected with the ATLAS detector in the first half of 2011, when the pileupof other protons collisions in the same event were minimal. Using MC templatesfor various W-masses of the transverse muon momentum, high sensitivity to theW mass is obtained.Z μμ events are used as calibration for the muon pT scale, but the systematicuncertainties from other sources are still dominant compared to the muonpT -scale and statistical uncertainty. The largest source of uncertainty is due topileup events which degrades the resolution on missing transverse energy. This inturn biases the event selection and increases the amount of QCD background.My final measurement of the W boson mass is MW = 80.510±0.032±0.060 GeV. 

Supervisor: Troels C. Petersen