134 research outputs found
A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon
We present a new measurement of J/psi production in Pb-Pb collisions at 158
GeV/nucleon, from the data sample collected in year 2000 by the NA50
Collaboration, under improved experimental conditions with respect to previous
years. With the target system placed in vacuum, the setup was better adapted to
study, in particular, the most peripheral nuclear collisions with unprecedented
accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan
cross-sections ratio measured in the most peripheral Pb-Pb interactions is in
good agreement with the nuclear absorption pattern extrapolated from the
studies of proton-nucleus collisions. Furthermore, this new measurement
confirms our previous observation that the (J/psi)/Drell-Yan cross-sections
ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb
collisions and that this ratio persistently decreases up to the most central
collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.
Bottomonium and Drell-Yan production in p-A collisions at 450 GeV
The NA50 Collaboration has measured heavy-quarkonium production in p-A
collisions at 450 GeV incident energy (sqrt(s) = 29.1 GeV). We report here
results on the production of the Upsilon states and of high-mass Drell-Yan muon
pairs (m > 6 GeV). The cross-section at midrapidity and the A-dependence of the
measured yields are determined and compared with the results of other
fixed-target experiments and with the available theoretical estimates. Finally,
we also address some issues concerning the transverse momentum distributions of
the measured dimuons.Comment: 18 pages, 9 figures, to be published in Phys. Lett.
Centrality Behaviour of J/ Production in Na50
The J/ 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
J/psi and psi' production and their normal nuclear absorption in proton-nucleus collisions at 400 GeV
We report a new measurement of J/psi, psi' and Drell-Yan cross-sections, in
the kinematical domain and , performed at the CERN-SPS using 400 GeV/c incident protons on Be, Al,
Cu, Ag, W and Pb targets. The dependence of the charmonia production
cross-sections on the size of the target nucleus allows to quantify the
so-called normal nuclear absorption. In the framework of the Glauber model,
this new measurement is combined with results previously obtained with the same
apparatus, under different experimental conditions, and leads to a precise
determination of the J/psi and psi' absorption cross-sections in the
surrounding nuclear matter.Comment: Accepted for publication in Euro. Phys. J.
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/ suppression is observed, which increases with the centrality of the collisions. The J/ 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 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
The onset of the anomalous J/ suppression in Pb-Pb collisions at the CERN SPS
The 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 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 suppression pattern vs. EZDC is compatible with a sudden suppression mechanism expressed as a function of Npart
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
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