Directed flow of $\Lambda$ in high-energy heavy-ion collisions and $\Lambda$ potential in dense nuclear matter

TL;DR

This study examines how the directed flow of $ ext{Lambda}$ hyperons in high-energy heavy-ion collisions is influenced by their potential in dense nuclear matter, using theoretical models and experimental data to explore the properties of hot, dense matter.

Contribution

It demonstrates that the $ ext{Lambda}$ directed flow is sensitive to the momentum dependence of the potential, providing insights into the dense matter created in collisions, and compares different theoretical approaches.

Findings

$ ext{Lambda}$ potentials from $ ext{chiral EFT}$ reproduce experimental flow data.

Directed flow is insensitive to density dependence but sensitive to momentum dependence.

Hydrodynamics and quark coalescence models predict different hyperon flow behaviors.

Abstract

We investigate the sensitivity of the $\Lambda$ directed flow to the $\Lambda$ potential in mid-central Au + Au collisions at $\sqrt{s_{NN}}\approx3.0$--$30$ GeV. The $\Lambda$ potential obtained from the chiral effective field theory ($\chi$EFT) is used in a microscopic transport model, a vector version of relativistic quantum molecular dynamics (RQMDv). We find that the density-dependent $\Lambda$ potentials, obtained from the $\chi$EFT assuming weak momentum dependence of the potential, reproduce the rapidity and the beam-energy dependence of the $\Lambda$ directed flow measured by the STAR collaboration in the Beam Energy Scan program. Although the $\Lambda$ directed flow is insensitive to the density dependence of the potential, it is susceptible to the momentum dependence. We also show that a hydrodynamics picture based on the blast-wave model predicts a similarity of the proton, $\Lambda$, and $\Xi$ directed flows, but the directed flow of $\Omega$ baryons slightly deviates from other baryons. We also show that the quark coalescence predicts different rapidity dependence of the directed flows for hyperons. These investigations suggest that measurements of a wide range of the rapidity dependence of the directed flow of hyperons may provide important information about the properties of hot and dense matter created in high-energy heavy-ion collisions.