Isospin-symmetry breaking in superallowed Fermi β-decay due to isospin-nonconserving forces

• Published in: Physics letters. B Vol. 773; pp. 521 - 526
• Main Authors: Kaneko, K., Sun, Y., Mizusaki, T., Tazaki, S., Ghorui, S.K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.10.2017; Elsevier
• Subjects: Coulomb displacement energy; Isospin-nonconserving interaction; Isospin-symmetry breaking; Proton drip-line; Superallowed Fermi β-decay; Triplet displacement energy; Isospin-symmetry breaking; Coulomb displacement energy; Proton drip-line; Isospin-nonconserving interaction; Triplet displacement energy; Superallowed Fermi β-decay
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2017.08.056

We investigate isospin-symmetry breaking effects in the sd-shell region with large-scale shell-model calculations, aiming to understand the recent anomalies observed in superallowed Fermi β-decay. We begin with calculations of Coulomb displacement energies (CDE's) and triplet displacement energies (TDE's) by adding the T=1,J=0 isospin nonconserving (INC) interaction into the usual isospin-invariant Hamiltonian. It is found that CDE's and TDE's can be systematically described with high accuracy. A total number of 122 one- and two-proton separation energies are predicted accordingly, and locations of the proton drip-line and candidates for proton-emitters are thereby suggested. However, attempt to explain the anomalies in the superallowed Fermi β-decay fails because these well-fitted T=1,J=0 INC interactions are found no effects on the nuclear matrix elements. It is demonstrated that the observed large isospin-breaking correction in the 32Cl β-decay, the large isospin-mixing in the 31Cl β-decay, and the small isospin-mixing in the 23Al β-decay can be consistently understood by introducing additional T=1,J=2 INC interactions related to the s1/2 orbit.