Measurement of high-$Q^{2}$ neutral-current $e^+p$ deep inelastic scattering cross-sections at HERA

Abstract.

The $e^+p$ neutral-current deep inelastic scattering differential cross-sections $d\sigma/dQ^2$, for $Q^2 > 400$ GeV$^2$, $d\sigma /dx$ and $d\sigma/dy$, for $Q^2 > 400$, 2500 and 10000 GeV$^2$, have been measured with the ZEUS detector at HERA. The data sample of 47.7 pb$^{-1}$ was collected at a center-of-mass energy of 300 GeV. The cross-section, $d\sigma/dQ^2$, falls by six orders of magnitude between $Q^2 =400$ and 40000 GeV$^2$. The predictions of the Standard Model are in very good agreement with the data. Complementing the observations of time-like $Z^0$ contributions to fermion-antifermion annihilation, the data provide direct evidence for the presence of $Z^0$ exchange in the space-like region explored by deep inelastic scattering.