A New Measurement of the mu+/mu- Ratio at Small Atmospheric Depth

We report on a new measurement of the = ratio at small atmospheric depth in the momentum range 0.3-20 GeV/c using the NMSU-WIZARD/CAPRICE98 balloon-borne magnetic spectrometer. The flight took place on 28-29 May 1998 from Ft. Sumner, New Mexico. In the momentum range 0.3-1 GeV/c the ratio is 1:29 0:08, lower than the corresponding ratio measured in 1994 at Lynn Lake, Canada, which was 1:59 0:06. The difference is attributed to the difference in latitude of the two experiments. For the range 2-20 GeV/c we report a value of the ratio of 1:4 0:1.