181 research outputs found

    Lambda and Antilambda reconstruction in central Pb C Pb collisions using

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    The large acceptance time projection chambers of the NA49 experiment are used to record the trajectory of charged particles from Pb + Pb collisions at 158 GeV per nucleon. Neutral strange hadrons have been reconstructed from their charged decay products. To obtain distributions of Λ, and Ks0 in discrete bins of rapidity, y, and transverse momentum, pT, calculations have been performed to determine the acceptance of the detector and the efficiency of the reconstruction software as a function of both variables. The lifetime distributions obtained give values of cτ = 7.8 ± 0.6 cm for Λ and cτ = 2.5 ± 0.3 cm for Ks0, consistent with data book values

    Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

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    We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement

    Strange Particle Production in p+p, p+Pb and Pb+Pb Interactions from NA49

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    Recent NA49 results on Lambda, Antilambda, Xi- and Antixi+ production in minimum bias p+p and centrality selected p+Pb collisions at 158 GeV/c, and the results on Lambda, Antilambda, K+ and K- production in central Pb+Pb collisions at 40, 80 and 158 A GeV are discussed and compared with other available data. By comparing the energy dependence of Lambda and Antilambda production at mid-rapidity a striking similarity is observed between p+p and A+A data. This is also seen in the energy dependence of the Lambda/pi ratio. K+/pi at mid-rapidity is affected in a similar way, due to the associated production of K+ together with Lambda particles. The observed yields increase faster than the number of wounded nucleons when comparing p+Pb to p+p. As already observed in A+A collisions, the increase is larger for multistrange than for strange baryons and for baryons than for anti-baryons.Comment: 8 pages, 10 figures, To appear in proceedings of Strange Quark in Matter 2001-A Flavourspace Odyssey, Frankfurt am Main, Germany, 24-29. Sept. 200

    Baryon Number Transfer in Hadron+Nucleus and Nucleus+Nucleus Collisions: A Link between Elementary and Complex Interactions

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    The baryon number transfer is studied in elementary and complex hadronic interactions at the CERN experiment NA49 at the SPS, at 158 AGeV beam energy (\sqrt{s}=17.2 GeV). A two component picture is proposed, which builds up the net proton distribution from a target and a projectile component. Using pion beam, the projectile component is experimentally determined for p+p and p+A interactions. A similar stopping behaviour of the projectile component is found for p+A and A+A interactions. Based on these observations, the baryon transfer is assumed to provide a common scale of inelasticity in p+p, p+A and A+A interactions. A model-independent way is proposed to predict the pion multiplicity in A+A.Comment: 10 pages, 12 figures. To appear in the proceedings of International Workshop on Quark and Hadron Dynamics in Relativistic Heavy Ion Collisions (BP 2002), Budapest, Hungary, 3-7 Mar 200

    Directed and Elliptic Flow in 158 GeV/Nucleon Pb + Pb Collisions. Draft 2.2.

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    The directed and elliptic flow of protons and charged pions has been observed from the semi-central collisions of a 158 GeV/nucleon Pb beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low pt. The elliptic flow of both is fairly independent of rapidity but rises with pt. PACS numbers: 25.75.-q, 25.75.L

    Xi and Xi-bar production in 158 GeV/nucleon Pb + Pb collisions

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    We report measurements of Xi and Xi-bar hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy = 2.29 +/- 0.12 for Xi, and 0.52 +/- 0.05 for Xi-bar, leading to the ratio of Xi-bar/Xi = 0.23 +/- 0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of 300 MeV near mid-rapidity. The estimated total yield of Xi particles in Pb+Pb central interactions amounts to 7.4 +/- 1.0 per collision. Comparison to Xi production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Xi production in Pb+Pb central collisions over elementary hadron interactions

    Energy dependence of hadronic observables in central Pb+Pb reactions at the CERN SPS

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    In the recent years the NA49 experiment has collected data on Pb+Pb collisions at beam energies between 20 to 158 AGeV with the objective to cover the critical region of energy densities where the expected phase transition to a deconfined phase might occur in the early stage of the reactions. In this contribution the energy dependence of various hadronic observables is presented. These include m_t- and rapidity- distributions, particle ratio fluctuations, as well as HBT radii.Comment: 7 pages, 5 figures, Proceedings of the 20th Winter Workshop on Nuclear Dynamics, Jamaic

    Upper limit of D 0 production in central Pb-Pb collisions at 158 A GeV

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    Results are presented from a search for the decays D0 -> K min pi plus and D0 bar -> K plus pi min in a sample of 3.8x10^6 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

    System size dependence of strangeness production at 158 AGeV

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    Strange particle production in A+A interactions at 158 AGeV is studied by the CERN experiment NA49 as a function of system size and collision geometry. Yields of charged kaons, phi and Lambda are measured and compared to those of pions in central C+C, Si+Si and centrality-selected Pb+Pb reactions. An overall increase of relative strangeness production with the size of the system is observed which does not scale with the number of participants. Arguing that rescattering of secondaries plays a minor role in small systems the observed strangeness enhancement can be related to the space-time density of the primary nucleon-nucleon collisions
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