System scan of the multiplicity correlation between forward and backward rapidities in the relativistic heavy-ion collisions by using a multi-phase transport model

A systematic study on forward-backward (FB) multiplicity correlations from large systems to small ones through a multi-phase transport model (AMPT) has been performed and the phenomenon that correlation strength increases with the centrality can be explained by taking the distribution of events as the superposition of a series of Gaussian distributions. It is also found that correlations in the η - Φ plane can imply the shape of event. Furthermore, long range correlations originate from the fluctuations associated with the source information. FB correlations allow us to decouple long range correlations from short range correlations, and may provide a chance to investigate the $\alpha$-clustering structure in initial colliding light nuclei as well. It seems the tetrahedron $^{16}$O + $^{16}$O collision gives a more uniform and symmetrical fireball, after that emits the final particles more isotropically or independently in the longitudinal direction, indicating that the forward-backward multiplicity correlation could be used to identify the pattern of $\alpha$-clustered $^{16}$O in future experiments.