  Higher order moments of net conserved charge fluctuations, in particular net
baryon number and net electric charge, are sensitive thermodynamic observables
that respond strongly to critical behavior in strong interaction matter. In
order to use them also as a sensible probe to detect critical behavior in heavy
ion experiments we not only need to better understand the relation between
chemical freeze-out in heavy ion collision and the QCD phase boundary, we also
need to verify that charge fluctuations measured experimentally indeed
correspond to thermal conditions as described by equilibrium QCD. This requires
a model independent characterization of thermal conditions for which cumulants
of conserved charge fluctuations themselves are ideally suited.
