The W Charge Asymmetry: Measurement of the Proton Structure with the ATLAS detector

The charge asymmetry in the production of $W^{pm}$ bosons in $pp$ collisions is dependent on the momenta of the partons participating in the Drell-Yan process. It is a sensitive probe in particular to the $u$ and $d$ valence quark distributions, that are only loosely constrained in the kinematic range of the LHC $pp$ collider. A measurement of the $W$ charge asymmetry will be crucial to understand the initial states of $pp$ collisions at the LHC centre of mass energy of $sqrt{s}=$14 TeV. In this thesis a weighting technique to measure the $W$ charge asymmetry at the LHC is evaluated and discarded as not sound in the kinematic range of the collider. Therefore, the prospects of a measurement of the lepton charge asymmetry at $sqrt{s}=14$ TeV with $100,mathrm{pb}^{-1}$ as a function of the pseudorapidity of the lepton are investigated using simulated data of the ATLAS detector. This includes a full and thorough analysis of the systematical errors. For 100 $mathrm{pb}^{-1}$, the expected total percentage errors are found to be between 5-10%. These relative errors are a factor of 0.5-0.8 below the PDF uncertainties, which are about 15% in the kinematic range of the LHC. Hence an early measurement of the $W$ asymmetry will be crucial to put constraints on the PDFs.