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.
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Moreover, a study of a possible improvement of the tt̄+≥1b-jet modeling by Monte Carlo
event generators is presented.