Speaker
Description
$\quad$Heavy-ion collisions provide a unique opportunity to study the properties of the QCD matter at varying temperatures, densities and system volumes. $\Omega$ and $\phi$ hadrons, composed merely of strange quarks, have relatively small hadronic interaction cross sections and can be utilized to study the matter properties at its early stage. In Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, significant $\Omega$ enhancement over $\phi$ have been observed at intermediate transverse momentum in central collisions, which can be explained by their productions through coalescence of strange quarks in Quark-Gluon Plasma (QGP). Hence the energy threshold of QGP production (or onset of deconfinement) in heavy ion collisions can be explored by measuring the colliding energy dependence of $\Omega/\phi$ enhancement. It can also be expected that the measurement of $\Omega/\phi$ ratios in different colliding systems may indicate the minimum colliding system size required to produce QGP.
$\quad$ In this talk, we will present new measurements of strange hadron production in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 9.2, 11.5, 14.6, 17.3 and 19.6 GeV using high statistics STAR BES-II data. The transverse momentum ($p_T$) spectra, centrality dependence of yields, nuclear modification factor and the particles ratios ($\phi/K$ ) will be presented. In particular, the energy and centrality dependence of $\Omega$/$\phi$ ratios in BES-II energy range will be presented. Besides, the $\Omega/\phi$ ratios in smaller colliding systems including O+O, d+Au, and isobar collisions at $\sqrt{s_{NN}}$ = 200 GeV will also be shown and compared to the Au+Au data at the same colliding energy. These results will be compared to theoretical calculations and physics implications will be discussed.
