Approaches in centrality measurements of heavy-ion collisions with forward calorimeters at MPD/NICA facility

Abstract

Abstract The MPD/NICA heavy-ion experiment is now under construction at JINR, Dubna, Russia. The centrality is the global characteristic of the nuclear interactions and reflects the degree of the nuclei overlapping or the number of interacting nucleons. One of the methods to measure the centrality is the determination of the number of non-interacting projectile fragments (spectators) which will be detected by the hadron calorimeters (FHCal) placed at the opposite sides of the beam interaction point. Since the bound spectators escape in beam holes, the central and peripheral collisions have the same spectator’s energy deposition in FHCal. It leads to the ambiguity in the determination of the collision centrality. To resolve this ambiguity a few approaches are developed based on the Monte-Carlo simulations with a few fragmentation models. The methods are based on the combination of both the spatial and the energy distributions of the spectators in the FHCal modules. A few observables for the centrality determination are constructed. Calculation of the transverse/longitudinal energies and the two-dimensional fit of the energy distributions in the FHcal modules make possible the separation of the central and peripheral events. The accuracy of the centrality measurements for a few fragmentation models is estimated.