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

Energy loss of partons traversing the hot and dense medium in a heavy ion collision can have significant impact on the shape of jets emerging from such collisions. These shapes can be analyzed via azimuthal correlations of a high-pt trigger particle (T) and associated particles (A) in an event. Correlation functions (CF) C2(∆φ) of the difference in the azimuthal angle ∆φ = φT − φA are constructed as the normalized ratio of signaland mixed-event distributions in which triggerand associated particles are taken from different events. In a two-source approach, correlations arising due to the anisotropy of the source in noncentral collisions are subtracted from the measured correlation function. After normalisation to the number of associate pairs per trigger we obtain the conditional yield (CY) 1/N T · dN TA/d(∆φ) as the number of jet-associated particles per trigger. The analysis is based on 3·10 Pb-Au events collected with the CERES-TPC at the CERN-SPS.