Impact-parameter dependences of the number of interacting nucleons and mean multiplicities in heavy-ion collisions

The impact-parameter dependence of the mean number of interacting nucleons in high-energy heavy-ion collisions is considered in the case of identical atomic weights of colliding nuclei and in the case where one nucleus is much heavier than the other. It is shown that the use of a rare event—for example, an event of J/ψ or ? production—as a trigger may change significantly quantities representing the averages of the multiplicities for accompanying secondaries over impact-parameter values. The multiplicities of accompanying particles in central collisions can have but a slight dependence on the trigger. The observed multiplicity ratios for various secondaries in central and minimum-bias events can be used as a test in searches for quark-gluon plasma.