Isospin splitting of nucleon effective mass and isospin effect in heavy-ion collisions

Two different isospin splittings of nucleon effective mass in nuclear medium as the form of m_n^*> m_p^* and m_n^*> m_p^* have been implemented in an isospin and momentum dependent transport model. Their impacts on the isospin emission in heavy-ion collisions is investigated thoroughly. It is found that the yield ratios of energetic neutrons to protons squeezed out during the compression stage of two colliding nuclides are sensitive to the isospin splitting. The elliptic flows of free nucleons are also to be promising observables for extracting the nucleon effective mass splitting. Further experimental measurements are being expected, in particular at the CSR-CEE platform in Lanzhou. Several observables are proposed for constraining the density dependence of symmetry energy, such as the transverse flow difference of neutrons and protons, double ratios of n/p and π^-/π⁺, excitation functions of π^-/π⁺ and K⁰/K⁺. (author)