Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb-Au collisions at 158 A GeV/c

Azimuthal correlations of hadrons with high transverse momenta serve as a measure to study the energy loss and the fragmentation pattern of jets emerging from hard parton-parton interactions in heavy-ion collisions. Preliminary results from the CERES experiment on two- and three-particle correlations in central Pb-Au collisions are presented. A strongly non-Gaussian shape on the away-side of the two-particle correlation function is observed, indicating significant interactions of the emerging partons with the medium. Mechanisms like deflection of the initial partons or the evolution of a mach cone in the medium can lead to similar modifications of the jet structure on the away-side. An analysis based on three-particle correlations is presented which helps us to shed light on the origin of the observed away-side pattern