Fluctuations and Correlations in hadron-hadron and nucleus-nucleus collisions and String Percolation

Forward-Backward correlations in pp(pp̄) and Nucleus-Nucleus collisions are discussed in the framework of the string percolation model. The point we want to stress is that such correlations, at low energy, increase with energy and the number of participants, at high energies they are extected to decrease with energy and the number of participating nucleons. At RHIC and LHC these predictions can be tested. 1Introduction Recent results on multiplicity fluctuations in Au−Au collisions, sNN = 62 and 200 GeV, at RHIC by the PHENIX collaboration [1], and not so recent ones by the NA49 collaboration [2] at the SPS, √ sNN = 19.5 GeV, using different nuclei (from p to Pb), show the following: i) The distribution of charged particles, negatively charged particles and positively charged particles, for a fixed number of participating nucleons, Npart, is, in good approximation, a Negative Binomial Distribution (NBD); ii) The NBD k parameter, Departamento de F́ısica, IST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal CENTRA, Departamento de F́ısica, IST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal