Abstract
We present measurements of and production at midrapidity from Au+Au collisions at nucleon-nucleon center-of-mass energies , 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 . These ratios as a function of transverse momentum fall on a consistent trend at high collision energies, but start to show deviations in peripheral collisions at , 27, and 39 GeV, and in central collisions at 11.5 GeV in the intermediate region of GeV/. We further evaluate empirically the strange quark distributions at hadronization by studying the ratios scaled by the number of constituent quarks (NCQ). The NCQ-scaled ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to 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.
- Received 25 June 2015
- Revised 25 September 2015
DOI:https://doi.org/10.1103/PhysRevC.93.021903
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