A schematic representation of the QCD phase diagram. The green line and band shows the $\mu_{\rm B}$ region accessible to Lattice QCD calculations ~. The line shows the pseudocritical temperature, whereas the band represents the half-width of the crossover transition i.e. the temperatures where the QGP and hadrons can co-exist. The open points show experimental results for the determination of the chemical freeze-out parameters~. The location of atomic nuclei is also shown, as well as conjectured regions for the presence of a first order phase transition and of a critical point.