Charged Multiplicities at Sps and Rhic and Consequences for J/ψ Suppression 1 Charged Multiplcities in the Dual Parton Model

Hadron multiplicities in nucleus–nucleus interactions are calculated in the Dual Parton Model and its dependence on the number of collisions and the number of participants is analyzed. Shadowing corrections are calculated as a function of impact parameter and the multiplicity per participant as a funtion of centrality is found to be in agreement with experiment at SPS and RHIC energies. The obtained results are used to compute the J/ψ suppression in a comover approach. In the Dual Parton Model (DPM) the charged multiplicity per unit rapidity in a symmetric collision is given by 1 dN ch AA dy (y, b) = n A (b) N qq P −q T v µ (y) + N q P v −qq T µ (y) + (2k − 2)N qs−¯ qs µ + n(b) − n A (b) 2k N qs−¯ qs µ (y). (1) Here P and T stand for the projectile and target nuclei, n(b) is the average number of binary collisions and n A (b) the average number of participants of nucleus A. These quantities can be computed in a Glauber model. k is the average number of inelastic collisions in pp and µ(b) = kn(b)/n A (b) is the total average number of collisions suffered by each nucleon. In the DPM each inelastic collision leads to two strings and the total number of strings is 2kn. The charged multiplicity produced by a single string is obtained by a convolution of momentum distribution functions and fragmentation function, and it depends on µ due to energy conservation. We see from (1) that the multiplicity is given by a linear combination of n A and n with coeficients which depend on the impact parameter b (via µ(b)).