Statistical Model of the Early Stage of nucleus-nucleus collisions with exact strangeness conservation

The Statistical Model of the Early Stage, SMES, describes a transition between confined and deconfined phases of strongly interacting matter created in nucleus-nucleus collisions. The model was formulated in the late 1990s for central Pb+Pb collisions at the CERN SPS energies. It predicted several signals of the transition (onset of deconfinement) which were later observed by the NA49 experiment. The grand canonical ensemble was used to calculate entropy and strangeness production. This approximation is valid for reactions with mean multiplicities of particles carrying conserved charges being significantly larger than one. Recent results of NA61/SHINE on hadron production in inelastic p+p interactions suggest that the deconfinement may also take place in these reactions. However, in this case mean multiplicity of particles with non-zero strange charge is smaller than one. Thus for the modeling of p+p interactions the exact strangeness conservation has to be implemented in the SMES. This extension of the SMES is presented in the paper.