| Studying the nature of an extreme high temperature and high-density region ofnuclear matter produced by two nuclei collide with each other at very high energy is themain research in relativistic heavy ion collision experiments. HBT is an importantobservable quantity that can be used to detect the information about space-timedimensions and the dynamical evolution of the source. People find that, in a longcollision energy region, there exists a phenomenon that the HBT radii decrease with thetransverse momentum increasing. A further research suggests that the negativedependence of transverse momentum is caused by a collective expansion flow in thesource.In this dissertation, we will give a detail about the effect of the collective flow onthe HBT radii dependence of transverse momentum, by using a Blast-Waveparameterization model, which can be used to generate event with a specific collectiveflow. During the research, we find the space-momentum correlation caused bycollective flow leads to a radial direction tendency freeze out, which is more obvious ina higher transverse momentum region. A bigger collective flow leads to a strongerspace-momentum correlation. A further analysis about the comparison of HBT radii inevents with different flow provides that the dependence of Rout、Rside on transversemomentum is caused by space-momentum correlation, which is the result of collectiveflow. Strong correlation caused by big flow make the dependence strong. We also findthat pions decayed from resonance have a collective expansion tendency along theradial direction, thus space-momentum correlation, when the collective flow is set0c inthe model. The dependence ofRout、Rside on transverse momentum extracted frompions will become sharper after including the pions decayed by resonance. A majority ofpions from resonance decays is far from the center of source, which makes HBT radiiextracted by pions include resonance decays is bigger than not. |
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