Centrality Behaviour of J/ψ\psi Production in Na50

The J/$\psi$ production in 158 A GeV Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured with the electromagnetic or with the very forward calorimeters. After a first sharp variation at mid centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario. We report also preliminary results on the measured charged multiplicity, as given by a dedicated detector.Comment: 5 pages, 7 figures (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

The onset of the anomalous J/ψ\psi suppression in Pb-Pb collisions at the CERN SPS

The $J/\psi$ suppression observed by the NA50 experiment is one of the most striking signatures for quark gluon plasma formation in Pb-Pb collisions at 158 AGeV. The $J/\psi$ production has been studied as a function of the centrality of the collision estimated via the forward energy EZDC released in a zero degree calorimeter (ZDC). The study of the correlation between the number of participant nucleons in the collisions, Npart, and EZDC allows to check whether the $J/\psi$ suppression pattern vs. EZDC is compatible with a sudden $J/\psi$ suppression mechanism expressed as a function of Npart

NA50 final results on charmonia suppression

NA50The last results from the NA50 experiment on charmonia production in Pb-Pb interactions at 158 GeV/c per nucleon are presented. A strong J/$\psi$ suppression is observed, which increases with the centrality of the collisions. The J/$\psi$ production is seen to be anomalously suppressed starting at mid-centralities, when compared to a reference taken from proton-induced collisions. The most recent developments on the determination of this normal absorption curve are explained. It is also shown that for sulphur-induced reactions there is full agreement with the extrapolated normal p-A behaviour. The suppression of $\psi'$ production in heavy ion collisions (Pb-Pb and S-U) is also presented. It is seen to increase with the centrality of the collisions, and to be significantly stronger than the one measured in proton-induced reactions

Results on open charm from NA50

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Evidence for deconfinement of quarks and gluons from the J/psiJ/psi suppression pattern measured in Pb-Pb collisions at the CERN-SPS

NA50The analysis of the data collected by the NA50 experiment in 1998, reported in this paper, extends and clarifies the pattern of thepreviously observed \jpsi\ anomalous suppression. This newmeasurement, besides providing a deeper understanding of the previousobservations, reveals a steady significative decrease in the \jpsi\ production rate up to the most central Pb-Pb collisions. It clearlyrules out the presently available conventional (hadronic) models of\jpsi\ suppression, which unanimously predict a saturation of the\jpsi\ rate for central Pb-Pb collisions. On the contrary andtogether with the sharp onset of the anomalous suppression previouslyreported, the new observation leads to a global production ratepattern which finds its natural explanation in the framework of theformation of a deconfined state of quarks and gluons

Observation of a threshold effect in the anomalous J/ψJ/\psi suppression

We report on a search for a phase transition from ordinary nuclear matter to a state of deconfined quarks and gluons as predicted by lattice QCD calculations. A new measurement of charmonium production in Pb-Pb interactions at 158 GeV/c per nucleon agrees with our previous results and confirms the anomalous $J/\psi$ suppression we had already observed on a significantly smaller data sample. New event selection and analysis techniques show that, for peripheral collisions, the $J/\psi$ cross-section per nucleon-nucleon collision agrees with the precise suppression pattern inferred from a wide range of measurements extending from $p-p$ up to S-U collisions. As the collisions become more central, the Pb-Pb cross-section exhibits a clear departure from this normal behaviour. The onset of the anomalous $J/\psi$ suppression reported here is the first clear observation of a threshold effect in heavy ion collisions and can be considered as a strong indication of the production of a deconfined quark-gluon phase in central Pb-Pb collisions

Strangeness measurements in NA50 experiment with Pb projectiles

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Charmonium production in Pb-Pb collisions

NA50The elaboration of specific media-planning is necessary to communicate with an opinion leader. Opinion leaders in 27 product categories are selected from a 10,000 sample of French representative consumers. Magazine is the favorite media of opinion leaders; the more important is the number of product categories in which a consumer is leaders, the greater the media consumption. Leaders do not systematically prefer the Internet, their preference appears to be category specific. However, a second study conducted among 600 brand website visitors shows that brand sites represent a major information source for the leaders

Light-induced modulated structures, intrinsic optical multistability and instabilities for the competitive wave interactions in liquid crystals

The multistability and temporal instabilities of nonlinear wave process with an energy transfer and competition between different light polarization components have been studied both theoretically and experimentally for a nonhomogeneous anisotropic medium with threshold nonlinearity. A feedback for such wave interactions, when the laser radiation induces the bulk-gratings of refractive index, arises because of the non-local response of the anisotropic elastic medium on the external field.On étudie à la fois théoriquement et expérimentalement la multistabilité et les instabilités temporelles de processus ondulatoires non linéaires dans les conditions de transfert d'énergie et de compétition entre les différentes composantes de polarisation, pour un milieu anisotrope inhomogène présentant une non-linéarité à seuil. Dans de telles interactions, il se produit un couplage rétroactif lorsque le rayonnement laser induit un réseau d'indice de réfraction dans le milieu, à cause de la réponse non locale du milieu élastique anisotrope au champ extérieur