Strangeness Production And J/ψ Polarization Study In High Energy Heavy-ion Collisions

The main motivation for colliding heavy ions at maximal achievable energy is to study the properties of the hadrouic matter under extreme high temperature and matter density. It is believed that eventually \ve will reach sufficient temperature or baryon density to produce a new state of matter-quark gluon plasma(QGP). The study of the pha.se transition from ordinary hadronic matter to QGP. and to further investigate the properties of QGP has been the major effects of these experiments at SPS/CERN. AGS/BNL and RHIC/BNL. This thesis is focused on the study of strangeness production in heavy-ion collisions via LUCIAE model and the J./ polarization at RHIC.This thesis is organized in two parts: The first part of this thesis focuses on strangeness production at SPS energies. The strange baryon and strange meson pro-duction at SPS energies are modeled via LUCIAE model which includes the reseat ter-ing. the collective interaction between strings and the reduced strange quark production mechanism.LUCIAE model can describe the yield and the transverse mass spectra of produced strangeness. The model reproduced the following facts of WA97 experimental data: the yield of strange particles increases with increasing mass and increasing centrality of the colliding system, and also with increasing strangeness content of hyperons in relativis-tic nucleus-nucleus collisions. The simulation of strangeness production using LUC1AE model shows that strangeness production is related not only to the rescattering. but also to the collective interaction among strings in relativistic nucleus-nucleus collisions.The o meson enhancement in p-Pb and Pb-Pb relative to p-p collisions is described consistently by LUCIAE. In this model, o mesons are exclusively produced from string fragmentation processes without any further rescattering interactions. This implies that. at the CERN SPS energy, the -mesons are mostly produced in primordial collisions and final state interactions at the hadronic stage do not play a significant, role.By widening the width of Gaussian transverse momentum distribution in string fragmentation. LUCIAE reproduced the o mesons rapidity distribution, transverse mass distribution, and also the enhancement factor of o meson in Pb-Pb relative to p-p collisions. Tinl agreement between NA49 data and LUCIAE results is improved obviously.The second part of this thesis is devoted to the J/v particle polarization study for the PHENIX/RHIC experiment. The main focus of the second part of this thesis is to explore the correct offline data analysis procedure to study the J/v polarization. It is demonstrated that one not only needs to correct the detector acceptance but also needs to correct the PT and XF distribution of the .J/v particle.One of the main goal of the PHENIX detector is to investigat the J/v production mechanism from relativistic heavy ion reaction. In order to extract the correct cos distribution of the J/v decay unions, using PYTHIA J/v events for instance, we initially develop the method to do the PHENIX detector acceptance correction. Monte Carlo J/v events were generated to make detector acceptance corrections to niuon pair angular distributions. One needs to fine tune the simulations by carefully reproducing in theVIMonte Carlo program the measured kinematic variable distributions. J/ particle of PYTHIA events is nnpolarization in Collions Soper rest frame in full PT and XF space. Corrected J/ in Collins Soper frame reproduced the polarized property of PYTHIA J/v?events.In order to simulate PHENIX detector effect, we study the PYTHIA events and Monte Carlo events going through PISSA(P.HENIX Integrated Simulation Application). Corrected cos distribution of J/v particles in virtual photon rest frame(Collins-Sopcr) appear nnpolarized. This simulation study demonstrate a right method to do the detector acceptance correction for angular distribution.