Azimuthal Asymmetry in Inclusive Hadron Production by $e^{+}{e}^{-}$ Annihilation

We have observed an azimuthal asymmetry in inclusive hadron production by $e^{+}{e}^{-}$ annihilation at the center-of-mass energy $\sqrt{s}=7.4\mathrm{}$ GeV. The asymmetry is caused by the polarization of the circulating beams in the storage ring and allows separate determination of the transverse and longitudinal structure functions. We find that transverse production dominates for $x>\mathrm{}0.2\mathrm{}$ where $x$ is the scaling variable $\frac{2p}{\sqrt{s}}$.