Measurement of the Drell-Yan Differential Cross Section with the CMS Detector at the LHC

This thesis describes precision measurements of electroweak interactions in a new energy regime and the application of these measurements to improve our understanding of the structure of the proton. The results are based on proton-proton collision data at √s = 7 and 8 TeV recorded with the Compact Muon Solenoid detector at the CERN Large Hadron Collider during the first years of operation. Measurements of the differential Drell-Yan cross section in the dimuon and dielectron channels covering the dilepton mass range of 15 to 2000 GeV and absolute dilepton rapidity from 0 to 2.4 are presented. The Drell-Yan cross section in proton-proton collisions depends on empirical quantities known as parton distribution functions (PDFs) which parameterize the structure of the proton. In addition to the differential cross sections, the measurements of ratios of the normalized differential cross sections (double ratios) at √s = 7 and 8 TeV are performed in order to provide further constraints for PDFs, substantially reducing theoretical systematic uncertainties due to correlations. These measurements are compared to predictions of perturbative QCD at the next-to-next-to-leading order computed with various sets of PDFs. The measured differential cross section and double ratio in bins of absolute rapidity are sufficiently precise to constrain the proton parton distribution functions. The inclusion of Drell-Yan data in PDF fits provides substantial constraints for the strange quark and the light sea quark distribution functions in a region of phase space which has not been accessible at hadron colliders in the past.