A. Abdelsalam

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.

Fragmentation of 28Si nuclei in nuclear emulsion

Topology of 28Si fragmentation at 14.6 A GeV in emulsion nuclei is given. In all events, the charge of each projectile fragment is measured. We report the measurements on total and some partial reactions cross sections of 28Si interactions. The data for Z6 can be qualitatively described by a statistical percolation model. The results are discussed and compared with those obtained from 28Si at 3.7 A GeV and 32S at 200 A GeV.

Multiple fast helium fragments production from 28Si-emulsion interaction at 14.6 A GeV

The measurements of partial production cross-sections of the multiple helium fragments emitted at 14.6 A GeV 28Si–emulsion interactions are reported. The production rate of helium fragments due to fragmentation of 28Si ions is studied and compared with that obtained from different projectiles at various energies. The dependence of Nα on the mass number of the incident beams is formulated. The multiplicity distributions of the helium fragments produced in 14.6 A GeV and 3.7 A GeV 28Si aswell as 200 A GeV 32S exhibit KNO scaling. The characteristics of He-multiplicity events associated with and without projectile fragments of charge Z ≥ 3 are investigated.

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.

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.

On moments of the multiplicity events of slow target fragments in relativistic Sulfur-ion collisions

A detailed study on the multiplicity characteristics of the slow target fragments emitted in relativistic heavy-ion collisions has been carried out at ELab = 3.7A and 200A GeV using 32S projectile. The beam energy dependence of the black particles produced in the full phase space of 32S-emulsion (32S-Em) interactions on the target size in terms of their moments (mean, variance, skewness and kurtosis) is investigated. The various order moments of target fragments emitted in the interactions of 32S beams with the heavy (AgBr) target nuclei are estimated in the forward (FHS) and backward (BHS) hemispheres. The investigated values of ratio of variance to mean at both energies show that the multiplicity distributions (MDs) are not Poissonian and the strongly correlated emission of target fragments are in the forward directions. The degree of anisotropic fragment emission and nature of correlation among the emitted fragments are investigated. The energy dependence of entropy is examined in both hemispheres. The entropy values normalized to average multiplicity are found to be energy independent. Scaling of MD of black particles produced in these interactions has been studied to verify the validity of scaling hypothesis via two scaling (Koba–Nielsen–Olesen (KNO)-scaling and Hegyi-scaling) functions. A simplified universal function has been used in each scaling to display the experimental data.

Target size dependence of relativistic hadron emission from 32S nuclear collisions at 3.7 and 200A GeV

The behavior of the relativistic hadron (shower particle) multiplicity for 32S–nucleus interactions is investigated. The experiment is carried out at 3.7A GeV (Dubna energy) and 200A GeV (SPS energy) to search for the incident energy effect on the interactions inside the different emulsion target nuclei. Data are presented in terms of the number of emitted relativistic hadrons in both forward and backward angular zones. The dependence on the target size is presented. For this purpose the statistical events are separated into groups according to the interactions with H, CNO, Em, and AgBr target nuclei. The separation of events, into these groups, is executed based on predictions of Glaubers multiple scattering theory. Features suggestive of a decay mechanism seem to be a characteristic of the backward emission of relativistic hadrons. The results strongly support the assumption that the relativistic hadrons may already be emitted during the de-excitation of the excited target nucleus, in a behavior like that of compound nucleus disintegration. Regarding the limiting fragmentation hypothesis beyond 1 GeV, the target size is the main parameter affecting the backward production of relativistic hadrons. The backward shower particle multiplicity can indicate the impact parameter. The incident energy is a principle factor responsible for the forward relativistic hadron production, implying that this system of particle production is a creation system. However, the target size is an effective parameter as well as the projectile size considering the geometrical concept seen in the nuclear fireball model. The forward shower particle multiplicity distributions may behave in a similar trend at Dubna energy and SPS for low target sizes. For heavy target sizes, the SPS energy reveals the creation of hadrons with nearly equal probabilities over a wide range of multiplicity, extending to more than 300 hadrons per event. The data are analyzed in the framework of the FRITIOF model.

Pion emission in α-particle interactions with various targets of nuclear emulsion detector

The behavior of relativistic hadron multiplicity for 4He-nucleus interactions is investigated. The experiment is carried out at 2.1 A and 3.7 A GeV (Dubna energy) to search for the incident energy effect on the interactions inside different emulsion target nuclei. Data are presented in terms of the number of emitted relativistic hadrons in both forward and backward angular zones. The dependence on the target size is presented. For this purpose the statistical events are discriminated into groups according to the interactions with H, CNO, Em, and AgBr target nuclei. The separation of events, into the mentioned groups, is executed based on Glaubers multiple scattering theory approach. Features suggestive of a decay mechanism seem to be a characteristic of the backward emission of relativistic hadrons. The results strongly support the assumption that the relativistic hadrons may already be emitted during the de-excitation of the excited target nucleus, in a behavior like that of compound-nucleus disintegration. Regarding the limiting fragmentation hypothesis beyond 1 A GeV, the target size is the main parameter affecting the backward production of the relativistic hadron. The incident energy is a principal factor responsible for the forward relativistic hadron production, implying that this system of particle production is a creation system. However, the target size is an effective parameter as well as the projectile size considering the geometrical concept regarded in the nuclear fireball model. The data are analyzed in the framework of the FRITIOF model.

Features about pion production in 2.1A and 3.7AGeV 4He–nucleus interactions up to and out of kinematical limit

The shower particle multiplicity characteristics are studied in 2.1A and 3.7A GeV 4He interactions with emulsion nuclei. The dependencies on emission direction, energy, target size, and centrality are examined. The data are compared with the simulation of the modified FRITIOF model. The forward emitted pion multiplicity distributions exhibit KNO scaling. The decay or peaking shaped curves characterize the pion multiplicity distributions. The decay shape is suggested to be due to a single source contribution and the peaking one results from a multisource superposition. The forward emitted pion is created from fireball or hadronic matter. The target nucleus is the origin of the backward one, regarding the nuclear limiting fragmentation hypothesis.