Nucleon effective mass splitting and density-dependent symmetry energy effects on elliptic flow in heavy ion collisions at Elab=0.09 ∼ 1.5 GeV/nucleon*

By incorporating an isospin-dependent form of the momentum-dependent potential in the ultra-relativistic quantum molecular dynamics (UrQMD) model, we systematically investigate effects of the neutron-proton effective mass splitting P and the density -dependent nuclear symmetry energy Esym(p) on the elliptic flow v2 in 197Au + 197Au collisions at beam energies from 0.09 to 1.5 GeV/nucleon. It is found that at higher beam energies (> 0.25 GeV/nucleon) with the approximately 75 MeV difference in slopes of the two different Esym(p), and the variation of mn*_,,, ranging from 0.03 to 0.03 at saturation density with isospin asymmetry 6 = (pn pp)Ip= 0.2, the Esym(p) has a stronger influence on the difference in v2 between neutrons and protons, i.e., v2 4, than mn*_,,, has. Meanwhile, at lower beam energies 0.25 GeV/nucleon), v2 V2 is sensitive to both the Esym(p) and the mi,*_r. Moreover, the influence of mn*_,,, on v2 -4 is more evident with the parameters of this study when using the soft, rather than stiff, symmetry energy.