Strangeness Production In Relativistic Heavy Ion Collisions In The Quark Recombination Model

The study of quark-gluon plasma contributes to explore the universe. So far, the most effective way to produce likely quark-gluon plasma is high energy heavy-ion collisions。We can consider the head-on collision of two nuclei which speed up by accelerator, then the vast energy lost by the nuclear matter is deposited in the vicinity of the center of mass of the colliding system, such as RHIC and LHC. We can probe the particles produced in the heavy ion collisions, but can not know the evolution of the collision system and the particle production mechanisms. Therefore, people construct the different models to understand the particle production process. We will introduce the quark recombination model which describe the hadronization process in high energy heavy ion collisions.Hadronization is the process of the formation of hadrons out of quarks and gluons. This occurs after high energy collisions in which free quarks or gluons are created. There are two successful classical models to describe hadronization:the string model and the independent parton fragmentation model. But both of them has certain limitations, the string model only use for describing the processes of the particles production at low pT, and the fragmentation model can only describe the processes of particle production at high pT. The quark recombination model can describe the processes of the particles production at any pT and explain the lots of experimental phenomena. For the recombination model, we consider only quark and antiquark degrees of freedom, and gluons are assumed to have been converted into quark and antiquark pairs before hadronization. The partons produced in high energy collisions includes two parts:thermal partons and shower partons. For the recom-bination model introducing the hadronization time, the production rates for mesons and baryons are proportional to square and cubic of the quark density, this ensures the unitarity of collision system. The recombination model helps us to understand the mechanism of particles production in heavy ion collisions.The strangeness enhancement is one of the signals of producing likely of the quark-gluon plasma. We consider the strangeness production in relativistic heavy ion collisions in the quark recombination model. We are working in u, d, s sector and the light quarks have nonzero chemical potential. We will calculate the yields of mesons and baryons and the yield ratios between strange and non-strange hadrons for the three cases with different scenarios for the evolution of the system. The unitarity and the conservation of the number of quarks are used as the constraint on the model. We only consider the contribution to produced hadron from the recombination of thermal partons in the low pT. We show that more baryons can be produced relative to the mesons with the increase of the initial quark density, and with the increase of strange quark density, the yields of strange hadrons increase while those for non-strange hadrons decrease. Strangeness enhancement is shown in three cases. We can see that the yields of baryons and mesons depend on the details of the evolution of the system and the strange quark density influences strongly on the strangeness enhancement of the system.