We have performed the measurement of the cosmic ray muon charge ratio, as a
function of the muon momentum, using data collected by the CMS experiment,
exploiting the capabilities of the muon barrel drift tube (DT) chambers. The
cosmic muon charge ratio is defined as the ratio of the number of positive- to
negative-charge muons. Cosmic ray muons result from the interaction of
high-energy cosmic-ray particles (mainly protons and nuclei), entering the
upper layers of the atmosphere, with air nuclei. Since these collisions favour
positive meson production, there is an asymmetry in the charge composition and
more positive muons are expected.
The data samples were collected at the \textit{Magnet Test and Cosmic
Challenge} (MTCC). While the MTCC itself was a crucial milestone in the CMS
detector construction, not having physics studies among its primary goals, it
provided the first opportunity to obtain physics results and test the full
analysis chain using real data in CMS before the LHC startup, together with a
complementary check of the detector performance.Comment: Poster at ICHEP08, Philadelphia, USA, July 2008. 4 page
