L. Dietrich

Enhanced Production of Low-Mass Electron-Positron Pairs in 40-AGeV Pb-Au Collisions at the CERN SPS

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2<m</=1 GeV/c(2) is enhanced over the expectation from neutral meson decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c Pb-Au collisions

Measurements of event-by-event fluctuations of the mean transverse momentum in Pb-Au collisions at 40, 80, and 158 A GeV/c are presented. A significant excess of mean p_T fluctuations at mid-rapidity is observed over the expectation from statistically independent particle emission. The results are somewhat smaller than recent measurements at RHIC. A possible non-monotonic behaviour of the mean p_T fluctuations as function of collision energy, which may have indicated that the system has passed the critical point of the QCD phase diagram in the range of mu_B under investigation, has not been observed. The centrality dependence of mean p_T fluctuations in Pb-Au is consistent with an extrapolation from pp collisions assuming that the non-statistical fluctuations scale with multiplicity. The results are compared to calculations by the RQMD and UrQMD event generators.

Leptonic and charged kaon decay modes of the phi meson measured in heavy-ion collisions at the CERN super proton synchrotron.

We report on results of a measurement of meson production in central Pb-Au collisions at E(lab) = 158A GeV. For the first time in the history of high energy heavy-ion collisions, phi mesons were reconstructed both in the K+K- and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05 +/- 0.14(stat) +/- 0.25(syst) and 2.04 +/- 0.49(stat) +/- 0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the phi yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.

Latest results from CERES/NA45

D. Adamová, G. Agakichiev, H. Appelshäuser, V. Belaga, P. Braun-Munzinger, R. Campagnolo, A. Castillo, A. Cherlin, S. Damjanović, T. Dietel, L. Dietrich, A. Drees , S. I. Esumi, K. Filimonov, K. Fomenko, Z. Fraenkel, C. Garabatos, P. Glässel, G. Hering, J. Holeczek, V. Kushpil, B. Lenkeit, W. Ludolphs, A. Maas, A. Maŕın, F. Messer , J. Milošević, A. Milov, D. Mískowiec, L. Musa, Yu. Panebrattsev, O. Petchenova, V. Petráček, A. Pfeiffer, J. Rak, I. Ravinovich, P. Rehak, M. Richter, H. Sako, W. Schmitz, J. Schukraft, S. Sedykh, W. Seipp, A. Sharma, S. Shimansky, J. Sĺıvová, H. J. Specht, J. Stachel, M. Šumbera, H. Tilsner, I. Tserruya, J. P. Wessels, T. Wienold, B. Windelband, J. P. Wurm, W. Xie, S. Yurevich, V. Yurevich

The CERES/NA45 radial drift Time Projection Chamber

The design, calibration, and performance of the first radial drift Time Projection Chamber (TPC) are presented. The TPC was built and installed at the CERES/NA45 experiment at the CERN SPS in the late nineties, with the objective to improve the momentum resolution of the spectrometer. The upgraded experiment took data twice, in 1999 and in 2000. After a detailed study of residual distortions a spatial resolution of 340μm in the azimuthal and 640μm in the radial direction was achieved, corresponding to a momentum resolution of ∆p/p = √ (1% · p/GeV) + (2%).

Flow and non-flow event anisotropies at the SPS

Abstract A study of differential elliptic event anisotropies ( ν 2 ) of charge particles and high- p T pions in 158 AGeV/c Pb+Au collisions is presented. Results from correlations with respect to the event plane and from two-particle azimuthal correlations are compared. The latter give systematically higher ν 2 values at p T >1.2 GeV/c providing possibly an evidence of a non-flow semihard component.

Lambda production in 40 A GeV/c Pb–Au collisions

During the 1999 lead run, CERES has measured hadron and electron-pair production at 40 A GeV/c beam momentum with the spectrometer upgraded by the addition of a radial TPC. Here the analysis of Λ and will be presented.