Measurement of the WbWb cross-section in the dilepton channel using classical and quantum computing techniques with the ATLAS detector at the LHC

The top quark is the heaviest known elementary particle of the Standard Model. Thanks to its particular properties, it allows to explore unique physics domains, inaccessible otherwise: one of them is the $WbWb$ production from proton-proton collisions. Studying this process is very important for a better knowledge of the Standard Model, but also to investigate some Beyond the Standard Model phenomena. In this work, the first ever measurement of the fiducial differential cross-sections of the $WbWb$ production in the dilepton channel is provided. The measurement is performed using the full dataset collected by the ATLAS detector from proton-proton collisions at the LHC during Run-2 at $\sqrt{s}=\SI{13}{\tera\electronvolt}$ corresponding to an integrated luminosity of $\SI{140}{\femto\barn^{-1}}$. The differential cross-sections have been measured as a function of kinematic variables characterizing the $WbWb$ final states and one $t\bar{t}/tW$ interference-sensitive variable, defined as $m_{bl}^{\text{minimax}}$. The results are then compared to several Monte Carlo predictions. We have also developed a novel unfolding method based on quantum annealing, along with a dedicated software tool, called \texttt{QUnfold}. Our implementation is the first LHC-size data analysis software capable of using quantum computation to solve the unfolding problem and therefore to measure differential cross-sections of particle physics processes. We successfully tested it on the $WbWb$ ATLAS data used for the main analysis of this work.