الفهرس 
History of High Energy Nucleus-Nucleus CollisionsOnly 14 pages are availabe for public view
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Abstract
Abstract
Multiparticle production (MP) is an important experimental phenomenon in high-energy nucleus-nucleus collisions. The most features of MP such as the average charged particle multiplicity and particle densities are of fundamental interest as their variations with the collision energy, impact parameter and the collision geometry are very sensitive to the underlying mechanism involved in the nuclear collisions.
In this thesis, the emulsion technique is used to study fragmentation and particle production in the inelastic nuclear reactions induced by 118 GeV (3.7A GeV) 32S ions with emulsion nuclei.
Through a total scanned length of 80.13 meters, a number of 868 inelastic events were observed, such that the experimental mean free path, λexp = 9.23±0.31 cm. It is observed also that the values of λexp for 32S projectiles at the lowest (3.7A GeV- Dubna energy) and the highest (200A GeV- CERN energy) available energies seem to be approximately equal within experimental error.
The search for mechanisms responsible for the production of different secondary charged particles, normally known as shower and target associated fast (grey) and slow (black) particles, in the full phase space as well as in two different regions of phase space (that is the forward hemisphere (FHS) and backward hemisphere (BHS)) is performed. For the sake of comparison, the findings of this study have been compared with results of earlier experiments having different projectiles at the same incident energy and/or different energies for the same projectile.
The multiplicity distributions MDs, average multiplicity values and multiplicity correlations of different types of emitted particles are performed. The measurements of ratio of variance to mean show that the production of target fragments at high energies cannot be considered as a statistically independent process. However, the deviation of each multiplicity distribution from a Poisson law gives an evidence for correlations.
The MDs of the secondary charged particles have been fitted well with the Gaussian distribution function. With increasing the target size, MDs of different secondary charged particles become broader and extend to higher multiplicity values.
The shower particles emitted in FHS are strongly dependent on projectile mass number and energy. The shower particles emitted in BHS show no dependence on projectile mass number and energy. So, their source of production is completely different from that of forward ones.
Investigations of the mean values of target associated fragments in the FHS are found to be larger than those in the BHS, irrespective of the size or the incident energy of the projectile. The degree of anisotropic fragment emission and nature of correlation among the emitted fragments are investigated as well, indicating that the nature of the MDs of target fragments in the forward and backward directions is different.
The average multiplicities of the different charged projectile fragments (singly, doubly and multiply charged PFs) are measured for 32S projectiles at both incident energies (3.7A and 200A GeV). The emission of these PFs seems to be energy independent. Moreover, the correlations between the mean multiplicities of secondary charged particles and both of the singly and doubly charged PFs are observed.
Scaling of MDs of fast, ψg(z) and slow, ψb(z) target fragments emitted in the 32S-AgBr collisions at 3.7A and 200A GeV and in the 16O-AgBr collisions at 60A and 200A GeV have been studied to verify the validity of scaling hypothesis via two scaling (Koba-Nielsen-Olesen (KNO)-scaling and Hegyi-scaling) functions. The scaling function seems to qualitatively describe the trend of the multiplicity distribution of target fragments produced in nucleus-nucleus (AA) collisions similar to that found in hadron-hadron (hh) and hadron-nucleus (hA) collisions.
of grey particles has been fitted well with the Gaussian distribution function, but it was limited compatibility with statistical model predictions. The angular distribution shows peaking behavior at θg ˂ 90○ (FHS) while in BHS (θg ≥ 90○) the distribution shows a decay shape. This implies that the emission in BHS will occur at a later stage of a decay system after the emission of the forward particles.
The angular distribution for the fast protons emitted in the interactions of 32S-Em at 3.7 A GeV is nicely described by e0.96 cosθ, which observed in proton-induced interactions up to incident energies of 800 GeV. This observation reveals that the angular distribution of g-particles is energy independent and seems to be independent of the projectile.
The pseudo-rapidity distribution of the produced grey particles is investigated to study the characteristics of the emitted system of grey particles with respect to different target sizes. The measurements of half widths in all pseudo-rapidity distributions have approximately the same value.
The temperature of the system emitting g-particles (hot system) is predicted in the light of the proposed statistical model to be T ≈ 60 MeV.
An empirical factor linking the half widths of rapidity and the pseudo-rapidity distributions is deduced, that may be used to estimate the system temperature of emitting fast target protons at Dubna energy