Does non-monotonic behavior of directed flow signal the onset of deconfinement?

Abstract

We investigate the effects of nuclear mean-field as well as the formation and decay of nuclear clusters on the directed flow v 1 in high energy nucleus-nucleus collisions from √ s NN = 7.7 GeV to 27 GeV incident energies within a transport model. Specifically, we use the JAM transport model in which potentials are implemented based on the framework of the relativistic quantum molecular dynamics. Our approach reproduces the rapidity dependence of directed flow data up to √ s NN ≈ 8 GeV showing the significant importance of mean-field. However, the slopes of dv 1 /dy at mid-rapidity are calculated to be positive at √ s NN = 11.7 and 19.6 GeV, and becomes negative above 27 GeV. Thus the result from the JAM hadronic transport model with nuclear mean-field approach is incompatible with the data. Therefore within our approach, we conclude that the excitation function of the directed flow cannot be explained by the hadronic degree of freedom alone.

Beam energy dependence of the squeeze-out effect on the directed and elliptic flow in Au + Au collisions in the high baryon density region

“…In this work, we use the parameter set used in Ref. [60], which yields the nuclear incompressibility of K = 272 MeV. As a second approach, we control the pressure of the system by changing the scattering style in the two-body collisions [42].…”

“…shows the beam energy dependence of directed flow as a function of rapidity for nucleons (left panel) and pions (right panel) from 6.4 to 62.4 GeV obtained by the cascade mode. One may refer Refs [31,60]. for the comparison with the STAR data at midrapidity with different EoS.…”

Effects of mean-field and softening of equation of state on elliptic flow in Au+Au collisions at $\sqrt{{s}_{\rm{NN}}}=5\,\mathrm{GeV}$ from the JAM model

“…The parameters α, β, γ, ρ 0 , C 1 , C 2 , µ 1 , µ 2 are taken from Ref. [42]. We also study the effect of the softening of EoS on elliptic flow by the method of choosing attractive orbit in two-body scattering [43].…”

High Density EOS — Heavy-Ion Collisions, Compact Stars and Strangeness —

“…Skyrme-type density dependent and Lorentziantype momentum dependent nuclear mean field of baryons are included based on the framework of simplified version of relativistic quantum molecular dynamics (RQMD/S) in Ref. [11], but with slightly different parameter sets which yields the incompressibility of K = 272 MeV [22]. The hadronic transport model with momentum dependent mean field describes the directed flow data in the corresponding energy region better [11,19].…”