Mass Measurement of Upper <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>f</mml:mi><mml:mi>p</mml:mi></mml:math>-Shell <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mi>Z</mml:mi><mml:mo>−</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mi>Z</mml:mi><mml:mo>−</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> Nuclei and the Importance of Three-Nucleon Force along the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mi>Z</mml:mi></mml:math> Line
M. Wang, Y. H. Zhang, Xianming Zhou, Xiao-Hong Zhou, X. Xu, M. L. Liu, J. G. Li, Y. Niu, W. J. Huang, Qiong Yuan, S. Zhang, F. R. Xu, Yu. A. Litvinov, K. Blaum, Z. Meisel, R. F. Casten, R. B. Cakirli, R. J. Chen, Huiyong Deng, Chuancheng Fu, Wenwei Ge, H.F. Li, Ting Liao, S. Litvinov, P. Shuai, J. Y. Shi, Y. N. Song, M. Z. Sun, Quan Wang, Y. M. Xing, X. Xu, X. L. Yan, Jiancheng Yang, Youjin Yuan, Q. Zeng, M. Zhang
Abstract
Using a novel method of isochronous mass spectrometry, the masses of $^{62}\mathrm{Ge}$, $^{64}\mathrm{As}$, $^{66}\mathrm{Se}$, and $^{70}\mathrm{Kr}$ are measured for the first time, and the masses of $^{58}\mathrm{Zn}$, $^{61}\mathrm{Ga}$, $^{63}\mathrm{Ge}$, $^{65}\mathrm{As}$, $^{67}\mathrm{Se}$, $^{71}\mathrm{Kr}$, and $^{75}\mathrm{Sr}$ are redetermined with improved accuracy. The new masses allow us to derive residual proton-neutron interactions ($\ensuremath{\delta}{V}_{pn}$) in the $N=Z$ nuclei, which are found to decrease (increase) with increasing mass $A$ for even-even (odd-odd) nuclei beyond $Z=28$. This bifurcation of $\ensuremath{\delta}{V}_{pn}$ cannot be reproduced by the available mass models, nor is it consistent with expectations of a pseudo-SU(4) symmetry restoration in the $fp$ shell. We performed ab initio calculations with a chiral three-nucleon force (3NF) included, which indicate the enhancement of the $T=1$ $pn$ pairing over the $T=0$ $pn$ pairing in this mass region, leading to the opposite evolving trends of $\ensuremath{\delta}{V}_{pn}$ in even-even and odd-odd nuclei.