Disentangling effects of nucleon size and nucleus structure in relativistic heavy-ion collisions

While relativistic heavy-ion collisions become an alternative way of studying nucleus structure, the accurate extraction of nucleus structure could be hampered by the uncertainty of nucleon size, and the latter has attracted people's attention in the past few years. We have compared the impacts of nuclear size and nucleus structure on deformation probes in relativistic heavy-ion collisions based on a multiphase transport (AMPT) model. With increasing nucleon size, the absolute values of the deformation probes are generally reduced due to smeared initial density fluctuations. In heavy systems such as $^{197}$Au+$^{197}$Au collisions, neglecting the nucleon size could underestimate or overestimate significantly the extracted deformation parameter depending on the used deformation probe, while the scaled anisotropic flow and the scaled Pearson correlation coefficient of flow and transverse momentum are good probes of the nucleus deformation rather insensitive to the nucleon size. In small systems such as $^{16}$O+$^{16}$O collisions, the deformation probes are generally more sensitive to the nucleon size than to the nucleus structure, and the transverse momentum fluctuation less sensitive to detailed nucleus structure may serve as a good probe of the nucleon size.