The time evolution of light nuclei cumulants and ratios with a first-order phase transition in the UrQMD transport model

TL;DR

This study uses the UrQMD transport model with a first-order phase transition to analyze how baryon and proton cumulants evolve over time in heavy ion collisions, revealing subtle signals of phase transition effects.

Contribution

It introduces a detailed time-dependent analysis of cumulants in heavy ion collisions with a phase transition using the UrQMD model, highlighting potential experimental signatures.

Findings

Significant deviation from Gaussian baryon fluctuations observed.

Proton fluctuations are suppressed during dense collision phases.

Small enhancement of third-order proton cumulants in large rapidity windows.

Abstract

The UrQMD model with a density dependent equation of state, including a first-order phase transition, is used to study the time dependence of baryon number and proton number susceptibilities up to third order in heavy ion reactions of $E_{\mathrm{lab}}=2-3 A$ GeV. A significant deviation from the Gaussian fluctuations of the baryon number fluctuation in coordinate space is observed. The proton number fluctuations are always suppressed as they constitute only a small fraction of the total baryon number during the dense phase of the collision. It is found that the only measurable, but small, signal would be an enhancement of the third order (or higher) proton cumulant in a finite rapidity window $\Delta y$ that is larger than one unit of rapidity. In addition, it is found that the coordinate fluctuations will lead to an enhancement of cluster production due to the correlations in coordinate space. However, this enhancement is small and mainly occurs during the dense part of the collision before the system actually freezes out.