Precision measurements of W and Z boson production and their decays to electrons at hadron colliders

For many measurements at hadron colliders, such as cross sections and branching ratios, the uncertainty of the integratedluminosity is an important contributionto the error of the final result. In 1997, the ETH Zürich group proposeda new approach to determinethe integrated luminosity via a counting measurement of the W and Z bosons throughtheir decays to leptons. In this thesis this proposal has been applied on real data as well as on Simulation for a future experiment. The first part of this thesis describes a dedicated data analysis to precisely mea¬ sure the luminosity at the CDF experimentat the Tevatroncollider (USA) through the production of Z bosons and their decay to electrons. An integrated pp lumi¬ nosity of .Lcounting = 221.7 ± 2.8 (stat.) ± 11.2 (sys.) pb"1 has been measured for the data taking period from March 2002 to February 2004. This is in very good agreement with the traditional measurement at CDF of Lci.c ~ 222.2 ± 12.9 pb-1, using Cherenkov LuminosityCountersat large angles. Bothmeasurements are com¬ plementary and feature systematic uncertainties of similar size. Recent theoretical calculations for the Z production cross section up to next-to-next-to-lcading-order (NNLO) in QCD perturbation theory allow for differential measurements for the first time. These calculations are used for this analysis and a rapidity-dependent lu¬ minosity measurement is presented in addition. The measured rapidity-dependcnee agrecs with the theoretical predictionsfor on-shell Z boson production. The analysis in the second part of this thesis was performedwith Monte Carlo simu¬ lations for the CMS experimentat the future LHC collider at CERN (Switzerland). The goal is to define with the füll detector Simulation a first baseline selection for the Channels pp -» ZX -> ee and pp -^ WX -> eu and to determine potential uncertaintiesfrom detector inhomogeneities. Inclusive Z and W events with their decays to electrons are selected. The robust selection criteria lead to an essentially background-free sample of Z -)¦ e+e" events. The straightforwardselection criteria can be considered as especially useful for the startup phase at CMS. A Z boson selec¬ tion efficiency of approximately60 % is obtained for electrons detected in the central pseudorapidity region of' 1771 < 1.4, and simultaneously a W selection efficiency of about 25 % is obtained. Inactive regions from the gaps between the supermodules of the electromagnetic calorimetcr have been studied and an overall efficiencyloss of roughly 1 % is determined. An integrated luminosity equivalent of about 200 pb"1 of Z —>¦ e+e~ Monte Carlo events have been analyzed. This amount of available statisticsappears to be already sufficient to monitor the losses due to gaps and other potentially inefficient regions. No obstacle has been found which prevents the goal of a 1 % accuracy for counting the efficiency corrected number of centrally produced Z and W events decaying to electrons.