Measurement of High-Q^2 Neutral-Current e^+p Deep Inelastic Scattering Cross-Sections at HERA

TL;DR

This paper reports precise measurements of neutral-current e^+p deep inelastic scattering cross-sections at high Q^2 at HERA, confirming Standard Model predictions and providing evidence for Z^0 exchange in space-like interactions.

Contribution

First detailed measurement of high-Q^2 neutral-current e^+p scattering cross-sections at HERA confirming Standard Model predictions.

Findings

Cross-sections decrease by six orders of magnitude from Q^2=400 to 40000 GeV^2

Data agree with Standard Model predictions

Evidence for Z^0 exchange in space-like region

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.