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

We present results for the ratios of mean (M₁), variance (₁^2), skewness (S₁) and kurtosis (₁) 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 s₍₍19. 6 GeV. We show that the difference in cumulant ratios for the mean net baryon-number, M₁/₁^2=₁^B (T, ₁) /₂^B (T, ₁), and the normalized skewness, S₁₁=₃^B (T, ₁) /₂^B (T, ₁), naturally arises in QCD thermodynamics. Moreover, we establish a close relation between skewness and kurtosis ratios, S₁₁^3/M₁=₃^B (T, ₁) /₁^B (T, ₁) and ₁₁^2=₄^B (T, ₁) /₂^B (T, ₁), valid at small values of the baryon chemical potential.