Phenomenological constraints on the flavour asymmetry of the nucleon sea

We study the possible flavour asymmetry, ū 6= d̄, of the light quark sea distributions of the proton. We discuss the information that is at present available from data on deep-inelastic lepton-nucleon scattering and from DrellYan production on various nuclear targets. We show that the ratio of dilepton yields on hydrogen and deuterium targets is very sensitive to ū − d̄. The increased precision of deep inelastic lepton-nucleon scattering data has considerably improved our knowledge of the parton distributions of the proton. Until recently all global structure function analyses assumed that the light quark sea distributions satisfied the equality ū = d̄. However, motivated by the improvement of the data, particularly at small x, and by the consequences for the Gottfried sum rule, analyses [1, 2, 3] have been performed with ū 6= d̄. Here we wish to explore how large an inequality the available data can tolerate and to see how well future experiments can pin down ū− d̄. Valuable insight into the problem is obtained by expressing (to leading order) the observed muon and neutrino deep inelastic structure functions in terms of the parton densities F μp 2 − F μn 2 = 1 3x(u+ ū− d− d̄) (1)