psi' production is studied in Pb-Pb collisions at 158 GeV/c per nucleon incident momentum. Absolute cross-sections are measured and production rates are investigated as a function of the centrality of the collision. The results are compared with those obtained for lighter colliding systems and also for the J/psi meson produced under identical conditions.
We report a new measurement of J/psi, psi' and Drell-Yan cross-sections, in the kinematical domain $-0.425<y_{\rm cm}<0.575$ and $-0.5<\cos\theta_{\rm CS}<0.5$, 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.
Cross sections for J ψ,ψ′ and Drell-Yan production in Pb+Pb collisions at 158×A GeV/c are presented and compared with results obtained by the NA38 and NA51 collaborations. The Pb+Pb data have been collected by the NA50 collaboration using the NA38 dimuon spectrometer. The Drell-Yan mechanism is found to scale as (A projectile · B target ) in p+B target and A projectile + B target collisions including Pb+Pb collisions. Regarding J ψ , an anomalous suppression is observed in Pb+Pb collisions with respect to the suppression observed in p+B target , O+B target and S+U collisions. The cross section ratios ψ′ ( J ψ ) are similar in Pb+Pb and S+U collisions.
Charmonium production in p – A collisions is a unique tool for the study of the interaction of bound c c states in nuclear matter. It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell–Yan production in proton–nucleus collisions at 450 GeV/ c . The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section σ abs pA for J / ψ and ψ ′. Then, we compare the J / ψ absorption in proton–nucleus and sulphur–uranium interactions, using NA38 data. We obtain that, for the J / ψ , σ abs pA and σ abs SU are compatible, showing that no sizeable additional suppression mechanism is present in S–U collisions, and confirming that the anomalous J / ψ suppression only sets in for Pb–Pb interactions.
The cross section for K + meson production in collisions of 36 Ar ions on a 48 Ti target has been measured at an incident energy of 92 MeV per nucleon. A description of the experimental set-up is given. Twelve events attributed to monoenergetic muons following the decay of stopped kaons have been identified. From these events, one infers a production cross section of 240 pb. Data are briefly discussed.
The production of eta mesons has been measured in the proton-proton interaction close to the reaction threshold using the COSY-11 internal facility at the cooler synchrotron COSY. Total cross sections were determined for eight different excess energies in the range from 0.5 MeV to 5.4 MeV. The energy dependence of the total cross section is well described by the available phase-space volume weighted by FSI factors for the proton-proton and proton-eta pairs.
Results from the HELIOS External Spectrometer on kaon production in 200 GeV/ A S + W and p + W collisions are presented. The K π ratios are compared with results from a lower beam energy and are found to be remarkably similar. Evidence for secondary production of K + by meson-baryon rescattering is reviewed. Our results at y = 1.0–1.5 are compared with neutral strange particle results at midrapidity.
A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration of Lambda directed flow. The transverse mass spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence of Lambda multiplicity on impact parameter is observed, from which a total Lambda + Sigma^0 production cross section of $112 +/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.
We report on a sample of Jψ mesons coming from secondary vertices, a characteristic of heavyquark decay, detected in the Fermilab Meson West spectrometer. Based on eight signal events in which a Jψ emerges from a secondary vertex occurring in an air-gap region, we obtain an inclusive bb¯ cross section of 75 ± 31 ± 26 nb/nucleon. This result is compared to recent QCD predictions. We have also observed several events in the exclusive decay modes B±→Jψ+K± and B0→Jψ+K0* in which the B mass is fully reconstructed.
Data on φ -production obtained by the CERN NA49 experiment for central Pb+Pb collisions at 158 GeV/u are presented. Compared with pp interactions the φ -yield shows substantial strangeness enhancement: the φ /π ratio is found to increase by a factor of 2.6 ± 0.6, which is approximately the square of the K/π enhancement.
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