Universality in hadronic and nuclear collisions at high energy
P. Castorina (INFN, Sezione di Catania, I-95123 Catania, Italy, Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic); A. Iorio (Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic); D. Lanteri (INFN, Sezione di Catania, I-95123 Catania, Italy, Dipartimento di Fisica e Astronomia, Università di Catania, I-95123 Catania, Italy); H. Satz (Fakultät für Physik, Universität Bielefeld, D-33501 Bielefeld, Germany); M. Spousta (Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic)
Recent experimental results in proton-proton and in proton-nucleus collisions at Large Hadron Collider energies show a strong similarity to those observed in nucleus-nucleus collisions, where the formation of a quark-gluon plasma is expected. We discuss the comparison between small colliding systems and nucleus-nucleus collisions, for (a) the strangeness suppression factor and yields of multi-strange hadrons; (b) the average transverse momentum, , with particular attention to the low region where soft, nonperturbative effects are important; and (c) the elliptic flow scaled by the participant eccentricity. The universal behavior in hadronic and nuclear high energy collisions emerges for all these observables in terms of a specific dynamical variable which corresponds to the entropy density of initial system in the collision and which takes into account the transverse size of the initial configuration and its fluctuations.
