Study of the isospin symmetry breaking in the light quark sea of the nucleon from the Drell-Yan process

Abstract

The ratio of cross-sections for muon pair production through the Drell-Yan process in p − p and p − d reactions has been measured at y ≈ 0, with 450 GeVc incident protons. The asymmetry A DY = δ pp − δ pn δ pp+δ pn amounts to −0.09 ± 0.02 ± 0.025. The ratio u d of the nucleon sea structure functions derived from this measurement amounts to 0.51 ± 0.04 ± 0.05 at x = 0.18 and suggests that isospin symmetry is broken in the light quark sea of the nucleon.