C. Blume

Energy dependence of pion and kaon production in central Pb¿Pb collisions

Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.

Transverse momentum fluctuations in nuclear collisions at 158A GeV

Results are presented on event-by-event fluctuations in transverse momentum of charged particles, produced at forward rapidities in p+p, C+C, Si+Si and Pb+Pb collisions at 158 AGeV. Three different characteristics are discussed: the average transverse momentum of the event, the Phi_pT fluctuation measure and two-particle transverse momentum correlations. In the kinematic region explored, the dynamical fluctuations are found to be small. However, a significant system size dependence of Phi_pT is observed, with the largest value measured in peripheral Pb+Pb interactions. The data are compared with predictions of several models.

Results on correlations and fluctuations from NA49

The large acceptance and high momentum resolution as well as the significant particle identification capabilities of the NA49 experiment at the CERN SPS allow for a broad study of fluctuations and correlations in hadronic interactions. In the first part recent results on event-by-event charge and p_t fluctuations are presented. Charge fluctuations in central Pb+Pb reactions are investigated at three different beam energies (40, 80, and 158 AGeV), while for the p_t fluctuations the focus is put on the system size dependence at 158 AGeV. In the second part recent results on Bose Einstein correlations of h-h- pairs in minimum bias Pb+Pb reactions at 40 and 158 AGeV, as well as of K+K+ and K-K- pairs in central Pb+Pb collisions at 158 AGeV are shown. Additionally, other types of two particle correlations, namely pi p, Lambda p, and Lambda Lambda correlations, have been measured by the NA49 experiment. Finally, results on the energy and system size dependence of deuteron coalescence are discussed.

Bose-Einstein correlations of charged kaons in central Pb + Pb collisions at Ebeam = 158 GeV per nucleon

Abstract Bose–Einstein correlations of charged kaons were measured near mid-rapidity in central Pb+Pb collisions at 158xa0 A xa0GeV by the NA49 experiment at the CERN SPS. Source radii were extracted using the Yano–Koonin–Podgoretsky and Bertsch–Pratt parameterizations. The results are compared to published pion and kaon data. The measured m ⊥ dependence for kaons and pions is consistent with collective transverse expansion of the source and a freeze-out time of aboutxa09.5xa0fm.

Λ and Λ̄ production in central Pb-Pb collisions at 40, 80, and 158A GeV

Production of Lambda and Antilambda hyperons was measured in central Pb-Pb collisions at 40, 80, and 158A GeV beam energy on a fixed target. Transverse mass spectra and rapidity distributions are given for all three energies. The Lambda/pi ratio at midrapidity and in full phase space shows a pronounced maximum between the highest BNL Alternating Gradient Synchrotron and 40A GeV CERN Super Proton Synchrotron energies, whereas the Lambda/pi ratio exhibits a monotonic increase.

Search for deconfinement in A49 at the CERN SPS

Experiment NA49 at the Cern SPS has performed large acceptance measurements of hadron production in pp, pPb, CC, SiSi and PbPb collisions at 40 and 158 A·GeV beam energies. These data allowed a study of particle yields, spectra and correlations as well as event-by-event fluctuations of average event properties of the created hadron system. Results from central PbPb collisions are consistent with the onset of deconfinement during the early stage of the reaction in the lower SPS energy range. A new scaling property of particle production ratios was found which relates collision systems of different size and centrality. Systematics of the evolution of particle production from pp via pPb to PbPb collisions were investigated.