Semihard scattering unraveled from collective flow at the SPS

A study of elliptic flow and two-particle azimuthal correlations of charged particles (\(0.5 < p_{{\text{T}}} < 2.5\) GeV/c) and high-\(p_{\rm T}\) pions (\(1.2 < p_{{\text{T}}} < 3.5\) GeV/c) in Pb + Au collisions at 158A GeV/c, close to midrapidity, is presented. Elliptic flow (v2) rises linearly with \(p_{\rm T}\) to a value of about 10\(\%\) at 2 GeV/c. Beyond \(p_{\rm T}\approx\) 1.5 GeV/c, the slope decreases and possibly indicates a v2 saturation at high \(p_{\rm T}\). Two-pion azimuthal anisotropies for \(p_{\rm T} > \) 1.2 GeV/c exceed the v2 values by about 60\(\%\) in semicentral collisions. This non-flow component is attributed to near-side and away-side jetlike correlations. While the near-side peak remains constant with centrality 0.23\(\pm\)0.03 rad, as expected for fragmentation, the away-side peak experiences broadening and disappears in central collisions.