Speaker
Description
The greatest achievement of the LHC is the discovery of the Higgs boson in 2012. Testing the properties of this newly discovered particle represents a crucial task in the understanding of the fundamental laws of nature. Very important is to study how the Higgs boson couples to another exotic particle, the top quark. This can be done studying the process where the Higgs boson is produced in association with a top-quark pair ($t\bar{t}H$). This process represents only $1\%$ of the total Higgs boson production rate. However, it allows to directly probe the top-quark Yukawa coupling. This study can be performed in various decay channels of the Higgs boson, for instance $t\bar{t}H (H \rightarrow b\bar{b})$. This is of course not a simple task, since these events are buried below a considerable amount of background events. Therefore, to correctly characterize this signature, one needs to properly describe the background. In my presentation I will investigate the $t\bar{t}b\bar{b}$ production at the LHC, which represents an irreducible background to $t\bar{t}H (H \rightarrow b\bar{b})$. This study has been performed in the dileptonic decay channel of the top quark with NLO QCD accuracy, both with full off-shell effects (namely without any approximation) and in the Narrow Width Approximation (where the heavy resonances are produced on-shell and then decayed). Then, I will show a comparison between these theoretical predictions and experimental results recently obtained by the ATLAS collaboration. I will also investigate the nature of the $b$-jets present in the process and provide a prescription to label them in order to better characterize the background.
