The distribution of the azimuthal angle for the charged hadrons has been st
udied in the hadronic centre-of-mass system for neutral current deep inelas
tic positron-proton scattering with the ZEUS detector at HERA. Measurements
of the dependence of the moments of this distribution on the transverse mo
menta of the charged hadrons are presented. Asymmetries that can be unambig
uously attributed to perturbative QCD processes have been observed for the
first time. (C) 2000 Elsevier Science B.V. All rights reserved.