On wounded constituents in nuclear collisions

Abstract

Abstract. In this talk we summarize the main results of our recent paper [1], where we explore predictions of the wounded quark model for particle production and the properties of the initial state formed in ultra-relativistic collisions of atomic nuclei.Particle-particle interactions at high energies usually lead to copious production of new particles whose number rises as a function of the collision energy. The charged particle multiplicity (N ch ) and its pseudorapidity density (dN ch /dη) are fundamental measurable quantities which serve as important characteristics of the global properties of the system. The data on production of particles in relativistic collisions of atomic nuclei collected during the operation of RHIC [2,3] and the LHC [4] accelerators indicate that the standard wounded nucleon model [5] (according to the definition, a wounded nucleon is the one which underwent at least one inelastic collision) does not describe the observed centrality dependence of particle multiplicities in the A+A collisions, unless a component proportional to the binary collisions [6] is added.We are interested in the impact of subnucleonic components of matter on the dynamics of the of the early stage of the collisions, and explore th wounded quark model [10][11][12][13]. One of the interesting results of [1] is that taking into account subnucleonic degrees of freedom in the description of the early phase of the collision one obtains the linear dependence of production of particles as a function of the number of wounded constituents, namelywhere Q W is the number of wounded constituents involved in the collision. Such scaling has been suggested in [14] for the RHIC data. The wounded quark scaling also works for the SPS energy range [15]. More recent studies were reported in [16][17][18][19].Our results for particle production at midrapidity are shown in Fig. 1. We note an approximately flat centrality dependence of dN ch /dη/Q W in qualitative agreement with the earlier studies [8,14,15,20]. In contrast, the flatness is not the case in the wounded nucleon model, where, as is well known, the ratio dN ch /dη/N W substantially increases with the number of wounded nucleons, N W . The value of dN ch /dη/Q W (i.e., the average number of charged hadrons per unit of rapidity coming from a single Presented by M. Rybczyński a