Probing the EOS and nn cross section by analyzing the collective flow at high and intermediate energy in the RVUU approach

Abstract

We have studied the collective flow at high and intermediate energy in a relativistic Vlasov-Uehling-Uhlenbeck (RVUU) approach based on Walecka's QHD-I model, with the aim to probe the nuclear-matter equation of state (EOS) and the in-medium nucleon-nucleon cross section σ. At high energy (1.2 GeV/u), the out-of-plane azimuthal correlation function C( Ψ) is only sensitive to the effective mass m ∗ and insensitive to the nuclear compressibility K and the effective nucleon-nucleon cross section σ within a reasonable range. We have found that the preferred value of m ∗ is about 0.85 m. With this value of m ∗ , from the in-plane mean transverse momentum 〈 P x ( Y)〉 which is sensitive to both m ∗ and σ we have drawn an effective nn cross section σ, namely σ ∼ 0.8 σ f where σ f is the free nucleon-nucleon cross section in Cugnon's parametrization. Taking advantage of the fact that the energy of vanishing flow (EVF) at intermediate energy (around 100 MeV/u) is only sensitive to the nucleon-nucleon cross section σ, we have drawn some information on the nucleon-nucleon cross section σ, namely σ = (1.4±0.2) σ f.