Measurement of the tt̄+≥1b-jet cross section using novel multivariate analysis techniques at the CMS experiment

This thesis provides a measurement of the signal strength and cross section for the production of a top quark-antiquark pair in association with one or more jets with a bottom hadron (tt̄+≥1b-jet), while employing neural networks as multivariate analysis method in such a measurement for the first time. In addition to the neural network analysis the tt̄+≥1b-jet signal strength and cross section is also determined by using a simpler B-jet multiplicity based analysis acting as a baseline analysis and a linear discriminant based analysis, which was used as a cross check of the neural network based analysis. Furthermore, a simultaneous measurement of the tt̄+bb̄ signal strength and cross section, the tt̄+2b signal strength and cross section, and the tt̄+b signal strength and cross section is presented in this thesis. These three processes are subsummed under the term tt̄+≥1b-jet processes. In similar fashion, a simultaneous measurement of the tt̄+≥1b-jet signal strength and cross section and the signal strength and cross section of the associated production of top quark- antiquark pairs and a Higgs boson (tt̄H) was conducted and its results are given. Moreover, a study of a possible improvement of the tt̄+≥1b-jet modeling by Monte Carlo event generators is presented.