An exclusive study of the characteristics of the interactions accompanied by the backward emission (θLab ≥ 90°) of relativistic and fast hadrons in the collisions of 4.5 A GeV/c 32S beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward (θLab < 90°) and backward hemispheres due to the interactions with the two emulsion components (CNO, AgBr) are presented and analysed. The correlations between the multiplicities of the different emitted particles are also investigated. This study reveals that there are signatures for a collective mechanism, which plays a role in the production of particles in the backward hemisphere. Hence, the backward multiplicity distribution of the emitted shower or grey particles at 4.5 A GeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favour the idea that the backward particles were emitted due to the decay of the system in the latter stage of the reaction. While the mean values of the shower particles emitted in the forward hemisphere ⟨nfs⟩ are strongly dependent on the projectile size and incident energy, the mean value of the multiplicity of the shower particles flying into the backward hemisphere ⟨nbs⟩ are found to be only a function of the target size (i.e. impact parameter). Therefore, the results yield quite interesting information regarding the mechanism of the backward particle production in heavy ion interactions. The present data are believed to support the mechanism, which considers the backward particle production as a consequence of the isotropic decay of a highly excited target system, in its rest frame, after the forward particle emission.

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The characteristics of the associated particles produced in 3.7 and 200A GeV 32 S -emulsion inelastic interactions are reported. The experimental data at 3.7 A GeV are compared with the predictions of the standard cascading evaporation model. For explaining the results at higher energy (200A GeV), a simple model which includes the nucleon sub-structure (Reggeon model) is introduced. This model is found to be capable of producing the mean features of the data obtained for the two used exposures.

An experimental study of the forward and backward emission of relativistic and fast hadrons in the interactions of 4.5 A,GeV/c 32S with emulsion was carried out. The study supports the conclusion that a collective mechanism is responsible for the production of particles in the backward hemisphere (which is restricted beyond the kinematics limit). The backward emission of both shower and grey particles can be described by an exponential decay law independent of the projectile size. The experimental results suggest that the backward particles result from the decay of the system in a latter stage of the interaction. While the average multiplicities of the shower particles emitted in the forward hemisphere are strongly dependent on the projectile size and incident momentum, the average values of those emitted into the backward hemisphere are found to be only a function of the target size (i.e., impact parameter). Thus, the backward particle production can be considered as a yield of a highly excited target system, in its rest frame.PACS Nos.: 25.75.–q, 25.75.Dw, 25.75.Gz, 25.75.Ld, 25.70.Mn, 25.70.Pq,41.75.Ak, 41.75.Cn, 29.40.Rg, 07.68.+m

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