  It is shown that the Geant4 FTF model, which does not include the simulation
of the hard parton-parton scattering and the formation of the quark-gluon
plasma (QGP), describes well the NA61/SHINE data on $\pi^-$ meson distributions
for the interactions at $\sqrt{s_{NN}}=$ 5.2, 6.1, 7.6 and 8.8 GeV. At higher
energies, $\sqrt{s_{NN}}=$ 11.9 and 16.8 GeV, the model underestimates the
data. This is considered as an indication of the formation of QGP at higher
energies in central collisions of light and intermediate nuclei than in
collisions of heavy nuclei ($\sqrt{s_{NN}}\sim 6$ GeV).
