[show abstract][hide abstract] ABSTRACT: The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters \lambda, \mu and \nu are measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system. Comment: Submitted to Physical Review Letters
[show abstract][hide abstract] ABSTRACT: Angular distributions of charged particles produced in Pb-Pb collisions at the CERN SPS have been measured by the NA50 experiment. Measurements have been performed with a silicon microstrip detector at two different beam energies (40 and 158 GeV/nucleon) and over a wide impact parameter (centrality) range. The centrality of the collision has been evaluated both by neutral transverse energy released in the interaction and by spectator nucleons energy (zero degree energy). The charged particle density at midrapidity shows a linear dependence on the number of participating nucleons at both beam energies. The particle density per participant pair and its root s dependence are also studied.
Focus on Multiplicity: International Workshop on Particle Multiplicity in Relativistic Heavy Ion Collisions. 01/2005; 5:86-96.
[show abstract][hide abstract] ABSTRACT: The NA50 experiment at CERN SPS has studied charmonium production in Pb-Pb collisions at 158 GeV/c per nucleon. According to the theoretical predictions the observation of the suppression of the J/psi production yield is expected to be an unambiguous probe for a phase transition from ordinary nuclear matter towards a state in which quarks and gluons are deconfined.
[show abstract][hide abstract] ABSTRACT: We present preliminary results on J/psi production in Pb-Pb collisions at 158 GeV/nucleon, obtained in the analysis of the most recent data sample collected by NA50 experiment in year 2000. The results are compared with an updated absorption curve deduced from new high statistics proton-nucleus data. The measurements reported here confirm the anomalous J/psi suppression already observed by NA50 from previously collected data samples.
Acta Physica Hungarica a-Heavy Ion Physics. 01/2004; 21(2-4):341-347.
[show abstract][hide abstract] ABSTRACT: From proton, deuteron, S- and Pb-induced reactions, experiments NA38 and NA50 have measured muon pair production with various targets. In particular, the production rates of the phi, omega and rho mesons have been simultaneously extracted and compared. Preliminary partial results of the most recent Pb-Pb measurement done in year 2000 by NA50 are presented here. They are also included in the comparison with the results obtained with lighter interacting nuclei.
Journal of Physics G-Nuclear and Particle Physics. 01/2004; 30(1):S277-S282.
[show abstract][hide abstract] ABSTRACT: The NA50 Collaboration has performed a new measurement of the J/psi yield in Pb-Pb collisions at 158 GeV/nucleon in improved experimental conditions. Our preliminary analysis of the year 2000 data sample, while confirming the onset of anomalous suppression and the non saturation of the J/psi/Drell-Yan cross-section ratio, shows that peripheral Pb-Pb interactions follow the normal nuclear absorption pattern, which has in turn been established more precisely thanks to high statistics p-A data.
[show abstract][hide abstract] ABSTRACT: The experiment NA50 studies the strangeness production by means of the BR(mumu)(phi)sigma(phi)/(BR(mumu)(rho)sigma(rho) + BR(mumuomega)sigma(omega)) cross-sections ratio in relativistic heavy ion collisions with respect to proton and light ion collisions. New results for Pb+Pb interactions at 158 A GeV/c are presented (1998 data) and analysed with a different method. The BR(mumu)(phi)sigma(phi)/(BR(mumu)(rho)sigma(rho) + BR(mumu)(omega)sigma(omega)) ratio shows an increase with the number of participants, in agreement with previous results. The inverse slope parameter extracted from the M-T universal scaling is also studied.
Journal of Physics G-Nuclear and Particle Physics. 01/2002; 28(7):1809-1817.
[show abstract][hide abstract] ABSTRACT: The J/psi production in Pb-Pb interactions induced by 158 GeV/c incident Pb ions is studied as a function of centrality, as estimated from the neutral transverse energy or, alternatively, from the very forward hadronic energy of the collision. The J/psi yield exhibits a similar pattern with a first drop for mid-peripheral collisions and a steady decrease for the most central reactions. Conventional hadronic models are unable, to fairly reproduce this trend which finds a natural explanation in a deconfined quark-gluon phase scenario. The J/psi transverse momentum distributions and their dependence with centrality are also reviewed in this presentation.
