Probing Parton Dynamics of QCD Matter with $\hat{I}\text{c◯}$ and $\ddot{I}•$ Production

Abstract

We present measurements of $\hat{I}\text{c◯}$ and $\ddot{I}•$ production at mid-rapidity 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 Relativistic Heavy Ion Collider (RHIC). Motivated by the coalescence formation mechanism for these strange hadrons, we study the ratios of $N(\hat{I}{\text{c◯}}^{-}+\hat{I}{\text{c◯}}^{+})/(2N(\ddot{I}•))$. 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 2.4-3.6 GeV/c. We further evaluate empirically the strange quark $p_T$ distributions at hadronization by studying the $\hat{I}\text{c◯}/\ddot{I}•$ ratios scaled by the number of constituent quarks. The NCQ-scaled $\hat{I}\text{c◯}/\ddot{I}•$ ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to $\sqrt{s_{NN}}>=19.6$ 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.

7 pages, 5 figures