Measurement of high-Q2 neutral current deep inelastic e+p scattering cross sections with a longitudinally polarised positron beam at HERA

TL;DR

This paper reports precise measurements of neutral current deep inelastic scattering cross sections with polarized positrons at HERA, confirming Standard Model predictions and exploring parity violation effects.

Contribution

First measurement of neutral current cross sections with polarized positron beams at HERA in the specified kinematic range, including structure functions and parity violation analysis.

Findings

Results agree with Standard Model predictions.

Determined structure functions F3 and F3(gamma)Z.

Demonstrated parity violation through asymmetry parameter A+.

Abstract

Measurements of neutral current cross sections for deep inelastic scattering in e+p collisions at HERA with a longitudinally polarised positron beam are presented. The single-differential cross-sections d(sigma)/dQ2, d(sigma)/dx and d(sigma)/dy and the reduced cross-section were measured in the kinematic region Q2 > 185 GeV2 and y < 0.9, where Q2 is the four-momentum transfer squared, x the Bjorken scaling variable, and y the inelasticity of the interaction. The measurements were performed separately for positively and negatively polarised positron beams. The measurements are based on an integrated luminosity of 135.5 pb-1 collected with the ZEUS detector in 2006 and 2007 at a centre-of-mass energy of 318 GeV. The structure functions F3 and F3(gamma)Z were determined by combining the e+p results presented in this paper with previously published e-p neutral current results. The asymmetry parameter A+ is used to demonstrate the parity violation predicted in electroweak interactions. The measurements are well described by the predictions of the Standard Model.