[show abstract][hide abstract] ABSTRACT: The main goal of the NA50 experiment is to study the J/psi suppression pattern in Pb-Pb interactions, at 158 GeV/c per nucleon at the CERN SPS. We present here the results from the 1996 and 1998 data taking periods. We used new event selection procedures, different analysis techniques and different event centrality estimators and we can now confirm and extend our previous observation that the J/psi is anomalously suppressed when going from peripheral to central Pb-Pb collisions. We observe that in peripheral collisions the J/psi cross section per nucleon-nucleon collision agrees with the pattern inferred from a wide range of measurements with lighter systems, from p-p to S-U. When the collisions become more central a clear departure from this behavior is observed. The 1996 data show a sudden drop in the J/psi production yield for transverse energy values above 40 GeV. The 1998 data provide a big improvement in the study of the most central region, where a second change in the pattern becomes visible. This suppression pattern is confirmed by an independent analysis which uses the zero degree energy (EZDC) as centrality estimator. .
[show abstract][hide abstract] ABSTRACT: The observation of an anomalous J/psi suppression in Pb-Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/psi suppression pattern as a function of the forward hadronic energy E-ZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons N-part and E-ZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/psi suppression as a function of the number of participants. (C) 2001 Elsevier Science B.V. All rights reserved.
[show abstract][hide abstract] ABSTRACT: Strangeness production in relativistic heavy-ion collisions has been studied by experiments NA38 and NA50 (both at the CERN/SPS), through the vectormesons phi and rho + omega. Results from p-W, S-S, S-Cu and S-U at 200 AGeV, and Pb-Pb at 158 AGeV are studied as a function of the dimuon transverse momentum and the collision centrality. A factor of two enhancement of the phi production is observed in sulfur- and lead-induced reactions. A multiplicity study as a function of the number of participants is shown for Pb-Pb interactions. The power-law A dependence of the inclusive cross sections is investigated. Inverse slope parameters are obtained from the d sigma /dM(T) spectra for the phi and the rho + omega vector-mesons.
Journal of Physics G Nuclear and Particle Physics 01/2001; 27(3):405-412. · 5.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: Muon pairs produced in Pb-Pb interactions at 158 GeV/c per nucleon are used to study the transverse momentum distributions of the J/psi, psi' 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. (C) 2001 Published by Elsevier Science B.V.
[show abstract][hide abstract] ABSTRACT: We present the results of experiment NA50 on the production of charmonia states in Pb-Pb collisions at 158 GeV/c per nucleon. For the most peripheral collisions the experimental data agree with ordinary nuclear absorption as deduced from proton and light nuclei induced collisions. For central collisions, we observe an anomalous suppression which significantly departs from normal nuclear absorption and which could result from Debye color screening in a deconfined quark-gluon phase. The dependence of the transverse momentum distributions on the centrality of the Pb-Pb collision is also investigated.
[show abstract][hide abstract] ABSTRACT: The NA50 experiment at CERN SPS studies charmonia and Drell-Yan production in the mu(+)mu(-) decay channel at 158A GeV. The data collected in Pb-Pb collisions during 1995, 1996 and 1998 run periods show that the J/psi is anomalously suppressed in central collisions. This observed suppression pattern can be considered as a strong indication of the production of Quark-Gluon Plasma.
Czechoslovak Journal of Physics. 01/2000; 50:114-119.
[show abstract][hide abstract] ABSTRACT: The J/psi production in 158 A GeV Pb-Pb interactions is studied as a function of centrality. Its pattern, after a first sharp variation around E-T= 40 GeV, continues to fall down and exhibits a curvature change around E-T= 90 GeV. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario.
Intersections of Particle and Nuclear Physics. 01/2000; 549:341-345.
[show abstract][hide abstract] ABSTRACT: The cross section for J/Psi production in Pb-Pb interactions at 158 GeV per nucleon is measured at the CERN SPS by the NA50 experiment. The final results from the 1995 run are presented here together with preliminary ones from the high-statistics 1996 run. An anomalous J/Psi suppression is observed in Pb-Pb collisions as compared to extrapolations of the previous results obtained by the NA38 experiment with proton and lighter ion beams. The results of the two runs are in good agreement. The results from the 1996 run allow the study of the onset of the anomalous suppression within the same set of data, showing evidence of a sharp change of behaviour around a value of neutral transverse energy, as measured by our electromagnetic calorimeter, of about 50 GeV.
[show abstract][hide abstract] ABSTRACT: The threshold effect in the J/psi suppression seen in the NA50 data in lead oil lead interactions at the CERN SPS [1,2] can't be taken into account by conventional models. Other. candidate models  use a phase transition, and therefore let suppose that the thermodynamic variables the defined everywhere that is the so-called thermalization. The in-plane elliptic flow, which has been progosed  in order to probe the thermalization at these beam energies, is found to be actually I,resent ill lead on lead interactions at 158A GcV/c but can't be observed in sulphur on sulphur at 200A GeV/c in the NA38 data [5,6].