  Ratios of cumulants of net proton-number fluctuations measured by the STAR
Collaboration show strong deviations from a skellam distribution, which should
describe thermal properties of cumulant ratios, if proton-number fluctuations
are generated in equilibrium and a hadron resonance gas (HRG) model would
provide a suitable description of thermodynamics at the freeze-out temperature.
We present some results on sixth order cumulants entering the calculation of
the QCD equation of state at non-zero values of the baryon chemical potential
(mu_B) and discuss limitations on the applicability of HRG thermodynamics
deduced from a comparison between QCD and HRG model calculations of cumulants
of conserved charge fluctuations. We show that basic features of the
$\mu_B$-dependence of skewness and kurtosis ratios of net proton-number
fluctuations measured by the STAR Collaboration resemble those expected from a
O(mu_B^2) QCD calculation of the corresponding net baryon-number cumulant
ratios.
