The enhancement of v4 in nuclear collisions at the highest densities signals a first-order phase transition
Abstract.The beam energy dependence of $v_{4}$v4 (the quadrupole moment of the transverse radial flow) is sensitive to the nuclear equation of state (EoS) in mid-central Au + Au collisions at the energy range of $ 3 < \sqrt{s_{NN}} < 30$3<sNN<30 GeV, which is investigated within the hadronic transport model JAM. Different equations of state, namely, a free hadron gas, a first-order phase transition and a crossover are compared. An enhancement of $v_{4}$v4 at $\sqrt{s_{NN}} \approx 6$sNN≈6 GeV is predicted for an EoS with a first-order phase transition. This enhanced $v_{4}$v4 flow is driven by both the enhancement of $v_{2}$v2 as well as the positive contribution to $v_{4}$v4 from the squeeze-out of spectator particles which turn into participants due to the admixture of the strong collective flow in the shocked, compressed nuclear matter.