Probing the QGP phase boundary with thermal properties of φ mesons

A novel attempt has been made to probe the QCD phase boundary by using the experimental data for transverse momenta of φ mesons produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted with simple thermodynamic expectations and lattice QCD results. The experimental data indicate a first-order phase transition, with a mixed phase stretching the energy density between ∼1 and 3.2 GeV/fm³ corresponding to SPS energies.