Intermediate mass dimuons in NA38/NA50

Le résumé fourni par la source

The NA38/NA50 experiments have measured, at the CERN SPS, the dimuon production in proton--nucleus and nucleus--nucleus collisions. In this paper it is shown that the mass continuum between the $\phi$ and the $J/{\psi}$ can be satisfactorily described, after having removed the combinatorial background due to uncorrelated $\pi$ and $K$ decays, as a sum of two contributions, namely the Drell--Yan process and the semi--leptonic decay of pairs of charmed mesons, whose mass shape in the acceptance of the experiment has been evaluated using PYTHIA. However, in order to describe the A--B (namely S--U and Pb--Pb) mass spectra, the dimuon yield from open charm decays, which in p--A collisions is found to be consistent with direct open charm measurements from other CERN and FNAL experiments, has to be enhanced with respect to a linear extrapolation of p--A results. The size of the enhancement smoothly increases from peripheral S--U to central Pb--Pb interactions, reaching a factor $\sim$ 3 in central Pb--Pb collisions. The $p_T$ distributions of the events in the mass continuum are also compatible with the hypothesis of open charm enhancement in A--B collisions.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.