| Lattice QCD calculation predicts that when the temperature of the system increases or the hadron density increases,the nuclear matter may undergo a phase transition,changing from hadronic degrees of freedom to quark and gluon degrees of freedom,and the quark confinement effect will disappear.This state of matter is called quark gluon plasma(QGP).The relativistic heavy ion collision can simulate the QGP generation in the early state of the Big Bang,and the nuclear matter changes phase from hadron phase to quark gluon plasma.Different areas of the phase diagram can be accessed by changing the energy of the collision beam.In order to find the energy threshold to establish the QGP phase,find the signal of the first-order phase transition,and find the critical point,RHIC-STAR performed Beam Energy Scan I(BES-I),recording the central-of-mass energy of 7.7,11.5,19.6,27,39,62.4 and 200GeV collision events.The STAR detector of the Relativistic Heavy Ion Collider on the basis of BES-1 supplemented the collision event with a central-of-mass energy of 54.4GeV.According to these collision events,the BBC detector is used to reconstruct the event plane in this thesis,and the event plane method is used to calculate the rapidity-odd direct flow measurement of p,p,?+,?-,K+and K-.The results of each identified particle and net particle are compared with the results of STAR BES-I.Collective flow is one of the important observations in the relativistic heavy ion collision.It was formed in the initial period of system evolution and is very sensitive to the evolutionary nature of the system in the initial period.It is an important observable to judge whether QGP exists in the early evolution of the heavy ion collision system.The measurement of the direct flow at various energies provides us with a new perspective to understand the phase structure and characteristics of nuclear matter generated in relativistic heavy ion collisions. |
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