Strangeness-Correlations on the pseudo-critical line in (2+1)-flavor QCD

We present some lattice QCD results on first (₁ⁱ) and second (₂ⁱ) cumulants of and correlations (₁₁^ij) among net baryon-number (B), strangeness (S) and electric charge (Q) along the pseudo-critical line (T₏₂ (B) ) in the temperature (T) --baryon chemical potential (B) phase diagram of (2+1) -flavor QCD. We point out that violations of the isospin symmetric limit of vanishing electric charge chemical potential are small along the T₏₂ (B) for the entire range of B covered in the RHIC beam energy scan. For the strangeness neutral matter produced in heavy-ion collisions this leads to a close relation between ₁₁^BS and ₁₁^QS. We compare lattice QCD results for ₁₁^BS/₂S along the T₏₂ (B) line with preliminary experimental measurements of ₁₁^BS/₂S for collision energies 7. 7~ GeV s_₍₍ 62. 4~ GeV. While we find good agreements for s_₍₍ 39~GeV, differences are sizeable at smaller values of s_₍₍. Moreover, we compare lattice QCD results for the ratio of the strangeness (S) to baryon (B) chemical potentials, which define a strangeness neutral system with fixed electric charge to baryon number density, with experimental results obtained by the STAR collaboration for S/B using strange baryon yields on the freeze-out line. Finally, we determine the baryon chemical potential at the freeze-out (Bᶠ) by comparing ₁B/₂B along the T₏₂ (B) with the experimentally measured net-proton cumulants ₁ᵖ/₂ᵖ. We find that \Bᶠ, T₏₂ (Bᶠ) \ are consistent with the freeze-out parameters of the statistical-model fits to experimentally measured hadron yields for s_₍₍ 11. 5 GeV.