A possible probe to neutron-skin thickness by fragment parallel momentum distribution in projectile fragmentation reactions

Neutron-skin thickness is a key parameter for a neutron-rich nucleus; however, it is difficult to determine. In the framework of the Lanzhou Quantum Molecular Dynamics (LQMD) model, a possible probe for the neutron-skin thickness (\(\delta _\text {np}\)) of neutron-rich \(^{48}\)Ca was studied in the 140A MeV \(^{48}\)Ca + \(^{9}\)Be projectile fragmentation reaction based on the parallel momentum distribution (\(p_\parallel \)) of the residual fragments. A Fermi-type density distribution was employed to initiate the neutron density distributions in the LQMD simulations. A combined Gaussian function with different width parameters for the left side (\(\Gamma _\text {L}\)) and the right side (\(\Gamma _\text {R}\)) in the distribution was used to describe the \(p_\parallel \) of the residual fragments. Taking neutron-rich sulfur isotopes as examples, \(\Gamma _\text {L}\) shows a sensitive correlation with \(\delta _\text {np}\) of \(^{48}\)Ca, and is proposed as a probe for determining the neutron skin thickness of the projectile nucleus.