Strange hadron production in Au plus Au collisions at √SNN=7.7, 11.5, 19.6, 27, and 39 GeV

We present STAR measurements of strange hadron (K-S(0), Lambda, (Lambda) over bar, Xi(-), (Xi) over bar (+), Omega(-), (Omega) over bar (+), and phi) production at midrapidity (vertical bar y vertical bar < 0.5) in Au + Au collisions at root S-NN = 7.7-39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios (<(Lambda)over bar>/Lambda, (Xi) over bar (+)/Xi(-), (Omega) over bar (+)/Omega(-)) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (mu(B)/T-ch and mu(S)/T-ch) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors (R-CP) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The K-S(0) R-CP shows no suppression for P-T up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The (Lambda) over bar /K-S(0) ratio also shows baryon-to-meson enhancement at intermediate p(T) (approximate to 2.5 GeV/c) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.