  We show that a measurement of the reaction energy dependence of relative
hadron resonance yields in heavy ion collisions can be used to study the phase
structure of the dense QCD matter created in these collisions, and investigate
the origin of the trends observed in the excitation functions of certain soft
hadronic observables. We show that presence of chemical nonequilibrium in light
quark abundance imparts a characteristic signature on the energy dependence of
resonance yields, that differs considerably from what is expected in the
equilibrium picture.
