arXiv 1808.040972018-08-29hep-phhep-ex

双夸克模型中的$ε_K$和$ε'/ε$

$ε_K$ and $ε'/ε$ in a diquark model

Chuan-Hung Chen, Takaaki Nomura

备注：: 44 pages, 10 figures, typos corrected, references added, and charged-Goldstone-boson effects included
DOI：: 10.1007/JHEP03(2019)009

摘要：

基于RBC-UKQCD合作的格点QCD和一个大的$N_c$对偶QCD的计算，得到的$ε'/ε$比标准模型（SM）的实验值小一个$2σ$以上，这表明了一个新的物理效应的必要性.为了补充$ε'/ε$的不足，我们研究了双夸克模型中带色标量的SM的扩张。除了纯双夸克盒图外，还发现文献中忽略的含有一个$W$ -玻色子和一个双夸克的盒图在$ΔS=2$过程中起着重要作用。在双夸克模型中，$K_L$和$K_S$的质量差远低于目前的数据，而K介子的间接CP破坏$ε_K$对新参数给出了严格的限制。在对$ε'/ε$的研究中，我们将其分为三种机制：树级图、QCD和电弱企鹅、色磁偶极子。以Kobayashi-Maskawa相作为唯一CP源，详细分析了三种机制的贡献，并得出结论：当满足$ε_K$的约束时，这些双夸克介导的效应可以单独地将$ε'/ε$增强为${\cal O}(10^{-3})$，这取决于自由参数的取值.

英文摘要：

Based on the calculations using the lattice QCD by RBC-UKQCD collaboration and a large $N_c$ dual QCD, the resulted $ε'/ε$, which is less than the experimental data by more than a $2σ$ in the standard model (SM), suggests the necessity of a new physics effect. In order to complement the insufficient $ε'/ε$, we study the extension of the SM with a colored scalar in a diquark model. In addition to the pure diquark box diagrams, it is found that the box diagrams with one $W$-boson and one diquark, ignored in the literature, play an important role in the $ΔS=2$ process. The mass difference between $K_L$ and $K_S$ in the diquark model is well below the current data, whereas the Kaon indirect CP violation $ε_K$ gives a strict constraint on the new parameters. Three mechanisms are classified in the study of $ε'/ε$, and they include: tree-level diagram, QCD and electroweak penguins, and chromomagnetic dipole. Taking the Kobayashi-Maskawa phase as the unique CP source, we analyze each contribution of the three mechanisms in detail and conclude that these diquark-mediated effects can singly enhance $ε'/ε$ to be of ${\cal O}(10^{-3})$, depending on the values of free parameters, when the bound from $ε_K$ is satisfied.

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英文摘要：

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