Experimental Study Of Elliptic Flow Of Multi-strange Hadron (?) In Au+Au Collisions At (?)=54.4 GeV With RHIC/STAR Detector

The phase structure of high-temperature and high-density nuclear matter is a hotspot and frontier in the field of nuclear physics research.The main physical goal of the Rela-tivistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory in the United States is to study the properties and phase structure of high-temperature and high-density nuclear matter,and to find the critical point of QCD phase transition.RHIC conducted the first phase of the heavy ion collision energy scan(Beam Energy Scan-I,BES-I)experiment from 2010 to 2014.Its main goal is to scan the QCD phase diagram by changing the colli-sion energy of the Au+Au.And use sensitive experimental observations to find the QCD phase transition critical point signal.In the RHIC BES-I experiment,the centroid energy per nucleon pair can reach 7.7-200 GeV,and the corresponding baryon chemical potential range is about 420-20 MeV.The experimental results confirmed the appearance of Quark-Gluon Plasma(QGP)in the RHIC highest energy heavy ion collision experiment.The collective motion behavior in heavy ion collisions is studied by measuring the Fourier expansion anisotropy parameter vn of the azimuth distribution of the final state particle relative to the reaction plane.The elliptic flow v2 discussed in this article is the second term of the anisotropy parameter vn.Since the elliptic flow comes from the pressure gradient generated by the spatial anisotropy in the initial state of the collision system,its magnitude depends on the strength of the interaction during the evolution of the system,and can provide effective degree of freedom in the system formed by the early heavy ion collision、information on temperature and thermodynamic parameters.In this article,we measured(?)54.4 GeV in Au+Au collisions with multi-strange hadrons Ξ elliptic flow(in 2017,the STAR detector supplemented the Energy points on the basis of the BES-I experiment).Multi-strange particles have smaller hadron scatter-ing cross sections,which are mainly produced in the early stage of heavy ion collisions.Therefore,when studying the properties of nuclear matter produced by early collisions,multi-strange hadrons are superior to light-flavored quark(u,d)particles,and strange par-ticle probes.Studying the elliptic flow of strange particles and the Number-of-constituent quark(NCQ)scaling of v2 can help us determine whether the elliptic flow of hadrons is formed in the quark level before hadronization.In this article,we discussed the depen-dence of the Ξ elliptic flow on different centrality and pT.analyzed the dependence of the difference between the Ξ-particle and its antiparticle Ξ+elliptic flow with the collision energy,and studied NCQ of multi-strange particle Ξv2.The experimental results show that the multi-strang hadron elliptic flow v2 has a strong dependence on its transverse momentum and centrality,and its magnitude increases with the increase of the transverse momentum pT,and the elliptic flow in the center-to-center collision is smaller than the elliptic flow in the edge collision.The difference between the Ξ-and Ξ+ elliptic flow currents will decrease with the increase of collision energy.The size of the elliptic flow of Ξ is similar to that of the light quark elliptic flow.β particle elliptic flow conforms to the number of constitient quark scaling.In this paper,the significant elliptic flow of Ξ provides strong evidence for the collective motion of the parton.The results of NCQ of v2 in the experiment can indicate that the system has been in the deconfined state prior to hadronization.,and reached the quark degree of freedom at(?)=54.4GeV Au+Au collisions.