Hadron Resonance Gas Model for An Arbitrarily Large Number of Different Hard-Core Radii

We develop a novel formulation of the hadron-resonance gas model which, besides a hard-core repulsion, explicitly accounts for the surface tension induced by the interaction between the particles. Such an equation of state allows us to go beyond the Van der Waals approximation for any number of different hard-core radii. A comparison with the Carnahan-Starling equation of state shows that the new model is valid for packing fractions 0.2-0.22, while the usual Van der Waals model is inapplicable at packing fractions above 0.1-0.11. Moreover, it is shown that the equation of state with induced surface tension is softer than the one of hard spheres and remains causal at higher particle densities. The great advantage of our model is that there are only two equations to be solved and it does not depend on the various values of the hard-core radii used for different hadronic resonances. Using this novel equation of state we obtain a high-quality fit of the ALICE hadron multiplicities measured at center-of-mass energies of 2.76 TeV per nucleon. Furthermore, using the traditional hadron-resonance gas model with multi-component hard-core repulsion and the novel one we investigate the recently suggested model in which the proper volume of a hadron is proportional to its mass. We find that the high-temperature maximum of $\chi^2/ndf$ observed in the latter model always appears in the region located far above the limit of its applicability.