  Starting from the experimental evidence that high-energy nucleus-nucleus
collisions cannot be described in terms of superpositions of elementary
nucleon-nucleon interactions, we analyze the possibility that memory effects
and long-range forces imply a nonextensive statistical regime during high
energy heavy ion collisions. The relevance of these statistical effects and
their compatibility with the available experimental data are discussed. In
particular we show that theoretical estimates, obtained in the framework of the
generalized nonextensive thermostatistics, can reproduce the shape of the pion
transverse mass spectrum and explain the different physical origin of the
transverse momentum correlation function of the pions emitted during the
central Pb+Pb and during the p+p collisions at 158 A GeV.
