Abstract
In summer 2008 the world largest proton-proton storage ring, the Large Hadron Collider (LHC), at CERN close to Geneva (Switzerland) will go into service. With a collision energy of 14 TeV the production cross section for top/antitop quarks (t anti t) is about 830 pb (NLO). The top quarks almost exclusively decay into a W boson and a b quark via the weak interaction. In about 44.4% of all events one of the top quarks decays into a lepton and neutrino while the other one decays into two light quarks (semileptonic decay chain). This channel therefore provides a good selection purity (lepton b tagging) and the possibility for the complete reconstruction of the hadronically decaying top quark into three jets. After a short introduction of top quark physics at the LHC and the Compact Muon Solenoid (CMS) detector, this thesis deals with the analyses of top quark reconstruction and mass measurement in two different scenarios. In the first analysis a first physics scenario is taken as a basis where no jet flavour information (e.g. b tagging) and only a reduced detector acceptance region for electron identification is assumed. It is shown that semileptonic top quark pair decays can nevertheless be
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Citation Formats
Kasselmann, S.
Top quark mass measurement in the lepton+jets channel using full simulation of the CMS detector.
Germany: N. p.,
2007.
Web.
Kasselmann, S.
Top quark mass measurement in the lepton+jets channel using full simulation of the CMS detector.
Germany.
Kasselmann, S.
2007.
"Top quark mass measurement in the lepton+jets channel using full simulation of the CMS detector."
Germany.
@misc{etde_21058816,
title = {Top quark mass measurement in the lepton+jets channel using full simulation of the CMS detector}
author = {Kasselmann, S}
abstractNote = {In summer 2008 the world largest proton-proton storage ring, the Large Hadron Collider (LHC), at CERN close to Geneva (Switzerland) will go into service. With a collision energy of 14 TeV the production cross section for top/antitop quarks (t anti t) is about 830 pb (NLO). The top quarks almost exclusively decay into a W boson and a b quark via the weak interaction. In about 44.4% of all events one of the top quarks decays into a lepton and neutrino while the other one decays into two light quarks (semileptonic decay chain). This channel therefore provides a good selection purity (lepton b tagging) and the possibility for the complete reconstruction of the hadronically decaying top quark into three jets. After a short introduction of top quark physics at the LHC and the Compact Muon Solenoid (CMS) detector, this thesis deals with the analyses of top quark reconstruction and mass measurement in two different scenarios. In the first analysis a first physics scenario is taken as a basis where no jet flavour information (e.g. b tagging) and only a reduced detector acceptance region for electron identification is assumed. It is shown that semileptonic top quark pair decays can nevertheless be identified with a signal over background ratio of about S/B=2.4. For this study signal and main background processes using full simulation of the CMS detector have been produced for an integrated luminosity of 0.1 fb{sup -1}. Especially event shape variables are adequate to compensate the missing b jet tagging. The semileptonic channel is the most promising one to rediscover the top quark at the LHC due to the lepton in the final state. In this scenario the needed integrated luminosity has been calculated to be about 2 pb{sup -1} assuming Poisson distributions for the number of signal and background events. A second analysis focusses on the top quark mass measurement in a scenario where the CMS detector is fully equipped and has almost reached its design performance. Therefore data for an integrated luminosity of 1 fb{sup -1} has been analyzed showing that the top quark mass can be reconstructed with a statistical error of about 1 GeV/c{sup 2} and a systematic error of 3.2 GeV/c{sup 2}. The major part of the systematic error is caused by the calibration uncertainty of the hadronic calorimeter. A challenging task in this analysis is the determination of the right three jets coming from the top quark decay among at most five jets. To solve this problem a likelihood ratio method has been developed, which is able of determining the right top quark among up to 17 possible three jet combinations with a purity of up to 64%. It turned out that the physics background is almost negligible and that the intrinsic combinatoric background is dominant. (orig.)}
place = {Germany}
year = {2007}
month = {Nov}
}
title = {Top quark mass measurement in the lepton+jets channel using full simulation of the CMS detector}
author = {Kasselmann, S}
abstractNote = {In summer 2008 the world largest proton-proton storage ring, the Large Hadron Collider (LHC), at CERN close to Geneva (Switzerland) will go into service. With a collision energy of 14 TeV the production cross section for top/antitop quarks (t anti t) is about 830 pb (NLO). The top quarks almost exclusively decay into a W boson and a b quark via the weak interaction. In about 44.4% of all events one of the top quarks decays into a lepton and neutrino while the other one decays into two light quarks (semileptonic decay chain). This channel therefore provides a good selection purity (lepton b tagging) and the possibility for the complete reconstruction of the hadronically decaying top quark into three jets. After a short introduction of top quark physics at the LHC and the Compact Muon Solenoid (CMS) detector, this thesis deals with the analyses of top quark reconstruction and mass measurement in two different scenarios. In the first analysis a first physics scenario is taken as a basis where no jet flavour information (e.g. b tagging) and only a reduced detector acceptance region for electron identification is assumed. It is shown that semileptonic top quark pair decays can nevertheless be identified with a signal over background ratio of about S/B=2.4. For this study signal and main background processes using full simulation of the CMS detector have been produced for an integrated luminosity of 0.1 fb{sup -1}. Especially event shape variables are adequate to compensate the missing b jet tagging. The semileptonic channel is the most promising one to rediscover the top quark at the LHC due to the lepton in the final state. In this scenario the needed integrated luminosity has been calculated to be about 2 pb{sup -1} assuming Poisson distributions for the number of signal and background events. A second analysis focusses on the top quark mass measurement in a scenario where the CMS detector is fully equipped and has almost reached its design performance. Therefore data for an integrated luminosity of 1 fb{sup -1} has been analyzed showing that the top quark mass can be reconstructed with a statistical error of about 1 GeV/c{sup 2} and a systematic error of 3.2 GeV/c{sup 2}. The major part of the systematic error is caused by the calibration uncertainty of the hadronic calorimeter. A challenging task in this analysis is the determination of the right three jets coming from the top quark decay among at most five jets. To solve this problem a likelihood ratio method has been developed, which is able of determining the right top quark among up to 17 possible three jet combinations with a purity of up to 64%. It turned out that the physics background is almost negligible and that the intrinsic combinatoric background is dominant. (orig.)}
place = {Germany}
year = {2007}
month = {Nov}
}