New probe to study the symmetry energy at low nuclear density with the deuteron breakup reaction

The reactions of nucleons and polarized deuterons scattered off a heavy target nucleus at large impact parameter with intermediate energies have been investigated by using the improved quantum molecular dynamics model. It is found that, due to the opposite effects of isovector potential on protons and neutrons, there is a significant difference between the angle distributions of elastically scattered protons and neutrons. To overcome the lack of a monochromatic neutron beam, the reaction of polarized deuterons peripherally scattered off a heavy target nucleus is used to replace the reaction of individual protons and neutrons scattered off a heavy target nucleus to study the isospin effect. It is found that the distributions of the scattering angle of the proton and the neutron originating from the elastic breakup of the deuteron are very similar to the results of the individual proton- and neutron-induced reactions. A new probe more effective and more clean, namely the difference between the elastic scattering angle of the proton and that of the neutron originating from the breakup of the polarized deuteron, is promoted to constrain the symmetry energy at subsaturation density.