Directed flow of transported and nontransported protons in Au+Au collisions from an ultrarelativistic quantum molecular dynamics model

Abstract

The directed flow of inclusive, transported and nontransported (including produced) protons, as well as antiprotons, has been studied in the framework of an ultrarelativistic quantum molecular dynamics approach for $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=7.7$, 11.5, 19.6, 27, 39, 62.4 and 200 GeV. The rapidity, centrality, and energy dependence of directed flow for various proton groups are presented. It is found that the integrated directed flow decreases monotonically as a function of collision energy for $\sqrt{{s}_{NN}}=11.5$ GeV and beyond. However, the sign change of directed flow of inclusive protons, seen in experimental data as a function of centrality and collision energy, can be explained by the competing effect of directed flow between transported and nontransported protons. Similarly, the difference in directed flow between protons and antiprotons can be explained. Our study offers a conventional explanation on the cause of the ${v}_{1}$ sign change other than the antiflow component of protons alone, which is argued to be linked to a phase transition.