Target and projectile fragmentations in 208Pb-emulsion collisions at 160A GeV.

Abstract

We present the results of a study performed on the $^{208}\mathrm{emulsion}$ interactions at 160A GeV. In a minimum-bias sample of 1034 nuclear collisions, charges are assigned to all of the emitted 3431 helium and 1820 heavier projectile fragments during the breakup of the $^{208}\mathrm{Pb}$ beam in emulsion. Multiplicity distributions of the target-associated slow-moving particles and of the fast-moving projectile fragments are investigated. The polar angles of a subsample of 337 interactions having at least four projectile fragments of charge Z\ensuremath{\ge}2 are accurately measured and their pseudorapidity distributions are obtained. Multiplicity distributions, two- and three-body asymmetries, and conditional moments of the fast-moving projectile particles are investigated in terms of the total charge remaining in bound in the multiply charged projectile fragments. The results are compared with our existing 10.6A GeV $^{197}\mathrm{emulsion}$ data obtained in experiment No. 875 conducted at the Brookhaven National Laboratory. Multiplicity distributions of slow particles emitted from the $^{208}\mathrm{\ensuremath{-}}$ and $^{197}\mathrm{induced}$ emulsion reactions are found to be independent of the beam masses and their energies. An insignificant number of fission events is observed in this work. Some differences in the average yields of helium nuclei and heavier fragments are observed, which may be attributed to an energy effect or to the limited statistics. However, two- and three-body asymmetries and conditional moments indicate that the breakup mechanism of the projectiles over a wide span of energies seems to be energy independent. \textcopyright{} 1996 The American Physical Society.