Dependance of n/p-ratio in spectator matter on the energy and mass of colliding nuclei

The Abrasion-Ablation Monte Carlo for Colliders (AAMCC) model is used to study the $n/p$-ratio of free spectator nucleons in collisions of relativistic nuclei. The calculated centrality dependence of the $n/p$-ratio is compared with the experimental data for collisions of 158A GeV $^{208}$ Pb nuclei with $^{208}$Pb target nuclei collected in the NA49 experiment at CERN SPS. For collisions of carbon, copper, xenon and gold nuclei at the NICA collider at $\sqrt{s_{NN}}=5$ GeV, the $n/p$-ratio is investigated as a function of masses of colliding nuclei. The universality of the $n/p$-ratio is demonstrated for various collision energies. The impact of the evaporation of nucleons from excited spectator matter on $n/p$-ratio is also investigated. The obtained results can be used to determine collision centrality on the basis of the composition of spectator matter in the MPD experiment at NICA and in the ALICE experiment at the LHC.