Order of the QCD transition and QCD sum rules

We propose using the finite-temperature ρ-meson mass as an order parameter to monitor the QCD transition. This is suggested by the ρ-meson mass formula that emerges from finite-temperature QCD sum rules in the vector channel, and which encompasses the effects of both quark and gluon condensates. We find that a second-order chiral-restoring transition implies a second-order behavior for the ρ mass even if the value of the gluon condensate is unaffected by the transition.