The magnetized MINOS near detector can accurately determine the charge sign
of atmospheric muons, this facilitates a measurement of the atmospheric muon
charge ratio. To reduce the systematic error associated with geometric bias and
acceptance we have combined equal periods of data obtained with opposite
magnetic field polarities. We report a charge ratio of
1.2666±0.0015(stat.)−0.0088+0.0096(syst.) at a mean
Eμ,0cos(θ)=\unit[63]{GeV}. This measurement is consistent with the
world average\cite{Hebbeker}\cite{Haino}\cite{Achard} but significantly lower
than the earlier observation at the MINOS far detector\cite{Adamson}. This
increase is shown to be consistent with the hypothesis that a greater fraction
of the observed muons arise from kaon decay within the cosmic ray shower.Comment: Proceedings for the 2009, 31st International Cosmic Ray Conference in
Lodz Polan