Femtoscopic signatures of collective behavior as a probe of the thermal nature of relativistic heavy ion collisions

TL;DR

This paper investigates femtoscopic signatures of collective behavior in relativistic heavy-ion collisions, demonstrating how certain observables can distinguish between thermalized systems and alternative models.

Contribution

It identifies femtoscopic signatures that can validate the thermal nature of the matter created in heavy-ion collisions, supported by rescattering simulations.

Findings

Increased rescattering leads to more collective behavior and thermalization.

Certain femtoscopic signatures can differentiate between thermal and non-thermal models.

The results favor a thermal model with uniform temperature for the system.

Abstract

Femtoscopy measures space-time characteristics of the particle emitting source created in relativistic heavy-ion collisions. It is argued that collective behavior of matter (radial flow) produces specific femtoscopic signatures. The one that is best known, the m_T dependence of the pion ``HBT radii'', can be explained by the alternative scenario of temperature gradients in an initial state thermal model. We identify others that can invalidate such alternatives, such as non-identical particle correlations and m_T scaling for particles of higher mass. Studies with a simple rescattering code show that as the interaction cross-section is increased the system develops collective behavior and becomes more thermalized at the same time, the two effects being the natural consequence of increased number of particle rescatterings. Repeating calculations with a more realistic rescattering model confirmed all of these conclusions and provided deeper insight into the mechanisms of collectivity buildup, showing a preference for a thermal model with uniform temperature.