Lessons from PHOBOS

TL;DR

The PHOBOS experiment at RHIC collected extensive collision data across various nuclei and energies, revealing simple dependencies and strong correlations in particle production, but no comprehensive model yet explains all observed phenomena.

Contribution

This paper summarizes the extensive findings from PHOBOS data, highlighting simple energy and centrality dependencies and correlations in particle production in heavy ion collisions.

Findings

Global properties depend on energy and centrality

Strong correlations observed among produced particles

No single model fully explains the phenomenology

Abstract

In June 2005 the PHOBOS Collaboration completed data taking at RHIC. In five years of operation PHOBOS recorded information for Au+Au at $\sqrt{s_{NN}}$ = 19.6, 62.4, 130, and 200 GeV, Cu+Cu at 22.4, 62.4 and 200 GeV, d+Au at 201 GeV, and p+p at 200 and 410 GeV, altogether more than one billion collisions. Using these data we have studied the energy and centrality dependence of the global properties of charged particle production over essentially the full 4$\pi$ solid angle and (for pions near mid rapidity) charged particle spectra down to transverse momenta below 30 MeV/c. We have also studied correlations of particles separated in pseudorapidity by up to 6 units. We find that the global properties of heavy ion collisions can be described in terms of a small number of simple dependencies on energy and centrality, and that there are strong correlations between the produced particles. To date no single model has been proposed which describes this rich phenomenology. In this talk I summarize what the data is explicitly telling us.