Measurement of the ratios of nu$_{mu}$n to nu$_{mu}$p (n$\overline{u}_{mu}$n to n$\overline{u}_{mu}$p) charged current cross sections at high energies

From the analysis of 5630 nu /sub mu / and of 1372 nu /sub mu / charged current interactions, obtained in the BEBC bubble chamber filled with deuterium and exposed to the CERN wide band antineutrino beam, the ratios of cross sections on neutron and proton targets have been measured and found to be R identical to sigma ( nu approximately /sub n/)/ sigma ( nu approximately )=0.51+or-0.01 (+or-0.03), and R identical to sigma ( nu /sub n/)/ sigma ( nu /sub p/)=2.22+or-0.12 (+or-0.25). The dependence of these ratios on the x scaling variable shows, in a direct way, that the momentum distribution of the majority quark, u/sub p/(x)=d/sub n/(x), is broader than that of the minority quark, u/sub n/(x)=d/sub p/(x). (16 refs).