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The NA60 experiment studies open charm and prompt dimuon production in proton-nucleus and nucleus-nucleus collisions at the CERN SPS. During 2003 the experiment collected data in Indium-Indium collisions at 158 GeV per nucleon. In this paper the first results on low mass dimuons, intermediate mass dimuons and J/ψ suppression are presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The quality of the dimuon measurements made by NA60, in proton-nucleus and heavy-ion collisions, is much better than that reached by previous experiments, such as NA38 and NA50. The most important improvement is due to the use of a radiation-tolerant silicon vertex telescope, placed immediately downstream of the target. This allows NA60 to do a high quality measurement of [lowercase_phi_synonym] meson yields and pT distributions. This paper presents results obtained in p-Be, p-In and p-Pb collisions at 400 GeV, from data collected in 2002, and in In-In collisions at 158 AGeV, as a function of centrality, from the 2003 running period. In particular, we show that the inverse mT slope measured in In-In collisions, in the [lowercase_phi_synonym] → μμ decay channel, increases with the number of nucleons participating in the collisions, rather than following a flat trend as seen in the NA50 data collected in the same decay channel but restricted to high pT values. We also show that our measurements seem to agree with the values previously measured by NA49, using [lowercase_phi_synonym] → KK decays, in Pb-Pb and other collision systems. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The NA60 experiment collected data on dimuon production in indium-indium collisions at 158 GeV/c per incident nucleon, in year 2003, to contribute to the clarification of several questions raised by previous experiments studying high-energy heavy-ion physics at the CERN SPS in search of the quark gluon plasma. Among these previous results stands the observation, by NA50, that the production yield of J/ψ mesons is suppressed in central Pb-Pb collisions beyond the normal nuclear absorption defined by proton-nucleus data. By comparing the centrality dependence of the suppression pattern between different colliding systems, S-U, Pb-Pb and In-In, we should be able to identify the corresponding scaling variable, and the physics mechanism driving the suppression. In this paper, we will present the ratio of J/ψ and Drell-Yan production cross-sections in indium-indium collisions, in three centrality bins, and how these values compare to previous measurements. We will also present a study of the transverse momentum distributions of the J/ψ mesons, in seven centrality bins. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The NA60 experiment takes place at the SPS at CERN, to study the production of open charm and prompt dimuons in collisions induced by proton and heavy ion beams on nuclear targets. For this task, several novel detector systems were added to the dimuon spectrometer and zero-degree calorimeter, which were previously used in the NA50 experiment. The main upgrade is a new silicon pixel vertex spectrometer. It tracks the charged particles that are produced through the collisions in the target and allows us to match their trajectories and momenta with those of the muons that are measured behind the hadron absorber in the muon spectrometer. Besides improving considerably the dimuon mass resolution, the vertex telescope measures the offset of each muon track with respect to the interaction point. This allows us to select events where charm mesons were produced. We present in this article first results from dimuon data that were acquired in Summer 2002 with a 400 GeV proton beam. A silicon microstrip telescope was used at that time, since only a part of the pixel telescope was completed. The results include an improved dimuon mass resolution and an extended phase space coverage when compared with previous experiments. Data from Pb-Pb collisions at 20 and 30 GeV per nucleon were collected in October 2002 with three planes of pixel detectors. We show the very good accuracy with which we could reconstruct the interaction vertex. We conclude with a reminder of our physics programme and the ongoing completion of the pixel detector telescope for the Indium-Indium run at 158 GeV per nucleon, scheduled for September and October 2003. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The main goal of the NA50 experiment is to study the J/ψ 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/ψ is anomalously suppressed when going from peripheral to central Pb-Pb collisions. We observe that in peripheral collisions the J/ψ 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/ψ 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 (E[sub ZDC]) as centrality estimator. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract. The J/ψ production in 158 A GeV Pb-Pb interactions is studied as a function of centrality. Its pattern, after a first sharp variation around E[sub T]= 40 GeV, continues to fall down and exhibits a curvature change around E[sub T]= 90 GeV. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario. [ABSTRACT FROM AUTHOR]