Measurement of azimuthal asymmetries in neutral current deep inelastic scattering at HERA

TL;DR

This study measures azimuthal asymmetries in neutral current deep inelastic scattering at HERA, revealing that current QCD predictions underestimate the observed asymmetries, indicating the need for higher-order theoretical calculations.

Contribution

It provides the first detailed measurement of azimuthal asymmetries over a broad pseudorapidity range using the energy-flow method in neutral current deep inelastic scattering.

Findings

Next-to-leading-order QCD better describes data than leading-log models

Predicted asymmetries are smaller than observed

Higher-order calculations may be needed for accurate modeling

Abstract

The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic $ep$ scattering using an integrated luminosity of 45 pb-1 taken with the ZEUS detector at HERA. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data.