Type: Article
Publication Date: 2016-02-24
Citations: 52
DOI: https://doi.org/10.1103/physrevc.93.021903
We present measurements of $\mathrm{\ensuremath{\Omega}}$ and $\ensuremath{\phi}$ production at midrapidity from Au+Au collisions at nucleon-nucleon center-of-mass energies $\sqrt{{s}_{NN}}=7.7, 11.5, 19.6$, 27, and 39 GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC). Motivated by the coalescence formation mechanism for these strange hadrons, we study the ratios of $N({\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}+{\overline{\mathrm{\ensuremath{\Omega}}}}^{+})/[2N(\ensuremath{\phi})]$. These ratios as a function of transverse momentum ${p}_{T}$ fall on a consistent trend at high collision energies, but start to show deviations in peripheral collisions at $\sqrt{{s}_{NN}}=19.6$, 27, and 39 GeV, and in central collisions at 11.5 GeV in the intermediate ${p}_{T}$ region of $2.4\ensuremath{-}3.6$ GeV/$c$. We further evaluate empirically the strange quark ${p}_{T}$ distributions at hadronization by studying the $\mathrm{\ensuremath{\Omega}}/\ensuremath{\phi}$ ratios scaled by the number of constituent quarks (NCQ). The NCQ-scaled $\mathrm{\ensuremath{\Omega}}/\ensuremath{\phi}$ ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to $\sqrt{{s}_{NN}}\ensuremath{\ge}19.6$ GeV. The shapes of the presumably thermal strange quark distributions in 0--60% most central collisions at 7.7 GeV show significant deviations from those in 0--10% most central collisions at higher energies. These features suggest that there is likely a change of the underlying strange quark dynamics in the transition from quark matter to hadronic matter at collision energies below 19.6 GeV.