Nucleon-nucleon momentum-correlation function as a probe of the density distribution of valence neutrons in neutron-rich nuclei

Proton-neutron, neutron-neutron, and proton-proton momentum-correlation functions (C-pn, C-nn, and C-pp) are systematically investigated for C-15 and other C-isotope-induced collisions at different entrance channel conditions within the framework of the isospin-dependent quantum-molecular-dynamics model complemented by the correlation after burner (CRAB) computation code. C-15 is a prime exotic nucleus candidate due to the weakly bound valence neutron coupling with closed-neutron-shell nucleus C-14. To study density dependence of the correlation function by removing the isospin effect, the initialized C-15 projectiles are sampled from two kinds of density distribution from the relativistic mean-field (RMF) model in which the valence neutron of C-15 is populated in both 1d5/2 and 2s1/2 states, respectively. The results show that the density distributions of the valence neutron significantly influence the nucleon-nucleon momentum-correlation function at large impact parameters and high incident energies. The extended density distribution of the valence neutron largely weakens the strength of the correlation function. The size of the emission source is extracted by fitting the correlation function by using the Gaussian source method. The emission source size as well as the size of the final-state phase space are larger for projectile samplings from more extended density distributions of the valence neutron, which corresponds to the 2s1/2 state in the RMF model. Therefore, the nucleon-nucleon momentum-correlation function can be considered as a potentially valuable tool to diagnose exotic nuclear structures, such as the skin and halo.