E. A. Shaat

Multiplicities of forward?backward particles in 32S?emulsion interactions at 4.5 A GeV/c

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.

Multiplicity and rapidity density in central collisions of 4.1 A GeV c-1 22Ne nuclei in nuclear emulsions

The multiplicity and pseudo-rapidity distributions of hadrons produced in central collisions of 4.1 A GeV c-1 22Ne nuclei in nuclear emulsion are studied. The KNO scaled multiplicity distribution of the produced hadrons is compared with the predicted distributions according to the Lund model, dual parton model (DPM) and the negative binomial law. The negative binomial method seems to offer a better representation of the experimental data at 4.1 A GeV c-1. The energy density is calculated according to the Bjorken model and found to be less than the estimated energy density required for the transformation into the quark-gluon plasma phase.

Nuclear multifragmentation of and in emulsion nuclei

The fragmentation of (3.7 A GeV) and (14.6 A GeV) is investigated as a function of the degree of disintegration of different components of photoemulsion nuclei. The experimental measurements show nearly energy-independent behaviour throughout the studied charge, size and multiplicity distributions of fragments produced from the two projectile beams. The various stages of the interactions, from the initial impact through to the final formation of clusters, are theoretically treated as follows. (i) The first stage of the interaction is modelled by the Glauber approach, using Reggeon parametrization for the nucleon-nucleon scattering amplitude. (ii) The additional inelastic interaction of secondary particles, produced in the primary stage, with other nucleons of the nucleus is analysed in the framework of a Reggeon-theory inspired model. (iii) The phenomenological percolation-evaporation model is used to describe the spectator part of the nucleus.

Target-Associated Particles Production in the Interactions of 3.7 and 200A GeV Sulphur Projectiles with Nuclear Emulsion

The characteristics of the associated particles produced in 3.7 and 200A GeV 32S-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.

Negative-binomial multiplicity distribution in the interactions of 24Mg ions with light and heavy emulsion nuclei

Abstract Multiplicity distributions of singly-charged particles resulting from the interactions of 4.5 GeV/ c /n 24 Mg ions with light and heavy emulsion nuclei are analysed in terms of the negative binomial distribution (NB). It is shown that the experimental distribution for 24 MgCNO interactions agrees well with the negative binomialbution, while for 24 MgAgBr interactions the obtained results show less agreement with the NB law. Values of the parameters of these distributions are discussed.

Sulphur dissociation in nuclear emulsion at 3.7 and 200A GeV

In this work, the electromagnetic dissociation (EMD) of sulphur projectile induced by two widely differing energies in nuclear emulsions is investigated. Although the percentages of EMD events of the total numbers of studied interactions are relatively small, i.e. 5.7 and 14.4% for 3.7 and 200A GeV interactions respectively, one could extract some results out of them. The emission of a proton through the 32S(γ, p)31P channel is found to be a dominant process (43.8%) at 200A GeV whereas the single alpha emission through the 32S(γ, α)28Si channel is the dominant one (34.0%) at 3.7A GeV. Multiplicity distributions of hydrogen and helium isotopes as well as the measured probabilities for the different modes of fragmentation are studied. The comparison of the present results, from electromagnetic and peripheral nuclear interactions, indicates the effective role of the different reaction mechanisms at ultra-relativistic energy (200A GeV). The experimental inclusive cross sections of different fragmentation modes produced in the EMD of 32S ions at 200A GeV were found to be in satisfactory agreement with the predictions of the combined approach of Pshenichnov et al.

Multiplicity characteristics in relativistic 24Mg-nucleus collisions

This work is concerned with the analyses of the shower and gray particle production in 4.5 A GeV/c 24Mg collision with emulsion nuclei. The highest particle production occurs in the region of the low impact parameters. While the multiplicity of the shower particles emitted in the forward direction depends on the projectile mass number and energy, the multiplicity of the backward ones shows a limiting behaviour. The source of the emission of the forward shower particles is completely different from that of the backward ones. The target fragments are produced in a thermalized system of emission.

Some characteristics of produced particles in16O-emulsion collisions at different relativistic energies

SummaryThe charged-particle multiplicities produced in inelastic interactions of16O ions at 3.7 and 60A GeV with emulsion nuclei are investigated and compared with theoretical predictions. Results from the interaction with CNO and AgBr target nuclei are analysed in terms of negative binomial (NB) distribution. Data from other nucleus-emulsion collision experiments have been used to fit an empirically proposed relationship for the average value of total charged multiplicity as a function of the geometrically determined number of interacting nucleons.

External electron pair production in high-energy collisions

SummaryExternal electron pair production is studied in the interaction of high-energy heavy ions with nuclear emulsions. The possibility of the production of neutral bosons is examined at the two energies 3.6A GeV and 200A GeV. The data seem to suggest the production and subsequent decay of short-lived neutral bosons with lifetimes of the order of 10−16–10−15s and with masses consistent with the theoretically predicted resonances.

Characteristics of projectile fragments produced in24Mg-Em interactions at Dubna energy

SummaryWe present the basic characteristics of singly, doubly and heavily charged fragments of the incident nucleus in inelastic interactions of relativistic24Mg nuclei in nuclear emulsion. The relationship between the charge of the incident projectile nuclei and those of the projectile fragments is studied. The result reflects the importance of the charge of the incident projectiles and consequently the electromagnetic interactions in the fragmentation processes.