CONSTRAINTS ON ISOSPIN BREAKING IN THE LIGHT QUARK SEA FROM THE DRELL-YAN PROCESS

One possible interpretation of recent deep inelastic scattering data applied to the Gottfried sum rule is that SU(2) isospin symmetry is violated in the light quark sea in the proton, i.e., uBAR not-equal dBAR. The data can equally well be described by retaining SU(2) symmetry but postponing the onset of Regge behavior to much smaller x values than are currently sampled experimentally. We show how the Drell-Yan process can provide definitive, discriminating information on this issue. We suggest a new Drell-Yan experiment, which should prove decisive, and show how existing data may already rule out the isospin-breaking hypothesis.