Measurement ofe+e−Asymmetry in Deep-Inelastic Bremsstrahlung

We have measured $\frac{(e^{+}p\to e^{+}\gamma X)}{(e^{-}p\to e^{-}\gamma X)}=1.080\mathrm{}\pm 0.036$ in the scaling region, despite our finding $e^{+}$ and $e^{-}$ total inelastic scattering to be the same to the $\frac{1}{3}\%$ level. The magnitude and sign of the difference signal are consistent with the parton model, from which we extract a mean sum of cubes of parton charges in the proton, $〈\Sigma i^{}{Q_i}^3〉=0.89\mathrm{}\pm 0.34$. Statistics are insufficient to distinguish between fractional ($〈\Sigma i^{}{Q_i}^3〉=0.56\mathrm{}$) and integral charge ($〈\Sigma i^{}{Q_i}^3〉=1, or 0.78$ for colored quarks).