January 12, 2021 Master Thesis Open Access

Pfeffer, Emanuel

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    <subfield code="a">&lt;p&gt;In this thesis, the interplay of two elementary particles of the SM, the two heaviest quarks top (t) and bottom (b), is studied in detail. Processes in which a top quark-antiquark pair occurs in associated production with two bottom quarks (tt+bb)&amp;nbsp;play an important role in particle physics. The two quarks show a high mass difference and their associated production is therefore particularly difficult to model, accompanied by large uncertainties [6]. In addition, events involving this process constitute a large irreducible background in measurements of tt+H production in H&amp;nbsp;&amp;rarr;&amp;nbsp;bb&amp;nbsp;decays. These measurements are an essential test of the SM and an important constraint of physics beyond the SM. Consequently, the tt+bb&amp;nbsp;process needs to be thoroughly understood.&lt;/p&gt;

&lt;p&gt;Events comprising tt+bb&amp;nbsp;processes are analyzed at two different Monte Carlo event simulation levels in this thesis.&lt;br&gt;
The first part compares different existing event simulations used at the CMS experiment for the tt+bb&amp;nbsp;process in the single-lepton channel and investigates possible differences in the modeling. The analysis is technically realized in a way that allows a direct comparison of the simulations with those of the ATLAS experiment. The comparison of simulations of both experiments is performed building on this analysis. This enables the design of a common strategy between ATLAS and CMS.&lt;/p&gt;

&lt;p&gt;The second part focuses on strategies for assigning b jets to their origin. Since top quarks decay into b quarks almost exclusively, the final state of an event involving the tt+bb&amp;nbsp;process usually consists of four or more b jets. However, it is unknown in the event reconstruction which b jets result from top quark decays and which originate from additional gluon radiation and subsequent splittings into pairs of b quarks in the event.&lt;/p&gt;</subfield>
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