Abnormal flow of α particles in heavy-ion collisions at intermediate energies

The experimentally observed abnormal $\ensuremath{\alpha}$ flow behavior from heavy-ion collisions at intermediate energies is investigated using the events of $^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$ at 35 MeV/nucleon simulated with an improved antisymmetrized molecular dynamics model with specific consideration of the Fermi motion in the nucleon-nucleon collision process. Its possible origins in the processes from the fragment formation to the experimental flow extraction, i.e., dynamical process, sequential decay, experimental detection, and data analysis, are closely examined. It is found that the observed abnormal $\ensuremath{\alpha}$ flow behavior originates from the reconstruction of reaction planes in the flow extraction. How the abnormal $\ensuremath{\alpha}$ flow behavior is generated from the reaction plane reconstruction procedure is discussed.