Features of strangeness production in pp and heavy ion collisions

Abstract

Based on the existing experimental data for A-A collisions starting from the AGS energies up to the LHC ones, various systematics related to strange hadrons and anti-hadrons are presented. The ratio between the average transverse momentum and the square root of the total particle multiplicity per unit rapidity and unit transverse overlap area decreases with collision energy for a given centrality or with centrality for a given collision energy, thus supporting the predictions of CGC and percolation based approaches. The dependence on the square root of the total multiplicity per unit rapidity and unit transverse overlap area of the slope and offset extracted from the $\langle p_T\rangle$-particle mass correlation and of the average transverse expansion velocity and kinetic freeze-out temperature parameters obtained from BGBW fits of the pT spectra for strange hadrons is compared to that for pions, kaons and protons. The detailed study of the entropy density dependence of the ratio of strange hadron yields per unit rapidity to the total particle multiplicity per unit rapidity, at different collision energies and centralities, reveals the necessity to study separately strange hadrons and anti-hadrons. The correlation between the ratio of the single- and multi- strange anti-hadron yield per unit rapidity to the total particle multiplicity per unit rapidity and the entropy density is presented as a function of the fireball size. A maximum is evidenced in the similar correlation established for combined and separate species of strange hadrons, at different centralities, in the region where a transition from the baryon-dominated matter to the meson-dominated one takes place. The position of this maximum does not depend on the mass of the corresponding strange hadron. Comparison with pp experimental data reveals another similarity between pp and Pb-Pb collisions at the LHC energies.