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An attempt is made to study various types of multiplicity distributions and multiplicity correlations amongst secondary charged particles produced in 4.5 and 14.5 A GeV/c 28 Si-nucleus interactions. The results reveal that multiplicity correlations of the type j i n n − , where i, j = b, g, s and h with i ≠ j, are linear. The observed multiplicity correlations are nicely fitted by the method of least squares fitting of the type, j n = b + an i. Furthermore, the multiplicity distributions of relativistic charged particles and compound multiplicity at 4.5 A GeV/c are nicely fitted by Poisson distributions with peaks at relatively lower multiplicities. However, in the case of multiplicity distributions of various types of secondary charged particles produced in 14.5 A GeV/c 28 Si-nucleus collisions definite trends are not discernible.

Nuclear collisions at FAIR energies are envisaged to produce net-baryon densities ≈ 5 -6 times higher than the normal nuclear matter density. At such high densities, baryons start melting into their constituents, the quarks and gluons, forming a mixed or even deconfined medium. Such a state will be explored experimentally at the upcoming Facility for the Antiproton and Ion Research (FAIR). In such collisions, production of multi-strange hadrons plays a major role in investigating the characteristics of the medium. Enhanced production of strange quarks and therefore, of (anti)hyperons is believed to be an important signature of the formation of partonic medium.The yields of (anti)hyperons have been investigated in the at 40 AGeV -top FAIR SIS300 energy using the hadronic-string model (UrQMD) and hadronic and partonic modes of the transport model (AMPT). It is seen that multi-strange (anti)hyperons are very sensitive to the partonic medium and the enhancement is very dominant at FAIR energy.

Event by event fluctuations of particle multiplicities and of their ratios are considered to be sensitive probes to the exotic phenomena in high energy heavy ion collisions like phase transition or the critical point. A phenomenon of interest might take place at a particular time as per the fulfillment of the required conditions and the observables sensitive to the fluctuations will therefore be non-monotonic at that particular time. Experimentally, fluctuations however are measured only at freeze-out. In this work, using the hybrid version of the UrQMD event generator, we have investigated the propagation of event by event fluctuations of the ratio of particle multiplicities, their ratios and of the ratio of total positive and negative charges in Au+Au collisions at E lab ≤ 90 AGeV. A commonly used experimental measure ν dyn has been used in this analysis. The hybrid model, i.e., UrQMD with hydrodynamic evolution has been used to study the effect of hydrodynamic evolution on this conventional fluctuation measure. It is observed that the fluctuations as measured by ν dyn get diluted considerably during the evolution till freeze-out. The dominant structures present at the initial stage of evolution get smoothen out. The hydro version of the model with two types of equation of state shows higher fluctuation at lower collision energy as compared to the pure hadronic transport version of the model. The time evolution of the higher order moments of net-proton distributions in a specified coverage showed similar dilution with time.