Measurement of Azimuthal Asymmetries in Deep Inelastic Scattering
ZEUS Collaboration
TL;DR
This study measures azimuthal asymmetries in neutral-current deep inelastic scattering of positrons on protons with the ZEUS detector at HERA, focusing on the φ distribution of charged hadrons in the hadronic c.m.s. The distribution is modeled as dσ/dφ = A + B cos φ + C cos 2φ, allowing separation of non-perturbative and perturbative QCD contributions. The data reveal a non-zero ⟨cos 2φ⟩ that grows with hadron transverse momentum, consistent with perturbative QCD (QCD-Compton and boson-gluon fusion), while ⟨cos φ⟩ has both perturbative and non-perturbative components, especially at lower p_c. Comparisons with Monte Carlo generators and LO QCD calculations indicate that perturbative effects dominate the cos 2φ term, providing a clean test of QCD dynamics in DIS azimuthal correlations.
Abstract
The distribution of the azimuthal angle for the charged hadrons has been studied in the hadronic centre-of-mass system for neutral current deep inelastic positron-proton scattering with the ZEUS detector at HERA. Measurements of the dependence of the moments of this distribution on the transverse momenta of the charged hadrons are presented. Asymmetries that can be unambiguously attributed to perturbative QCD processes have been observed for the first time.