How Accurately Can we count the number of $pp \to ZX$ and $pp \to WX$ events using decays to electrons

This note describes an analysis of the reaction pp -> ZX and pp -> WX with Z and W decays to electrons, using the full CMS detector simulation and event reconstruction chain. Inclusive Z and W events with their decays to electrons are selected with robust and essentially background-free criteria. The aim of this analysis is to define some baseline selection such that the potential uncertainties from known detector inhomogeneities can be determined. In absence of sufficiently large di-jet event samples, no detailed background studies could be performed. However, it is known from previous CMS studies that the proposed selection criteria are rather insensitive to background and the "early" miscalibrations. This robust selection can thus be considered as especially useful for the CMS startup phase. Keeping these shortcomings in mind, a Z selection efficiency of about 60% is obtained, if the Z decay products end up within the barrel ECAL acceptance. The corresponding efficiency for W's is about 25%. Gaps between the crystals have been studied and the overall efficiency loss from these gaps has been determined to be about 1%. With the available statistics from the Z Monte Carlo sample, corresponding to 0.2/fb, it appears possible to monitor this loss and other potentially inefficient regions with good accuracy. So far, no obstacle has been found which excludes the goal to obtain an accuracy of 1% for the efficiency corrected number of centrally produced Z -> e+e- and W -> e nu events.