Universality in High Energy Collisions of small and large systems

TL;DR

This paper discusses the universal behavior observed in high energy collisions across different system sizes, highlighting how parton density influences phenomena like strangeness enhancement and collective flow, suggesting a common underlying mechanism.

Contribution

It introduces a unified framework based on parton density to explain collective phenomena in both small and large collision systems.

Findings

Universal behavior emerges when considering parton density as the initial condition.

Collective effects are observed in small systems like proton-proton collisions.

Electron-positron annihilation energies are too low for collective phenomena.

Abstract

Strangeness enhancement and collective flow are considered signatures of the quark gluon plasma formation. These phenomena have been detected not only in relativistic heavy ion collisions but also in high energy, high multiplicity events of proton-proton and proton-nucleus (small systems) scatterings. A universal behavior emerges by considering the parton density in the transverse plane as the dynamical quantity to specify the initial condition of the collisions, which in electron-positron annihilation at the available energies is too low to expect collective effects.