Directed flow of isospin sensitive fragments within a modified clusterization algorithm in heavy-ion collisions

By extending the minimum spanning tree (MST) clusterization algorithm for the binding energy cut, the isospin asymmetry dependence of directed flow for isospin sensitive isobar pairs (neutrons-protons, ³H-³He) is studied from low towards high incident energies. The modified clusterization method (MSTB) has the advantage to identify the fragments at quite early time. It enhances (reduces) the production of free nucleons (fragments) over MST method. The directed flow of isobaric pair ³H-³He is more sensitive towards isospin asymmetry caused by MSTB than isobaric pair n-p. This sensitivity becomes quite strong towards the high incident energy and neutron-rich reaction system. In conclusion, the inclusion of binding energy in clusterization method for the flow studies has been uniquely important for understanding the isospin physics, especially for high density behavior of symmetry energy. (authors)