Further explorations of Skyrme–Hartree–Fock–Bogoliubov mass formulas; VI: Weakened pairing

All our previous mass models suffered from the defect of excessively strong pairing, as a result of the pairing parameters being fitted freely to the mass data. Starting from model HFB-9, and maintaining the condition that neutron matter be fitted, we construct four new models in which the pairing is constrained in such a way as to bring down the spectral pairing gap to be close to the experimental even–odd differences. These models differ in the treatment of the pairing, with two making use of Bulgac–Yu regularization. Our best new model, HFB-13, outperforms HFB-9.