Pairing effect on critical spin in chiral rotation

The critical spin I_c (or critical frequency ħω_c) represents the minimum spin (or rotational frequency) required for stable chiral solutions in nuclear systems. The effect of pairing on the critical spin has been examined for the particle-hole configuration π(1h_11/2)⊗ν(1h_11/2)⁻¹ with a triaxial deformation parameter of γ=30^∘ using the particle rotor model, which treats the total angular momentum as a good quantum number. Increasing pairing interaction keeps the critical spin I_c constant, but decreases the critical rotational frequency ħω_c. This is due to that the enhanced pairing interaction causes valence nucleons angular momenta to align preferentially along the medium axis, resulting in a larger effective collective moment of inertia and facilitating the emergence of chiral rotation at a lower frequency. However, even with an increase in pairing gap from 0.0 to 2.0MeV, the resulting increase in medium axis alignment is less than 1ħ, which is insufficient to change the value of the critical spin I_c. This study suggests that the critical spin remains robust against the influence of pairing interaction.