89 research outputs found
Transverse momentum distributions of J/, , Drell-Yan and continuum dimuons produced in Pb-Pb interactions at the SPS
Muon pairs produced in Pb-Pb interactions at 158~GeV/ per nucleon are used to study the transverse momentum distributions of the J/, and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb-Pb collision is investigated in detail
Low mass dimuon production in proton and ion induced interactions at SPS
The low mass dimuon spectra collected in -U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The 'excess' events have a harder distribution than the muon pairs from and Dalitz decays, expected to dominate the mass window 0.4—0.65~GeV/. We conjecture that the excess events might be due to annihilations, negligible at low but made visible by the cut applied in the NA38 data. Taking this assumption to parametrise the -U spectra, we proceed with the analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, where we find that the measured mass spectra does not seem to exceed the expected low mass `cocktail' by more than 20%
Evidence for deconfinement of quarks and gluons from the 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 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 suppression we had already observed on a significantly smaller data sample. New event selection and analysis techniques show that, for peripheral collisions, the cross-section per nucleon-nucleon collision agrees with the precise suppression pattern inferred from a wide range of measurements extending from 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 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
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
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