Measurement of the charge ratio of cosmic muons using CMS data

This note presents the measurement of the ratio of positive- to negative-charge cosmic muons, performed as a function of the muon momentum, using data collected by the CMS experiment at the \textit{Magnet Test and Cosmic Challenge}. While the magnet test itself is a milestone in the CMS detector construction, not having physics studies among its primary goals, it provides the high quality data --from a large number of cosmic muons-- used in this analysis. This is the first measurement of a physical quantity performed by the CMS experiment.