Measurement of the ratio of sea to valence quarks in the nucleon

The ratio of sea to valence quarks for nucleons in tungsten has been measured for the fractional momentum range 0.04<$x_N$<0.36. The determination is based on the relative production rate of muon pairs by ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ beams on a tungsten target. The results provide the most accurate determination to date of this ratio in the region $x_N$20 ${\mathrm{GeV}}^2$, and are in good agreement with earlier measurements.