Universality in Hadronic and Nuclear Collisions at High Energy

TL;DR

Recent high-energy collision experiments reveal universal behaviors across proton-proton, proton-nucleus, and nucleus-nucleus systems, suggesting common underlying dynamics related to initial entropy density and system size.

Contribution

This work highlights the universality in various observables across different collision systems, emphasizing the role of initial entropy density and fluctuations in high-energy hadronic and nuclear collisions.

Findings

Universal behavior observed in strangeness suppression and multi-strange hadron yields.

Scaling of average transverse momentum and elliptic flow across systems.

The initial entropy density correlates with observed universal patterns.

Abstract

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 $\gamma_s$ and yields of multi-strange hadrons; b)~the average transverse momentum, $p_t$, with particular attention to the low $p_t$ region where soft, non-perturbative effects are important; 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.