K+ versus Λ flow in relativistic heavy-ion collisions

We study K+ and Lambda flow in heavy-ion collisions at beam energies of about 2 A GeV. We present our results in both the "traditional" (i.e., in terms of the average transverse momentum in the reaction plane) as well as "modern" (i.e., in terms of coefficients of the Fourier analysis of azimuthal distributions) methods of flow analysis. We find significant differences between the K+ and the Lambda flow: while the Lambda flow is basically similar to that of nucleons, the K+ flow almost disappears. This difference is attributed chiefly to their different mean field potentials in dense matter. The comparisons with the experimental data, as well as theoretical results from independent calculations, indicate clearly the pivotal roles of both K+ and Lambda medium effects. We emphasize that similar experimental data from independent collaborations are essential for the eventual verification of these medium effects. (C) 1998 Published by Elsevier Science B.V.