Strangeness in STAR at RHIC

TL;DR

This paper reports on strangeness production in heavy-ion collisions at RHIC, revealing insights into the partonic stage, collective flow, and medium properties across different energies.

Contribution

It provides new measurements of strange particle flow and nuclear modification factors, indicating changes in medium properties at lower collision energies.

Findings

Similar flow patterns for multi-strange baryons and mesons at 200 GeV.

Breaking of mass ordering suggests less hadronic interaction for phi mesons.

Significant changes in R_CP and baryon/meson ratios below 19.6 GeV.

Abstract

We present the recent results of strangeness production at the mid-rapidity in Au + Au collisions at RHIC, from $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV. The $v_2$ of multi-strange baryon $\Omega$ and $\phi$ mesons are similar to that of pions and protons in the intermediate $p_T$ range (2 - 5 GeV/$c$) in $\sqrt{s_{\rm NN}}$ = 200 GeV Au + Au collisions, indicating that the major part of collective flow has been built up at partonic stage. The breaking of mass ordering between $\phi$ mesons and protons in the low $p_T$ range ($<$ 1 GeV/$c$) is consistent with a picture that $\phi$ mesons are less sensitive to later hadronic interaction. The nuclear modification factor $R_{\rm CP}$ and baryon to meson ratio change dramatically when the collision energy is lower than 19.6 GeV. It suggests a possible change of medium property of the system compared to those from high energies.