Isobaric multiplet mass equation in the $A=31$ $T = 3/2$ quartets
Abstract
The observed mass excesses of analog nuclear states with the same mass number and isospin can be used to test the isobaric multiplet mass equation (IMME), which has, in most cases, been validated to a high degree of precision. A recent measurement [Kankainen et al., Phys. Rev. C 93 041304(R) (2016)] of the ground-state mass of Cl led to a substantial breakdown of the IMME for the lowest quartet. The second-lowest quartet is not complete, due to uncertainties associated with the identity of the S member state. Using a fast Cl beam implanted into a plastic scintillator and a high-purity Ge -ray detection array, rays from the ClS sequence were measured. Shell-model calculations using USDB and the recently-developed USDE interactions were performed for comparison. Isospin mixing between the S isobaric analog state (IAS) at 6279.0(6) keV and a nearby state at 6390.2(7) keV was observed. The second state in S was observed at keV. Isospin mixing in S does not by itself explain the IMME breakdown in the lowest quartet, but it likely points to similar isospin mixing in the mirror nucleus P, which would result in a perturbation of the P IAS energy. USDB and USDE calculations both predict candidate P states responsible for the mixing in the energy region slightly above keV. The second quartet has been completed thanks to the identification of the second S state, and the IMME is validated in this quartet.
Cite
@article{arxiv.1607.00690,
title = {Isobaric multiplet mass equation in the $A=31$ $T = 3/2$ quartets},
author = {M. B. Bennett and C. Wrede and B. A. Brown and S. N. Liddick and D. Pérez-Loureiro and D. W. Bardayan and A. A. Chen and K. A. Chipps and C. Fry and B. E. Glassman and C. Langer and N. R. Larson and E. I. McNeice and Z. Meisel and W. Ong and P. D. O'Malley and S. D. Pain and C. J. Prokop and S. B. Schwartz and S. Suchyta and P. Thompson and M. Walters and X. Xu},
journal= {arXiv preprint arXiv:1607.00690},
year = {2016}
}