NA50 CERN Collaboration

The romanian NA50 group:
C. Alexa, V. Boldea, S. Dita, S. Constantinescu

The NA50 Collaboration is an experiment included in the SPS Fixed Target CERN Scientific Programme.

The main goal of the NA50 experiment is the study of those signals, accessible in dimuon production and theoretically correlated with the transition of the hadronic matter into a Quark Gluon Plasma, using the new conditions offer by lead beam, available at CERN-SPS at ultrarelativistic incident energy.

It is now a well established prediction from lattice Quantum Chromo-Dynamics calculations that, under extreme energy density conditions, ordinary hadronic matter will undergo a phase transition to the so-called Quark-Gluon Plasma.

The main feature of this phase of hadronic matter is that the elementary constituents of hadrons are deconfined, i.e. that quarks and gluons do not form any more individual hadrons and are free to move within the medium.

From the very beginning and before the start up of the experimental search in the field, it was pointed out that deconfinement would induce color screening which in turn would prevent J/$\Psi$ formation making of "J/$\Psi$ suppression" one of the most important signatures for Quark Gluon Plasma experimental evidence. Starting from 1986, high energy ion beams (O, S and finally Pb ) became available at CERN. They made possible the search for Quark Gluon Plasma formation in ultrarelativistic nucleus-nucleus collisions where it was believed that the required conditions could be reached at best. An extensive experimental program was carried out by NA38 collaboration studying charmonium in p-A and A-B reactions with incident protons, oxygen and sulphur ions on different nuclear targets. NA50 experiment is continuing in Pb+Pb interactions the study performed by NA38 in O and S induced reactions on different target nuclei.