Charge-symmetry breaking forces and isospin mixing in 8 Be
Charge-symmetry breaking forces and isospin mixing in 8 Be
复制标题
8 Be 中的电荷对称破坏力和同位旋混合
DOI：
10.1103/physrevc.88.044333
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发表时间：
2013
影响因子：
3.1
通讯作者：
G. Miller
中科院分区：
文献类型：
--
作者：
R. Wiringa;S. Pastore;S. Pieper;G. Miller
本文报道了在16—19 MeV激发下8Be中2+、1+和3+ T=0,1对态的同位旋混合（IM）矩阵元的格林函数蒙特卡罗计算。利用现实的Argonne v18 （AV18）二核子势和Illinois-7三核子势生成核波函数。评估了AV18电位的全电磁相互作用和强III类电荷对称破缺（CSB）分量的贡献。我们还研究了基于ro -混合的两个理论上更完整的CSB势，调谐到与AV18相同的中子-中子散射长度。计算了这些不同的CSB势对3H-3He、7Li-7Be和8Li-8B等向能差的贡献，得到了与实验结果较为一致的结果。最后，对于8Be IM计算，我们添加了来自单光子、单介子和一交换以及混合的小类IV CSB项。三种CSB模型的期望值在等矢量能量差中相差高达20%，但在IM矩阵元素中仅相差10%或更少。对于2+双重态，总矩阵元素给出了-145 keV实验IM值的85- 90%，其中约三分之二来自库仑相互作用。我们还报告了IM矩阵元素在3mev激发下的第一个2+状态，这是β衰变标准模型各种测试的最终状态。
We report Green's function Monte Carlo calculations of isospin-mixing (IM) matrix elements for the 2+, 1+, and 3+ T=0,1 pairs of states at 16--19 MeV excitation in 8Be. The realistic Argonne v18 (AV18) two-nucleon and Illinois-7 three-nucleon potentials are used to generate the nuclear wave functions. Contributions from the full electromagnetic interaction and strong class III charge-symmetry-breaking (CSB) components of the AV18 potential are evaluated. We also examine two theoretically more complete CSB potentials based on rho-omega mixing, tuned to give the same neutron-neutron scattering length as AV18. The contribution of these different CSB potentials to the 3H-3He, 7Li-7Be, and 8Li-8B isovector energy differences is evaluated and reasonable agreement with experiment is obtained. Finally, for the 8Be IM calculation we add the small class IV CSB terms coming from one-photon, one-pion, and one-rho exchange, as well as rho-omega mixing. The expectation values of the three CSB models vary by up to 20% in the isovector energy differences, but only by 10% or less in the IM matrix element. The total matrix element gives 85--90% of the experimental IM value of -145 keV for the 2+ doublet, with about two thirds coming from the Coulomb interaction. We also report the IM matrix element to the first 2+ state at 3 MeV excitation, which is the final state for various tests of the Standard Model for beta-decay.