Measurement of the double-differential $W\to\mu\nu$ cross-section at high transverse masses at $\sqrt{s}=13\,$TeV with the ATLAS detector

In this thesis, a measurement of differential charged-current Drell-Yan cross-sections at high transverse masses of the $W$ boson is presented. The decay of the $W$ boson to a muon and a muon-neutrino is studied. Proton-proton collisions at the LHC at $\sqrt{s}=13\,$TeV are the basis of the data taken in 2015-2018 with the ATLAS detector, corresponding to an integrated luminosity of $140\,\text{fb}^{-1}$. Single-differential cross-sections as a function of the transverse mass, covering $m_\text{T}^W\in[200,5000]\,$GeV, are presented. Additionally, double-differential cross-sections as a function of $m_\text{T}^W$ and the pseudorapidity of the muon, covering $m_\text{T}^W\in[200,2000]\,$GeV and $|\eta(\mu)|<2.4$, are included. Both measurements are performed separately per $W$-boson charge, and their asymmetry is calculated as well. The number of signal events is unfolded to the Born level. Statistical and systematic uncertainties are included in the results. Overall, the total uncertainty ranges between $\sim3$% and $\sim65$% in the investigated spectra. Born-level theory predictions from simulations using Powheg+Pythia8 and Sherpa2.2.11, respectively, are compared to the unfolded cross-sections. Finally, a combination of the muon-channel measurement performed in this thesis and a parallel electron-channel measurement is presented.