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Register a new userRelativistic Nuclear Collisions and the QCD Phase Boundary
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P. Braun-Munzinger
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In nucleus-nucleus collisions at ultra-relativistic energies matter is formed with initial energy density significantly exceeding the critical energy density for the transition from hadronic to partonic matter. We will review the experimental evidence for this new form of matter - the Quark-Gluon Plasma - from recent experiments at the SPS and RHIC with emphasis on collective behavior, thermalization, and its opacity for fast partons. We will further show that one can determine from the data a fundamental QCD parameter, the critical temperature for the QCD phase transition.
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We update briefly our understanding of hadron production in relativistic nucleus-nucleus collisions in terms of statistical models with emphasis on the relation of the data to the QCD phase boundary and on a puzzle in the beam energy dependence.
We present measurement of elliptic flow, $v_2$, for charged and identified particles at midrapidity in Au+Au collisions at $sqrt{s_{NN}}$ = 7.7 - 39 GeV. We compare the inclusive charged hadron $v_2$ to those from transport model calculations, such as UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in $v_2$ between particles and anti-particles. The $v_2$ of $phi$ meson is observed to be systematically lower than other particles in Au+Au collisions at $sqrt{s_{NN}}$ = 11.5 GeV.
We present phi-meson transverse momentum distribution as well as its elliptic flow (v_{2}) measurements in Au + Au collisions at center-of-mass energy per nucleon pair sqrt{s_{NN}} = 7.7, 11.5 and 39 GeV with the data taken from STAR experiment at RHIC in the year 2010. We discuss the energy dependence of phi-meson elliptic flow (v_{2}) and central-to-peripheral nuclear modification factors (R_{CP}). The v_{2} of phi-mesons are compared to those from other hadron species. The implications on partonic-hadronic phase transition are discussed.
We summarize our current understanding of the connection between the QCD phase line and the chemical freeze-out curve as deduced from thermal analyses of yields of particles produced in central collisions between relativistic nuclei.
The spinodal amplification of density fluctuations is treated perturbatively within dissipative fluid dynamics for the purpose of elucidating the prospects for this mechanism to cause a phase separation to occur during a relativistic nuclear collision. The present study includes not only viscosity but also heat conduction (whose effect on the growth rates is of comparable magnitude but opposite), as well as a gradient term in the local pressure, and the corresponding dispersion relation for collective modes in bulk matter is derived from relativistic fluid dynamics. A suitable two-phase equation of state is obtained by interpolation between a hadronic gas and a quark-gluon plasma, while the transport coefficients are approximated by simple parametrizations that are suitable at any degree of net baryon density. We calculate the degree of spinodal amplification occurring along specific dynamical phase trajectories characteristic of nuclear collision at various energies. The results bring out the important fact that the prospects for spinodal phase separation to occur can be greatly enhanced by careful tuning of the collision energy to ensure that the thermodynamic conditions associated with the maximum compression lie inside the region of spinodal instability.
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