Heavy Mesons Distribution At Low Transverse Momentum Region In High-energy Collisions

In high-energy heavy ion collisions,in order to analyse the physical process in the early stage,the study of the multiplicity and transverse momentum is significant.Due to the asymptotic freedom of QCD,the theoretical calculation based on pQCD is consistent with the experimental date in high P_Tregion.However,there exits a disagreement at low P_T.In this paper,we propose a new method–the system hot bath model–to describe the multiplicity of mesons at low P_T.We regard pions as hot bath oscillators and heavy mesons as system particles.We consider the interaction between pions and heavy mesons,so as to analyse the multiplicity of heavy mesons.Our results shows a good agreement with the experimental date of J/?and D mesons in the low P_Tregion.The system hot bath model is a mixing of a small system with a large hot bath,where the particles in the hot bath are regarded as harmonic oscillators.The vibration of the harmonic oscillators will induce to vibration of the particles in the small system.The dynamic evolu-tion can be obtained through Langevin equations.For example,the Brownian motion of pollen molecules putted in to bath liquid can be described with this model.Previous studies show that in the high-energy heavy ion collision,the system composed of low-P_Tproduced particles can be considered in the delicate-balance equilibrium.Since most of the produced particles are pions,we will consider them as hot bath oscillators,and the small amount of produced heavy mesons such as J/?,D,are regarded as system particles.We can look the produced particles system as system hot bath model.If we analyze the multiplicities of the produced heavy mesons such as J/?and D,we will find that they are not Bose distributed,however,they obey abnormal diffusion rule.The factors to induce abnormal diffusion come the following:1.the interaction among the particles inside the system.2.the external influence outside the system.Because the amount of produced heavy mesons are small,and the distance are large,the interaction among the heavy mesons to cause the abnormal diffusion can be neglected.Therefore,we propose a new physical mechanism,the abnotmal diffusion of heavy mesons at low-P_Tcomes from the dy-namical effect from pions.Through analysing the abnormal diffusion distribution of pions from the experimental data,we obtain the modified transverse momentum equation which reflects the interaction of pions at different centrality,we put it into system hot bath model and obtain the transverse momentum equation of heavy mesons through the Hamiltonian equation of the sys-tem hot bath model.We confirm the parameters through the experimental data of J/?and reach the multiplicity of heavy meson theoretically.The result shows a good agreement between our theoretical result and experimental data.This dissertation are introduced as the following parts:in the first part,the relevant back-ground and research status of this field will be introduced;in the second part,we will introduce the knowledge of system hot bath model,Brownian motion and abnormal diffusion used in this paper;in the third part,we will focus on the physical process and calculation details of the work,give numerical analysis results and compare with the experimental measurement results;we will summarize in the forth part.