Spin symmetry and its breaking in single-particle resonant states of 144Sm: A complex momentum representation study

In this paper, we investigate the spin symmetry (SS) and its breaking mechanism in single-particle resonant states of [Formula: see text]Sm using the complex momentum representation (CMR) method within the relativistic mean-field (RMF) framework. This work provides, for the first time, a systematic and quantitative analysis of how individual Woods–Saxon potential parameters-diffuseness a, radius R, and depth [Formula: see text]-govern SS breaking in resonant states of a spherical nucleus. By solving the Dirac equation with a Woods–Saxon potential, we systematically analyze the energy, width, and wave functions of spin partner states ([Formula: see text]). Key findings reveal that SS is well preserved in nuclear surface regions, with energy splittings near the continuum threshold being significantly smaller. Notably, the width splitting [Formula: see text] remains universally positive, driven by centrifugal barrier effects. We quantify the roles of potential parameters: (1) Diffuseness a reduces energy/width splittings and enhances wave function similarity; (2) Radius R exhibits opposite effects on bound (splitting[Formula: see text]) and resonant states (splitting[Formula: see text]); (3) Shallower wells ([Formula: see text]) suppress resonant-state energy splittings but amplify [Formula: see text]. Wave function splitting ([Formula: see text]) further distinguishes bound/resonant behaviors. These systematic parameter studies establish quantitative benchmarks for predicting symmetry evolution in exotic nuclei near drip lines, advancing beyond previous phenomenological approaches.