Neutron-proton effective mass splitting in a Boltzmann-Langevin approach

Based on the Boltzmann-Langevin transport model, in which the isospin and momentum-dependent potential is incorporated, we investigate the neutron-proton effective mass splitting in central reactions using Sn isotopes at 50 MeV/nucleon. It is found that the transverse momentum, rapidity, and kinetic energy distributions of free neutron over proton ratio are sensitive to the neutron-proton effective mass splitting, especially at higher transverse momenta, at higher kinetic energies, and at larger rapidities. The calculated results favor the effective mass of neutrons less than the one of protons in comparison with the experimental data of Famiano et al. [Phys. Rev. Lett. 97, 052701 (2006), 10.1103/PhysRevLett.97.052701].