Examining the influence of hadronic interactions on the directed flow of identified particles in RHIC Beam Energy Scan energies using UrQMD model

TL;DR

This study uses the UrQMD model to analyze how hadronic interactions influence the directed flow of various particles in heavy ion collisions across different energies, revealing the importance of hadronic phase duration on flow characteristics.

Contribution

It introduces a detailed investigation of the impact of hadronic interaction duration on directed flow patterns in heavy ion collisions at RHIC energies using the UrQMD model.

Findings

Energy dependence of $dv_{1}/dy$ varies among particle species.

Sign reversal of proton $dv_{1}/dy$ depends on collision energy and hadronic phase duration.

Charge-dependent $dv_{1}/dy$ shows strong centrality dependence.

Abstract

The directed flow of identified particles can serve as a sensitive tool for investigating the interactions during initial and final states in heavy ion collisions. This study examines the rapidity-odd directed flow ($v_{1}$) and its slope ($dv_{1}/dy$) for $\pi^{\pm}$, $K^{\pm}$, p, and $\bar{\mathrm p}$ in Au+Au collisions at different collision centralities and beam energies ($\sqrt{s_{\mathrm NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV) using the UrQMD model. We investigate the impact of late-stage hadronic interactions on charge dependent $v_{1}(y)$ and its slope by modifying the duration of the hadronic cascade lifetime ($\tau$). The energy dependence of $dv_{1}/dy$ for p ($\bar{\mathrm p}$) exhibits distinct pattern compared to $\pi^{\pm}$ and $K^{\pm}$. Notably, we observe a change in the sign reversal position of proton $dv_{1}/dy$ at different beam energies with varying $\tau$ in central and mid-central collisions. Moreover, the difference in $dv_{1}/dy$ between positively and negatively charged hadrons ($\Delta dv_{1}/dy$) demonstrates a stark centrality dependence for different particle species. The deuteron displays a significant increase in $dv_{1}/dy$ with increasing $\tau$ compared to p and n. This investigation underscores the importance of considering the temporal evolution and duration of the hadronic phase when interpreting the sign reversal, charge splitting of $v_{1}$ and light nuclei formation at lower RHIC energies.