Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-Inelastic Scattering

The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range $0.02<x<0.3$ and 1<Q²<10GeV² for the first time from semi-inclusive deep-inelastic scattering. The quantity [d̄(x)-ū(x)]/[u(x)-d(x)] is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry d̄-ū is found to be nonzero and x dependent, showing an excess of d̄ over ū quarks in the proton.