2 00 2 How much is RHIC different from SPS ? Comparison of the p ⊥ - spectra ∗

We show, by means of a simple compilation of the available experimental results, that the p⊥-spectra obtained at RHIC and SPS are strikingly similar up to p⊥ ≃ 1.5− 2 GeV. In fact, the discrepancies between various experimental groups working at the same experiment are of the same size as the differences between RHIC and SPS. Our observation is complementary to the well known fact of the equality of the measured Rside and Rout HBT radii at RHIC and SPS. In essence, it points out that the transverse size of the firecylinder and the strength of the transverse flow are not significantly changed between SPS and RHIC. This suggests that a saturation mechanism is effective already at SPS. We also point out that the dominance of protons over π at large p⊥ can be seen not only in the RHIC data, but already in the SPS data.