标题： 自企鹅对$K \to 2 π$的贡献 显示英文标题

标题： The self-penguin contribution to $K \to 2 π$

摘要： 我们考虑来自非对角$s \ra d$夸克跃迁振幅的$K \rightarrow 2 \pi$衰变贡献。 首先，我们计算$s \rightarrow d$跃迁最重要的部分，即所谓的自-企鹅振幅$\sim G_F \alpha_s$，包括重顶夸克的情况。 其次，我们计算物理$K \rightarrow 2 \pi$过程中$s \rightarrow d$跃迁的矩阵元。 这一部分的分析是在手征夸克模型中进行的，其中夸克与赝标介子耦合。 发现$K \rightarrow 2\pi$的CP守恒自-企鹅贡献可以忽略不计。 对$\epsilon'/\epsilon$的贡献对夸克凝聚值$<\bar{q} q>$和组成夸克质量$M$的值是敏感的。 对于这些量的合理值，我们发现对$\epsilon'/\epsilon$的自胶子子贡献是胶子子贡献的 10-15%，并且符号相同。 考虑到胶子和电弱胶子子贡献之间的大抵消，这意味着我们的贡献与$\epsilon'/\epsilon$本身处于同一数量级。 显示英文摘要

摘要： We consider the contribution to $K \rightarrow 2 \pi$ decays from the non-diagonal $s \ra d$ quark transition amplitude. First, we calculate the most important part of the $s \rightarrow d$ transition, the so-called self-penguin amplitude $\sim G_F \alpha_s$, including the heavy top-quark case. Second, we calculate the matrix element of the $s \rightarrow d$ transition for the physical $K \rightarrow 2 \pi$ process. This part of the analysis is performed within the Chiral Quark Model where quarks are coupled to the pseudoscalar mesons. The CP-conserving self-penguin contribution to $K \rightarrow 2\pi$ is found to be negligible. The obtained contribution to $\epsilon'/\epsilon$ is sensitive to the values of the quark condensate $<\bar{q} q>$ and the constituent quark mass $M$. For reasonable values of these quantities we find that the self-penguin contribution to $\epsilon'/\epsilon$ is 10-15% of the gluonic penguin contribution and has the same sign. Given the large cancellation between gluonic and electroweak penguin contributions, this means that our contribution is of the same order of magnitude as $\epsilon'/\epsilon$ itself.