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

Abstract

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 beta-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 beta-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 beta-decay, the large isospin-mixing in the 31Cl beta-decay, and the small isospin-mixing in the 23Al beta-decay can be consistently understood by introducing additional T=1,J=2 INC interactions related to the s1/2 orbit.

arXiv comment7 pages, 3 figures, accepted in Phys. Lett. B

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• Effects of Coulomb and isospin symmetry breaking interactions on neutron-skin thickness
• Precision calculation of isospin-symmetry-breaking corrections to T=1/2 mirror decays using multi-reference charge-dependent density functional theory
• Exploring isospin-nonconserving effects in the upper $fp$ shell with new mass measurements
• Charge-dependent nucleon-nucleon interaction at N${}^3$LO in nuclear lattice effective field theory
• Gamow shell model calculations for the Thomas-Ehrman shift in new isotopes 21Al
• Isoscalar, isovector and orbital contributions in $M1$ transitions from analogous $M1$ and Gamow-Teller transitions in $T=\frac{1}{2}$ mirror nuclei
• Shell model study of isobaric analog states for $T_z=\pm 2$ nuclei using isospin non-conserving interactions
• Charge symmetry breaking effects of $\omega$-${\rho }^0$ mixing in relativistic mean-field model