Directed flow of $\Lambda$, $\bar{\Lambda}$, $K^{\pm}$, $K_S^0$ and $\phi$ mesons from Beam Energy Scan Au+Au collisions using the STAR experiment

TL;DR

This study measures the directed flow of various particles in Au+Au collisions across multiple energies, revealing energy-dependent sign changes and similarities that inform the understanding of the quark-gluon plasma and collision dynamics.

Contribution

It provides new measurements of directed flow for multiple particle species over a range of collision energies, highlighting energy-dependent behavior and differences between particles and antiparticles.

Findings

Sign change in $dv_1/dy$ of $ ext{Lambda}$ near 11.5 GeV.

Similar $v_1$ slope trends for $ar{ ext{Lambda}}$, $ar{p}$, and $ ext{phi}$ at high energies.

Deviations in net proton and net kaon $dv_1/dy$ at low energies.

Abstract

We report the results of $v_1$ and $dv_1/dy$ near mid-rapidity for $\Lambda$, $\bar{\Lambda}$, $K^{\pm}$, $K_s^0$ and $\phi$ in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7, 11.5, 14.5, 19.6, 27 and 39~GeV using the STAR detector at RHIC. The $dv_1/dy$ of $\Lambda$ is found to be consistent with that of the proton and shows a change in sign near $\sqrt{s_{\rm NN}} = 11.5$~GeV. The $v_{1}$ slope for $\bar{\Lambda}$, $\bar{p}$ and $\phi$ shows a similar trend for $\sqrt{s_{\rm NN}}$ $>$ 14.5~GeV, while below 14.5~GeV, $\phi$ $v_{1}$ is consistent with zero but with a large uncertainty. The $dv_{1}/dy$ for net protons and net kaons is similar for $\sqrt{s_{\rm NN}} >$ 14.5~GeV, but they deviate at lower beam energies.