CERN Accelerating science

Two-particle azimuthal correlation functions for different combinations of electric charge of trigger and associate particles: like-sign pairs (open squares), unlike-sign pairs (open triangles) and no constraints (full circles).

\textbf{Top}: Two-particle azimuthal correlation functions of charged hadrons in Pb+Pb collisions at 158$A$~GeV, for centrality bins 0-5~\% (left), 5-10~\% (middle) and 10-20~\% (right). The solid lines illustrate ZYAM-normalised flow contribution to the function, with the dashed ones indicating modulation due to statistical uncertainties on flow coefficients. \textbf{Bottom}: per-trigger conditional yield of associate particles obtained by normalising the flow-subtracted correlation function, again in three centrality bins. All errors are statistical only.

Per-trigger conditional yield for most central ($\sigma/\sigma_{geom} = 0-5~\%$) nucleus-nucleus collisions. Full circles: Pb+Pb at 158$A$~GeV (NA49 preliminary). Open squares: Pb+Au at 158$A$~GeV (CERES preliminary). Open triangles: Au+Au at $\sqrt{s_{NN}}$~=~200~GeV (PHENIX), scaled down to match SPS results around the minimum.