Measurement of the top quark pair production cross section with the ATLAS experiment at ps = 7TeV
- Autores: Volker Vorwerk
- Directores de la Tesis: Aurelio Juste Rozas (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2011
- Idioma: inglés
- Tribunal Calificador de la Tesis: Enrique Fernández (presid.), Juan Antonio Aguilar Saavedra (secret.), Markus Cristinziani (voc.)
- Enlaces
- Resumen
The production cross section of top quark pairs with a semi-leptonic final state was measured in proton-proton collisions at ¿s = 7 TeV with the ATLAS experiment at the LHC. A first measurement was performed with data corresponding to an integrated luminosity of 2.9 pb-1 , collected during the early running phase of the LHC. Large efforts were made in order to cope with the low statistics and the restricted understanding of the detector at the early stage of the experiment. Events with exactly one electron and muon, high missing transverse energy and exactly three or four and more jets were analyzed. Flavor tagging algorithms were used to further increase the purity of the signal in the final selection sample, requiring at least one jet to originate from a b quark. The production cross section was extracted from a maximum likelihood fit to the invariant mass spectrum of the hadronically decaying top quark candidate, yielding 130 ± 44 (stat.) +34/-28 (syst.) +16/-13 (lumi.) pb. The analysis was improved using the complete data corresponding to 35 pb-1 recorded with the ATLAS detector in 2011. A profile likelihood fit was performed making use of nuisance parameters. That allowed the data to constrain and decrease the systematic uncertainties on the measurement. This motivated a further breakdown into 18 channels with exactly three, exactly four and at least five jets and no, exactly one, and at least two b-tagged jets for the combination of the electron and muon channel. For the improved analysis a top quark pair production cross section of 156 +20/-18 (stat.+syst.) ± 5 (lumi.) pb was measured, representing one of the most precise measurements to date.
