Skewness and kurtosis of net baryon-number distributions at small values of the baryon chemical potential

We present results for the ratios of mean (MB), variance (σB²), skewness (SB) and kurtosis (κB) of net baryon-number fluctuations obtained in lattice QCD calculations with physical values of light and strange quark masses. Using next-to-leading order Taylor expansions in baryon chemical potential we find that qualitative features of these ratios closely resemble the corresponding experimentally measured cumulant ratios of net proton-number fluctuations for beam energies down to √sNN≥19.6 GeV. We show that the difference in cumulant ratios for the mean net baryon-number, MB/σB²=χ₁B(T,μB)/χ₂B(T,μB), and the normalized skewness, SBσB=χ₃B(T,μB)/χ₂B(T,μB), naturally arises in QCD thermodynamics. Moreover, we establish a close relation between skewness and kurtosis ratios, SBσB³/MB=χ₃B(T,μB)/χ₁B(T,μB) and κBσB²=χ₄B(T,μB)/χ₂B(T,μB), valid at small values of the baryon chemical potential.