New results of the NA49 Collaboration on strange particle production are presented. Rapidity and transverse mass spectra as well as total multiplicities are discussed. The study of their evolution from AGS over SPS to the highest RHIC energy reveals a couple of interesting features. These include a sudden change in the energy dependence of the mt-spectra and of the yields of strange hadrons around 30 A GeV. Both are found to be difficult to be reproduced in a hadronic scenario, but might be an indication for a phase transition to a quark–gluon plasma.

Abstract.The NA60 experiment studies dimuon production in In-In and p-A collisions at the CERN SPS. We report recent results on J/ψ production, measured through its muon pair decay. As a function of centrality, we show that in In-In the J/ψ yield is suppressed beyond expectations from nuclear absorption. We present also for the first time results on J/ψ production in p-A collisions at 158 GeV, the same energy of the nucleus-nucleus data. For both p-A and In-In we show preliminary results on ψ ′ suppression. Finally, we have studied the kinematical distributions of the J/ψ produced in In-In collisions. We present results on transverse momentum and rapidity, as well as on the angular distribution of the J/ψ decay products. Introduction and data analysisThe production of the charmonium states in ultrarelativistic heavy-ion collisions has been recognized as a key observable for the occurrence of deconfinement since the very beginning of the studies in this field [1]. A suppression of the charmonium yield beyond expectations from a pure nuclear absorption scenario has been observed both at SPS and RHIC energies by the NA38/NA50 [2] and PHENIX [3] experiments, respectively. However, the interpretation of the experimental observations is still under debate, with explanations including, among others, the production of a fully thermalized QGP [4], of a percolating partonic condensate [5], or of a very dense hadron gas [6,7]. Therefore, accurate experimental investigations, carried out with several projectile-target systems, are mandatory in order to confirm or exclude the various proposed scenarios. Clearly, in order to claim a suppression signal beyond nuclear absorption, accurate p-A reference data, taken in the same energy/kinematical conditions as those for the nucleus-nucleus data, are also necessary. In parallel to these studies, the investigation of the kinematical distributions of charmonia provides interesting and complementary insights to the physics picture, giving information on production mechanisms and initial state effects.All of these aspects of charmonia production are presently being studied, at the SPS, by the NA60 experiment. The apparatus consists of a muon spectrometer, inherited from NA50, which is also used for triggering on the production of a muon pair. A vertex ‡ For the full list of NA60 authors and acknowledgements, see Appendix 'Collaborations' of this volume

A review of recent NA57 results on K0S and hyperon production from Pb–Pb collisions at 40 and 158 A GeV/c is presented. An energy and centrality dependence of particle yields, strangeness enhancements as well as transverse mass spectra at mid-rapidity are discussed.

Recent results of the NA49 energy scan programme show a sharp maximum of the ratio of K + to π + yields in central Pb+Pb collisions at beam energies of 20-30 A GeV. This observation has been interpreted as an indication of a phase transition at low SPS energies. We present results on event-by-event fluctuations of the kaon to pion and proton to pion ratios at beam energies close to this maximum. A significant increase of the fluctuation signal of the kaon to pion ratio with deceasing beam energy is observed.