Measurement of the charged-current Drell-Yan single- and double-differential cross-sections at high transverse masses at $\sqrt{s}=13\,\text{TeV}$ with the ATLAS detector

In this thesis, the measurement of the single- and double-differential cross-sections for the charged-current Drell-Yan process in the leptonic decay into an electron and an electron neutrino, $q\bar{q} \to W \to e\,\nu_e$, is presented. The analysed dataset is recorded by the ATLAS experiment at the Large Hadron Collider during $pp$-collisions of the full Run 2 at a centre-of-mass energy of $\sqrt{s}=13\,\text{TeV}$. In contrast to former measurements, where the cross-section at the peak of the W boson mass is measured, this thesis focuses on $W$ boson masses up to $\mathcal{O}(1\,\text{TeV})$, where the cross-sections are measured for the first time. One of the key ingredients for this measurement is the estimation of the multijet background, originating from fake electrons. The multijet background is estimated based on the data-driven Matrix Method. Occurring issues of data-driven methods that depend on the transverse missing momentum are described and a corresponding systematic uncertainty is assigned. Another crucial aspect is the unfolding of the analysed dataset in a phase space, where a high amount of migrations is expected. The measured data distribution is unfolded to the born level using the Iterative Bayesian Unfolding. Its iterative procedure is well-suited to correct bin-by-bin migrations. The single-differential cross-section as a function of the transverse mass of the W boson, $m_\text{T}^W\in [200,2000]\:\text{GeV}$, and the double-differential cross-section as a function of the transverse mass of the W boson and the absolute value of the electron's pseudorapidity, $m_\text{T}^W \otimes |\eta|\in [200,2000]\:\text{GeV}\otimes[0.0, 2.4]$, are presented. The differential cross-sections for both charges of the $W$ boson, i.e. in the $e^+$ and $e^-$ channel, are measured separately. The corresponding statistical and systematic uncertainties are reported as well. The unfolded single- and double-differential cross-sections are compared to the theoretical prediction from $\texttt{POWHEG BOX V1}$ and $\texttt{PYTHIA 8}$, where an overall reasonable agreement within the uncertainty is found.