Two particle azimuthal correlations at high transverse momentum in Pb - Au at 158 AGeV/c

The analysis of two-particle azimuthal angular correlations at high transverse momentum from Pb+Au collisions at 158 AGeV/c at SPS reveals substantial modifications of the away-side peak as compared to the distributions from p+p reactions. The data recorded with the CERES Time-Projection Chamber, which provides excellent tracking efficiency, suggest that the observed modification of the back-to-back structure implies significant re-interactions of the scattered partons within the medium. These findings at top SPS energy show features qualitatively similar to the results obtained at RHIC from Au+Au collisions at s = 200 GeV / c and Cu+Cu collisions at s = 62 GeV / c [S.S. Adler et al., PHENIX Collaboration, arXiv:nucl-ex/0507004 , M. McCumber and J. Frantz, arXiv:nucl-ex/0511048 ]. We present the centrality and charge dependent conditional di-jet yields for similar transverse momentum windows as investigated by the RHIC experiments [S.S. Adler et al., PHENIX Collaboration, arXiv:nucl-ex/0507004 , M. McCumber and J. Frantz, arXiv:nucl-ex/0511048 , J. Adams et al., STAR Collaboration, Phys. Rev. Lett. 95 (2005) 152301, arXiv:nucl-ex/0501016 ].