QCD企鹅算符对粲夸克CP破坏的标准模型上界的增强
Enhanced Standard Model bound on charm CP violation from QCD penguins
- Universität Siegen（锡根大学）
- CERN（欧洲核子研究中心）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文利用光锥求和规则计算QCD企鹅算符矩阵元，发现其可增强粲介子衰变中直接CP破坏的标准模型上界，缩小与实验的差距。
AI中文摘要：
我们在光锥求和规则（LCSR）框架内，利用π介子和K介子的光锥分布振幅，研究了QCD企鹅算符对单卡比博抑制的$D^0$衰变中直接CP破坏的影响。我们首次在$\alpha_s$领头阶，通过引入人工动量以避免非物理寄生割线的三点关联函数，确定了$D^0\to K^+K^-$和$D^0\to\pi^+\pi^-$衰变中QCD企鹅算符的强子矩阵元。我们还使用同一框架计算了流-流算符的矩阵元，并与先前的LCSR结果进行了比较。我们发现标量企鹅算符$Q_5$和$Q_6$的矩阵元可能被显著增强。我们识别出两种增强来源：夸克凝聚贡献，该贡献在树图阶即已出现，因此与求和规则中剩余的圈诱导项相比，被相对因子$16 \pi^2$所增强；以及来自这些算符的$\bar u u$分量的湮灭型贡献，该贡献通过扭度三的光锥分布振幅即已进入，且量级相当。虽然QCD企鹅算符对分支比的影响可忽略不计，但它们可以增强与直接CP破坏相关的“企鹅-树”振幅比的大小。然而，在我们框架的精度范围内，相关的强相位在很大程度上仍不受约束。假设最大相对强相位，我们发现相应的标准模型对粲夸克CP破坏贡献的上界相比仅基于流-流算符的估计可被增强，从而缩小了与实验测量之间的差距。
英文摘要：
We investigate the impact of QCD penguin operators on direct CP violation in singly Cabibbo-suppressed $D^0$ decays within the framework of light-cone sum rules (LCSR) using pion and kaon light-cone distribution amplitudes. We determine, for the first time, the hadronic matrix elements of the QCD penguin operators for $D^0\to K^+K^-$ and $D^0\toπ^+π^-$ at leading order in $α_s$, employing a three-point correlation function with an artificial momentum to avoid unphysical parasitic cuts. We also compute the matrix elements of the current-current operators using the same framework and compare them with previous LCSR results. We find that the scalar penguin operators $Q_5$ and $Q_6$ can have substantially enhanced matrix elements. We identify two sources of enhancement: quark-condensate contributions, which arise already at tree level and are therefore enhanced by a relative factor of $16 π^2$ compared to the remaining, loop-induced terms in the sum rule; and an annihilation-type contribution from the $\bar u u$ component of these operators, which enters already through twist-three light-cone distribution amplitudes and is of comparable magnitude. While the impact of QCD penguin operators on the branching ratios is negligible, they can enhance the magnitude of the ``penguin-to-tree'' amplitude ratios relevant for direct CP violation. The relevant strong phases, however, remain largely unconstrained within the accuracy of our framework. Assuming maximal relative strong phases, we find that the corresponding upper bound on the Standard Model contribution to charm CP violation can be enhanced compared to estimates based on the current-current operators alone, reducing the gap with the experimental measurement.
