The production of vector mesons φ, ρ and ω has been measured in Pb–Pb collisions at 158 GeV/c per nucleon incident momentum at the CERN/SPS. The muon spectrometer of experiment NA50 detects φ, ρ and ...ω mesons via their μ+μ− decay channel in the collision center of mass rapidity range 0⩽yCM⩽1. The results reported here show that the relative production of the φ compared to the (ρ+ω) and the φ multiplicity per participant nucleon (Npart) increase with the centrality of the collision. On the other hand, the (ρ+ω) multiplicity per participant does not exhibit any Npart dependence within our errors. The inverse slope parameter as deduced from an exponential fit to the φ transverse mass distribution is 228±10 MeV. Our results are compared with those obtained by experiment NA49 and with theoretical calculations.
The DSI collaboration goal has been the development of large-area silicon drift detectors (SDD) adapted to large-scale production in industry. Such a development is necessary for the use of SDDs in ...large tracking systems, such as the one proposed for the ALICE experiment at LHC (see
Ref. 1). One of the necessary steps towards large-scale production is the study of the doping uniformity in commercially available Si wafers. We have performed a series of measurements aimed at the evaluation of large-scale fluctuations of doping concentration and of the possible influence on the detector quality induced by processing steps. In this paper, we report final results of both resistivity fluctuations and leakage currents measurements.
The
J
/
ψ
azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium ...dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed
J
/
ψ
mesons at SPS energies. Hence, the measurement of
J
/
ψ
elliptic anisotropy, quantified by the Fourier coefficient
v
2
of the
J
/
ψ
azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous
J
/
ψ
suppression observed in Pb-Pb collisions. We present the measured
J
/
ψ
yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient
v
2
as a function of the collision centrality and of the
J
/
ψ
transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or
p
T
sub-samples. The extracted
v
2
values are significantly larger than zero for non-central collisions and are seen to increase with
p
T
.
The observation of an anomalous J/ψ 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/ψ suppression pattern as a function of the forward hadronic energy EZDC 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 Npart and EZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/ψ suppression as a function of the number of participants.
The charged particle multiplicity distribution dNch/dη has been measured by the NA50 experiment in Pb–Pb collisions at the CERN SPS. Measurements were done at incident energies of 40 and 158 GeV per ...nucleon over a broad impact parameter range. The multiplicity distributions are studied as a function of centrality using the number of participating nucleons (Npart), or the number of binary nucleon–nucleon collisions (Ncoll). Their values at midrapidity exhibit a power law scaling behaviour given by Npart1.00 and Ncoll0.75 at 158 GeV. Compatible results are found for the scaling behaviour at 40 GeV. The width of the dNch/dη distributions is larger at 158 than at 40 GeV/nucleon and decreases slightly with centrality at both energies. Our results are compared to similar studies performed by other experiments both at the CERN SPS and at RHIC.
Muon pair production in p-A, S-U and Pb-Pb collisions has been studied by the NA38 and NA50 collaborations at the CERN SPS. In this paper we present an analysis of the dimuon invariant mass region ...between the \(\phi\) and the J/\(\psi\). In p-A collisions we find that, after the subtraction of the combinatorial background due to \(\pi\) and K decays, the superposition of dimuons from semi-leptonic decays of D mesons and from the Drell-Yan process reproduces well the measured mass and transverse momentum spectra. The yield of open charm dimuons required to fit our data leads to a charm production cross section in good agreement with previous measurements. A linear extrapolation of the p-A sources with the product of the mass numbers of the projectile and target nuclei, \(A\times B\), underestimates the dimuon yield measured in S-U and Pb-Pb collisions. The excess increases with the number of participant nucleons, and the ratio between the observed dimuon yield and the expected sources reaches a factor 2 for central Pb-Pb interactions. The kinematical distributions of the measured dimuon excess are compatible with those expected from the open charm contribution.
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