Directed flow of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math> in high-energy heavy-ion collisions and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math> potential in dense nuclear matter

Abstract

We investigate the sensitivity of the $\mathrm{\ensuremath{\Lambda}}$ directed flow to the $\mathrm{\ensuremath{\Lambda}}$ potential in midcentral Au $+$ Au collisions at $\sqrt{{s}_{NN}}\ensuremath{\approx}3.0\text{--}30\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. The $\mathrm{\ensuremath{\Lambda}}$ potential obtained from the chiral effective field theory ($\ensuremath{\chi}\mathrm{EFT}$) is used in a microscopic transport model, a vector version of relativistic quantum molecular dynamics. We find that the density-dependent $\mathrm{\ensuremath{\Lambda}}$ potentials, obtained from the $\ensuremath{\chi}\mathrm{EFT}$ assuming weak momentum dependence of the potential, reproduce the rapidity and the beam-energy dependence of the $\mathrm{\ensuremath{\Lambda}}$ directed flow measured by the STAR collaboration in the beam energy scan program. Although the $\mathrm{\ensuremath{\Lambda}}$ 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, $\mathrm{\ensuremath{\Lambda}}$, and $\mathrm{\ensuremath{\Xi}}$ directed flows, but the directed flow of $\mathrm{\ensuremath{\Omega}}$ 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.

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