C. Pajares

PERCOLATION APPROACH TO QUARK-GLUON PLASMA AND J/PSI SUPPRESSION

It is shown that the critical threshold for percolation of the overlapping strings exchanged in heavy ion collisions can naturally explain the sharp strong suppression of {ital J}/{psi} shown by the experimental data on central Pb-Pb collisions, which does not occur in central O-U and S-U collisions. {copyright} {ital 1996 The American Physical Society.}

Multiple production in the Monte Carlo string fusion model

The influence of the string fusion on the basic features of relativistic heavy-ion collisions is studied with the help of a Monte Carlo string fusion model. The model is based on the parton picture of strong interactions and includes the string fusion phenomenon. It is demonstrated that string fusion leads to a considerable reduction of particle production with a relative enhancement of the baryon component in AA collisions at ultra-relativistic energies

Nuclear effects in J/ψ suppression

Abstract We compute the effect on the J/ψ production in nucleus-nucleus coollisions of the absorption of the J/ψ inside the colliding nuclei. Using a value of the absorptive J/ψ-nucleon cross section which reproduces the A -dependence of the J/ψ cross section in hadron-nucleus collisions, we obtain much less suppression than that measured by the NA38 Collaboration. The effect due to a strongly absorbed ( A 0.7 ) component is also discussed. In order to explain the NA38 results one needs a very large contribution (50%) of the latter component.

Implications of color-string percolation on multiplicities, correlations, and the transverse momentum

In the colour string model the impact of string percolation on multiplicities, their long-range correlations and average transverse momentum is studied. The multiplicities are shown to be damped by a simple factor which follows from the percolation theory. A clear signature of the phase transition is found to be a behaviour of the correlations for intensive observables, such as average transverse momentum, which can be detected in the high-energy heavy ion collisions.

Percolation of strings and the relativistic energy data on multiplicity and transverse momentum distributions

The dependence of the multiplicity on the number of collisions and the transverse momentum distribution for central and peripheral Au-Au collisions are studied in the model of percolation of strings relative to the experimental conditions at RHIC. The comparison with the first RHIC data shows a good agreement.

Long range forward–backward correlations and the color glass condensate

Abstract We discuss forward–backward correlations in the multiplicity of produced particles in heavy ion collisions. We find the color glass condensate generates distinctive predictions for the long range component of this correlation. In particular, we predict the growth of the long range correlation with the centrality of the collision. We argue that the correlation for baryons is less strong than that for mesons.

Correlations between multiplicities and average transverse momentum in the percolating color strings approach

Abstract.Long range multiplicity-multiplicity, pT2-multiplicity and p2T- p2T correlations are studied in the percolating color string picture under different assumptions of the dynamics of the string interaction. It is found that the strength of these correlations is rather insensitive to these assumptions; nor is it sensitive to the geometry of the fused string clusters that formed, the percolation phase transition in particular. Both multiplicity-multiplicity and pT2-multiplicity correlations are found to scale and depend only on the string density. pT2-multiplicity correlations, which are absent in the independent string picture, are found to be of the order of 10% for central heavy ion collisions and can serve as a clear signature of string fusion. In contrast p2T- p2T correlations turned out to be inversely proportional to the number of strings and therefore to be very small for realistic collisions.

Monte Carlo model for nuclear collisions from SPS to LHC energies

Abstract. A Monte Carlo model to simulate nuclear collisions in the energy range going from SPS to LHC is presented. The model includes in its initial stage both soft and semihard components, which lead to the formation of color strings. Collectivity is taken into account considering the possibility of strings in color representations higher than triplet or antitriplet, by means of string fusion. String breaking leads to the production of secondaries. At this point, the model can be used as an initial condition for the further evolution by a transport model. In order to tune the parameters and see the results in nucleus–nucleus collisions, a naive model for rescattering of secondaries is introduced. Results of the model are compared with experimental data, and predictions for RHIC and LHC are shown.

Universality of the transverse momentum distributions in the framework of percolation of strings

Abstract.In the framework of percolation of color sources, the transverse momentum distribution in heavy ion and p + p collisions at all centralities and energies are shown to follow a universal behavior. The width of the distribution depends on the fluctuations of the number of color sources per cluster. At low densities, there are only independent single color sources, no fluctuations occur and the distribution is described by a single exponential. At very high densities, only one cluster of many color sources appears and therefore there are not fluctuations either and the hardness of the distribution is suppressed. The Cronin effect in this framework is due to a maximum of the fluctuations which decreases as the density increases. We obtain a good agreement with experimental data including the low pT behavior and the spectra for different particles. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. This point is satisfied by the experimental data on p + p collisions at different energies.

String and parton percolation

Abstract.A brief review to string and parton percolation is presented. After a short introduction, the main consequences of percolation of color sources on the following observables in A-A collisions: