Detecting The Granularity Of Particle Emitting Source By Pion Imaging Method

In high-energy heavy-ion collisions, two-pion interferometry is an important tool to study the space-time structure of the particle-emitting sources produced in the collisions. Traditional two-pion interferometry analysis needs to make an assumption in advance for the particle-emitting source. It obtains the space-time information of the source by fitting the two-pion correlation functions with model-dependent parameterized formulas. However, pion imaging method is a model independent technique. It gets the pion source function directly from the two-pion correlation function, and then obtain the space-time and coherence information about the source. So imaging method is more suitable for analyzing the sources with non-Gaussian distributions in detail.The purpose of this paper is to obtain the space-time information of particle emitting source by pion imaging method, and detect the granularity of source. Firstly, we use HIJING (Heavy-Ion Jet Interaction Generator) to generate the initial states of the particle-emitting sources in high-energy heavy-ion collisions. We obtain the evolution of the particle-emitting source with time by the simulation code of relativistic fluid dynamics. The results indicate that the granular inhomogeneity of the HIJING initial states may survive even in the later stages of the evolution. Then, we obtain the two-pion correlation functions of the granular sources by two-pion interferometry, and extract the source functions by the imaging method. The results indicate that the two-pion source functions of the granular sources exhibit a two-tiered structure. Next, we fit the source functions obtained by the imaging method with the formulas of granular source and Gaussian source, and find that the two-tiered structure of the two-pion source functions of granular source can be fitted very well with the granular source formula. Finally, we analyze the granularity parameter ζ of the particle-emitting sources in different conditions, and find that the values of ζ can be used to describe the source granularity degree very well. The granularity of the emitting source can be detected through the analyses to ζ,.