5,095 research outputs found

    Heavy Ion Collisions at the LHC; the ALICE Experiment

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    ALICE (A Large Ion Collider Experiment) is a detector designed to exploit the physics potential of nucleus-nucleus interactions at the LHC. Being a general purpose experiment, it will allow a comprehensive study of hadrons, electrons, muons and photons, produced in the collision of heavy nuclei, up to the highest particle multiplicities anticipated (dNch/dy=8000). In addition to heavy systems (Pb-Pb), we will study collisions at smaller energy densities by using lower-mass ions (e.g. A~40). Reference data will be obtained from pp and p-nucleus collisions. The central part of ALICE covers ‚ą£ő∑‚ą£<0.9|\eta| < 0.9, and consists of an inner tracker (ITS), a TPC and a particle identification array (PID), all embedded in a large magnet with a weak solenoidal field. The experiment is completed by two small area spectrometers in the barrel region (an electromagnetic calorimeter, PHOS, and a high momentum PID detector, HMPID), a forward muon spectrometer (2 degrees to 9.5 degrees) and a ZDC.Comment: 6 pages, 3 figures, LaTeX, uses packages graphicx,epsfig,amsmath,amssymb,cite,xspace,floa

    A Quantitative Analysis of Charmonium Suppression in Nuclear Collisions

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    Data from J/psi and psi' production in p-A collisions are used to determine the cross section for absorption of pre-resonance charmonium in nuclear matter. The J/psi suppression in O-Cu, O-U and S-U collisions is fully reproduced by the corresponding nuclear absorption, while Pb-Pb collisions show an additional suppression increasing with centrality. We study the onset of this change in terms of hadronic comover interactions and conclude that so far no conventional hadronic description can consistently account for all data. Deconfinement, starting at a critical point determined by central S-U collisions, is in accord with the observed suppression pattern.Comment: 37 pages, 12 figures, uses epsfig style, LaTe

    Study of psi' and chi_c decays as feed-down sources of J/psi hadro-production

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    The interpretation of the J/psi suppression patterns observed in nuclear collisions, at CERN and RHIC, as a signature of the formation of a deconfined phase of QCD matter, requires knowing which fractions of the measured J/psi yields, in pp collisions, are due to decays of heavier charmonium states. From a detailed analysis of the available mid-rapidity charmonium hadro-production cross sections, or their ratios, we determine that the J/psi feed-down contributions from psi' and chi_c decays are, respectively, (8.1 +/- 0.3) % and (25 +/- 5) %. These proton-proton values are derived from global averages of the proton-nucleus measurements, assuming that the charmonium states are exponentially absorbed with the length of matter they traverse in the nuclear targets.Comment: 12 pages, 4 figures, 3 table

    Hard probes in nucleus-nucleus collisions

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    The present knowledge on hard processes in the context of heavy ion collisions is reviewed, with particular emphasis on J/psi production. The p-A data on charmonia production from Fermilab experiments is shown to be in excelent agreement with the p-A data collected at CERN. The simultaneous analysis of all existing p-A data reaches a precision which allows us to rule out some preconceived ideas, setting a good frame against which the data collected with ion beams at CERN can be compared.Comment: 15 pages, 8 figures, Latex, uses packages graphicx,rotating,cite, fleqn and the sty file espcrc1_new (included in this submission

    Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies

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    Measurements of open charm hadro-production from CERN and Fermilab experiments are reviewed, with particular emphasis on the absolute cross sections and on their A and sqrt(s) dependences. Differential pt and xf cross sections calculated with the Pythia event generator are found to be in reasonable agreement with recent data. The calculations are scaled to nucleus-nucleus collisions and the expected lepton pair yield is deduced. The charm contribution to the low mass dilepton continuum observed by the CERES experiment is found to be negligible. In particular, it is shown that the observed low mass dilepton excess in S-Au collisions cannot be explained by charm enhancement.Comment: 19 pages, 12 eps figures included. To be published in Z.Phys.

    Avaliação da sustentabilidade dos recursos naturais em área de várzea na região do Paraná de Parintins.

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    As áreas de várzea possuem uma grande diversidade de recursos naturais que são explorados por diversos atores que nela vivem e dependem desse recurso para a sua sobrevivência. Mas poucos estudos nessa área mostram como se encontram a sustentabilidade desses recursos, bem como os impactos gerados pelo seu uso. Este trabalho buscou monitorar os impactos do uso dos recursos naturais em área de manejo de lagos

    Charmonium Suppression by Comover Scattering in Pb+Pb Collisions

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    The first reports of Ōą\psi and Ōą‚Ä≤\psi' production from experiment NA50 at the CERN SPS are compared to predictions based on a hadronic model of charmonium suppression. Data on centrality dependence and total cross sections are in good accord with these predictions.Comment: 9 pages, latex, 6 figures, epsf, figure added and text modified to clarify result

    Unsteady flow past an airfoil pitched at constant rate

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    The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment
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