C. Alt

Evidence for an Exotic S = -2, Q = -2 Baryon Resonance in Proton-Proton Collisions at the CERN SPS

Results of resonance searches in the Xi- pi-, Xi- pi+, antiXi+ pi- and antiXi+ pi+ invariant mass spectra in proton-proton collisions at sqrt{s}=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi- pi- baryon resonance with mass of 1.862+/-0.002 GeV/c^2 and width below the detector resolution of about 0.018 GeV/c^2. The significance is estimated to be 4.0 sigma. This state is a candidate for the hypothetical exotic Xi_(3/2)^-- baryon with S = -2, I = 3/2 and a quark content of (d s d s ubar). At the same mass a peak is observed in the Xi- pi+ spectrum which is a candidate for the Xi_(3/2)^0 member of this isospin quartet with a quark content of (d s u s dbar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Energy dependence of particle ratio fluctuations in central Pb+Pb collisions from [v]sNN=6.3 to 17.3 GeV

We present measurements of the energy dependence of event-by-event fluctuations in the K/π and (p+p )/π multiplicity ratios in heavy-ion collisions at the CERN SPS. The particle ratio fluctuations were obtained for central Pb+Pb collisions at five collision energies, √sNN, between 6.3 and 17.3 GeV. After accounting for the effects of finite-number statistics and detector resolution, we extract the strength of nonstatistical fluctuations at each energy. For the K/π ratio, larger fluctuations than expected for independent particle production are found at all collision energies. The fluctuations in the (p+p )/π ratio are smaller than expectations from independent particle production, indicating correlated pion and proton production from resonance decays. For both ratios, the deviation from purely statistical fluctuations shows an increase toward lower collision energies. The results are compared to transport model calculations, which fail to describe the energy dependence of the K/π ratio fluctuations.

Energy dependence of multiplicity fluctuations in heavy ion collisions at 20A to 158A GeV

C. Alt, T. Anticic, B. Baatar,D. Barna, J. Bartke, L. Betev, H. Bia lkowska, C. Blume, B. Boimska, M. Botje, J. Bracinik, R. Bramm, P. Bunčić, V. Cerny, P. Christakoglou, P. Chung, O. Chvala, J.G. Cramer, P. Csató, P. Dinkelaker, V. Eckardt, D. Flierl, Z. Fodor, P. Foka, V. Friese, J. Gál, M. Gaździcki, V. Genchev, G. Georgopoulos, E. G ladysz, K. Grebieszkow, S. Hegyi, C. Höhne, K. Kadija, A. Karev, D. Kikola, M. Kliemant, S. Kniege, V.I. Kolesnikov, E. Kornas, R. Korus, M. Kowalski, I. Kraus, M. Kreps, A. Laszlo, R. Lacey, M. van Leeuwen, P. Lévai, L. Litov, B. Lungwitz, M. Makariev, A.I. Malakhov, M. Mateev, G.L. Melkumov, A. Mischke, M. Mitrovski, J. Molnár, St. Mrówczyński, V. Nicolic, G. Pálla, A.D. Panagiotou, D. Panayotov, A. Petridis, W. Peryt, M. Pikna, J. Pluta, D. Prindle, F. Pühlhofer, R. Renfordt, C. Roland, G. Roland, M. Rybczyński, A. Rybicki, A. Sandoval, N. Schmitz, T. Schuster, P. Seyboth, F. Siklér, B. Sitar, E. Skrzypczak, M. Slodkowski, G. Stefanek, R. Stock, C. Strabel, H. Ströbele, T. Susa, I. Szentpétery, J. Sziklai, M. Szuba, P. Szymanski, V. Trubnikov, M. Utvic, D. Varga, M. Vassiliou, G.I. Veres, G. Vesztergombi, D. Vranić, A. Wetzler, Z. W lodarczyk, A. Wojtaszek, I.K. Yoo, J. Zimányi

Bose-Einstein correlations of pi-pi- pairs in central Pb+Pb collisions at A-20, A-30, A-40, A-80, and A-158 GeV

