$Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si

Y. M. Xing; Y. F. Luo; Y. H. Zhang; M. Wang; X. H. Zhou; J. G. Li; K. H. Li; Q. Yuan; Y. F. Niu; J. Y. Guo; J. C. Pei; F. R. Xu; G. de Angelis; Yu. A. Litvinov; K. Blaum; I. Tanihata; T. Yamaguchi; Y. Yu; X. Zhou; H. S. Xu; Z. Y. Chen; R. J. Chen; H. Y. Deng; C. Y. Fu; W. W. Ge; W. J. Huang; H. Y. Jiao; H. F. Li; T. Liao; J. Y. Shi; M. Si; M. Z. Sun; P. Shuai; X. L. Tu; Q. Wang; X. Xu; X. L. Yan; Y. J. Yuan; M. Zhang

arXiv · 2503.01380

$Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si

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Abstract

Using the $B\rho$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus $^{22}$Si. We confirm that $^{22}$Si is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)$ keV, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that $^{22}$Si exhibits a doubly-magic character similar to its mirror partner $^{22}$O, and that the mirror energy difference of $^{22}$Si-$^{22}$O deviates from the predictions assuming mirror symmetry. Gamow shell-model calculations reveal that the average occupations of valence protons in $^{22}$Si are nearly identical to those of valence neutrons in $^{22}$O, supporting the $Z=14$ magicity in $^{22}$Si. The observed mirror-symmetry breaking is attributed to the extended proton distribution in $^{22}$Si arising from a small contribution of the unbound $\pi2s_{1/2}$ orbital.

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Y. M. Xing, Y. F. Luo, Y. H. Zhang, M. Wang, X. H. Zhou, J. G. Li, K. H. Li, Q. Yuan, Y. F. Niu, J. Y. Guo, J. C. Pei, F. R. Xu, G. de Angelis, Yu. A. Litvinov, K. Blaum, I. Tanihata, T. Yamaguchi, Y. Yu, X. Zhou, H. S. Xu, Z. Y. Chen, R. J. Chen, H. Y. Deng, C. Y. Fu, W. W. Ge, W. J. Huang, H. Y. Jiao, H. F. Li, T. Liao, J. Y. Shi, M. Si, M. Z. Sun, P. Shuai, X. L. Tu, Q. Wang, X. Xu, X. L. Yan, Y. J. Yuan, M. Zhang. 2025-03-03. $Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si. https://arxiv.org/abs/2503.01380

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