We study proton - anti-proton cross sections in the framework of an updated minijet eikonal model. We propose a different scheme for fixing the parameters, in which we make use of the measured minijet cross section. We compare the results obtained with the GRV98, MRST98, CTEQ6-L and KLN gluon distributions. The latter includes gluon saturation effects. We conclude that in the very high energy regime the use of the KLN distribution improves significantly the behavior of the cross sections. However this improvement is due to the shape of the KLN gluon density and has little to do with saturation effects.

The Interacting Gluon Model (IGM) is a tool designed to study energy flow, especially stopping and leading particle spectra, in high energy hadronic collisions. In this model, valence quarks fly through and the gluon clouds of the hadrons interact strongly both in the soft and in the semihard regime. Developing this picture we arrive at a simple description of energy loss, given in terms of few parameters, which accounts for a wide variety of experimental data. This text is a survey of our main results and predictions.

In this work we calculate the meson cloud effects on the pion electromagnetic form factor and perform a comparison with experimental data. We show that, even though the cloud is not the only non-perturbative process to be considered, its contribution is significant. We also study the influence of the cutoff choices on the results.

We update the calculation of c - <img id="_x0000_i1026" src="../../img/revistas/bjp/v34n1a/a19img02.gif" align=absbottom>production in the initial stage of nucleus - nucleus collisions and within quark gluon plasma, using the most recent and most accepted values for the ingredients, such as nuclear parton distributions, quark masses, couplings and fireball parameters. We find a large discrepancy in the charm yields, depending on the input choices. A global analysis of all the different cases suggests that the “in-plasma” production is a significant fraction of the total yield.

Recent DESY-HERA data on J/<FONT FACE="Symbol">Y</font> elasticity distribution show that it emerges mostly as a fast particle. Interpreting photoproduction as a collision between a pre-formed charmed hadron and the proton, the outcoming J/<FONT FACE="Symbol">Y</font> is a leading particle of the collision. We analyse these data using a model formulated to describe energy flow in hadron-hadron reactions. The measured J/<FONT FACE="Symbol">Y</font> spectrum can be successfully described in terms of this model. We conclude that the observed transparency of the charmed hadron-proton collisions arises because of the particularly small gluonic content of the initial c - <img src="http:/img/fbpe/bjp/v28n4/image200.gif" alt="Image200.gif (847 bytes)" align="absbottom"> state.