C. Alt, T. Anticic, B. Baatar, D. Barna, J. Bartke, L. Betev, H. Bia lkowska, C. Blume, B. Boimska, M. Botje, J. Bracinik, R. Bramm, P. Bunčić, V. Cerny, P. Christakoglou, P. Chung, O. Chvala, J.G. Cramer, P. Csató, P. Dinkelaker, V. Eckardt, D. Flierl, Z. Fodor, P. Foka, V. Friese, J. Gál, M. Gaździcki, V. Genchev, G. Georgopoulos, E. G ladysz, K. Grebieszkow, S. Hegyi, C. Höhne, K. Kadija, A. Karev, D. Kikola, M. Kliemant, S. Kniege, V.I. Kolesnikov, E. Kornas, R. Korus, M. Kowalski, I. Kraus, M. Kreps, A. Laszlo, R. Lacey, M. van Leeuwen, P. Lévai, L. Litov, B. Lungwitz, M. Makariev, A.I. Malakhov, M. Mateev, G.L. Melkumov, A. Mischke, M. Mitrovski, J. Molnár, St. Mrówczyński, V. Nicolic, G. Pálla, A.D. Panagiotou, D. Panayotov, A. Petridis, W. Peryt, M. Pikna, J. Pluta, D. Prindle, F. Pühlhofer, R. Renfordt, C. Roland, G. Roland, M. Rybczyński, A. Rybicki, A. Sandoval, N. Schmitz, T. Schuster, P. Seyboth, F. Siklér, B. Sitar, E. Skrzypczak, M. Slodkowski, G. Stefanek, R. Stock, C. Strabel, H. Ströbele, T. Susa, I. Szentpétery, J. Sziklai, M. Szuba2, P. Szymanski, V. Trubnikov, D. Varga, M. Vassiliou, G.I. Veres, G. Vesztergombi, D. Vranić, A. Wetzler, Z. W lodarczyk, A. Wojtaszek, I.K. Yoo, and J. Zimányi NIKHEF, Amsterdam, Netherlands Department of Physics, University of Athens, Athens, Greece Comenius University, Bratislava, Slovakia KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary MIT, Cambridge, USA Institute of Nuclear Physics, Cracow, Poland Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany Joint Institute for Nuclear Research, Dubna, Russia Fachbereich Physik der Universität, Frankfurt, Germany CERN, Geneva, Switzerland Institute of Physics Świȩtokrzyska Academy, Kielce, Poland Fachbereich Physik der Universität, Marburg, Germany Max-Planck-Institut für Physik, Munich, Germany Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic Department of Physics, Pusan National University, Pusan, Republic of Korea Nuclear Physics Laboratory, University of Washington, Seattle, WA, USA Atomic Physics Department, Sofia University St Kliment Ohridski, Sofia, Bulgaria Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria Department of Chemistry, Stony Brook Univ (SUNYSB), Stony Brook, USA Institute for Nuclear Studies, Warsaw, Poland Institute for Experimental Physics, University of Warsaw, Warsaw, Poland Faculty of Physics, Warsaw University of Technology, Warsaw, Poland and Rudjer Boskovic Institute, Zagreb, Croatia

Three-dimensional two-pion source image from Pb+Pb collisions at √ sNN=17.3 GeV: new constraints for source breakup dynamics

Abstract Source imaging methodology is used to provide a three-dimensional two-pion source function for mid-rapidity pion pairs with p T 70 MeV / c in central (0–7%) Pb + Pb collisions at s NN = 17.3 GeV . Prominent non-Gaussian tails are observed in the pion pair transverse momentum (outward) and in the beam (longitudinal) directions. Model calculations reproduce them with the assumption of Bjorken longitudinal boost invariance and transverse flow blast-wave dynamics; they also yield a proper time for breakup and emission duration for the pion source.

Elliptic flow of Λ hyperons in Pb+Pb collisions at 158A GeV

The elliptic flow of Lambda hyperons has been measured by the NA49 collaboration at the CERN-SPS in semi-central Pb+Pb collisions at 158A GeV. The standard method of correlating particles with the event plane was used. Measurements of v2 near mid-rapidity are reported as a function of rapidity, centrality and transverse momentum. Elliptic flow of Lambda particles increases both with the impact parameter and with the transverse momentum. It is compared with v2 for pions and protons as well as with model calculations. The observation of significant elliptic flow and its mass dependence suggest strong collective behaviour of the matter produced in collisions of heavy nuclei already at the SPS. Scaling properties of elliptic flow of different particle species have been tested at 158A GeV. The limited pT range of the data does not allow for a decisive test of the coalescence model.

Strangeness from 20 A GeV to 158 A GeV

New results from the energy scan programme of NA49, in particular kaon production at 30 A GeV and Φ production at 40 and 80 A GeV are presented. The K + /π + ratio shows a pronounced maximum at 30 A GeV; the kaon slope parameters are constant at SPS energies. Both findings support the scenario of a phase transition at about 30 A GeV beam energy. The Φ/π ratio increases smoothly with beam energy, showing an energy dependence similar to K - /π - . The measured particle yields can be reproduced by a hadron gas model, with chemical freeze-out parameters on a smooth curve in the T-μ B plane. The transverse spectra can be understood as resulting from a rapidly expanding, locally equilibrated source. No evidence for an earlier kinetic decoupling of heavy hyperons is found.

Upper limit of D0production in central Pb-Pb collisions at 158AGeV

Results are presented from a search for the decays D0→K-π+ and D 0→K+π- in a sample of 3.8×106 central Pb-Pb events collected with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed. An upper limit on D0 production is derived and compared to predictions from several models.

Ω- and Ω̄+ production in central Pb+Pb collisions at 40 and 158AGeV

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models.

Strangeness from 20-A-GeV to 158-A-GeV

New results from the energy scan programme of NA49, in particular kaon production at 30 A GeV and Φ production at 40 and 80 A GeV are presented. The K + /π + ratio shows a pronounced maximum at 30 A GeV; the kaon slope parameters are constant at SPS energies. Both findings support the scenario of a phase transition at about 30 A GeV beam energy. The Φ/π ratio increases smoothly with beam energy, showing an energy dependence similar to K - /π - . The measured particle yields can be reproduced by a hadron gas model, with chemical freeze-out parameters on a smooth curve in the T-μ B plane. The transverse spectra can be understood as resulting from a rapidly expanding, locally equilibrated source. No evidence for an earlier kinetic decoupling of heavy hyperons is found.