2025/06/13 by Taseer, Muhammad Farhan, Singha, Subhash
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph) #Nuclear Experiment (nucl-ex) #Nuclear Theory (nucl-th)
paper · doi:10.48550/arxiv.2506.12114
The STAR experiment at the top RHIC energy has observed that the directed flow (v1) of inclusive light hadrons is independent of the collision system size at a given centrality~\citeSTAR:2008jgm. However, recent STAR measurements indicate a system-size dependence in the v1(y)-slope (dv1/dy) of protons, antiprotons, and their differences (Δdv1/dy) at a given centrality, suggesting a potential influence of baryon production and transport mechanisms~\citeTaseer:SQM2024talk. We have studied pseudorapidity (dN/dy) distributions and directed flow (v1 and dv1/dy) for pions, kaons, and protons in Au+Au and Cu+Cu collisions at √sNN = 19.6 GeV using the A Multi-Phase Transport (AMPT) model. Specifically, we investigated the influence of string junction parameters in AMPT via the PYTHIA/JETSET routines, focusing on the popcorn mechanism and string-splitting parameters, on dN/dy, dv1/dy, and their charge-dependent splittings (ΔdN/dy and Δdv1/dy). We observe that string junction parameters can affect dN/dy, dv1/dy, ΔdN/dy, and Δdv1/dy for π, K, and p, and influence their system-size dependence. The effect is most prominent on the v1 of protons, non-trivial for kaons, while the pions v1 remain largely unchanged. These findings provide insights into the interplay between particle production mechanisms, baryon transport, and directed flow in heavy-ion collisions.