The target mass dependence, α,on the yield of charged particles as a function of pseudorapidity n has been investigated for p, 16O and 32S induced central collisions at 200A GeV. It is pointed out that α(η) ≤ 0.4 if we only consider the simple linear superposition of nucleon-nucleon collisions. The experimental data α→1 in the target fragmentation region show the importance of nonlinear collective effect even at present incident energy. Our results from a hydrodynamical model can describe the target mlass dependence we...
