AI 中文总结
本研究在SMEFT框架下，利用OOT分析FCC-ee不同能量阶段Z/γ介导的重味FCNC过程，推导SMEFT算子约束，揭示偶极贡献干涉模式，明确其探索味违反现象的潜力与互补性。
AI 中文摘要
标准模型（SM）的味结构仍是粒子物理学中最引人注目的问题之一，第三代粒子因质量显著更大、测量精度相对较低而尤为引人关注。这些特性使得第三代味转变在寻找超出SM的新物理背景下格外受关注。本研究在SM有效场论（SMEFT）框架内，利用偶极算子和希格斯流算子，研究由中性规范玻色子（Z/γ）介导的第三代与前两代之间的味违反转变。我们采用最优可观测量技术（OOT），在即将到来的未来环形对撞机的e+e-模式（FCC-ee）的不同质心系能量下确定最优灵敏度；还从低能味违反可观测量和重费米子衰变道推导了对相关SMEFT算子的互补约束。我们的分析进一步揭示了偶极贡献之间的特征干涉模式，该模式取决于潜在的味转变，且在Z极点和更高能的FCC-ee阶段表现出不同行为。FCC-ee为电弱标度下的味违反相互作用提供了互补且直接的探针，其预测显示对若干相互作用的灵敏度有所提升，对其他若干相互作用则与现有味约束的灵敏度相当。这凸显了对FCC-ee不同能量阶段进行系统评估的重要性，该评估能全面展现其探索味违反现象的潜力及其与低能味实验的互补性。
英文摘要
The flavor structure of the Standard Model (SM) remains one of the most compelling questions in particle physics, with the third generation being particularly intriguing due to its significantly larger masses and comparatively less precisely measured properties. These features make third-generation flavor transitions particularly interesting in context of search for physics beyond the SM. In this work, we investigate flavor-violating transitions between the third and the first two generations, mediated by the neutral gauge bosons ($Z/γ$), within the framework of the SM Effective Field Theory (SMEFT), using dipole and Higgs-current operators. We determine the optimal sensitivities using the optimal observable technique (OOT) at different center-of-mass energies of the upcoming Future Circular Collider in the $e^+e^-$ mode (FCC-ee). We further derive complementary constraints on the relevant SMEFT operators from low-energy flavor-violating observables and heavy fermion decay channels. Our analysis also reveals characteristic interference patterns among the dipole contributions, which depend on the underlying flavor transition and exhibit distinct behavior between the $Z$ pole and higher-energy FCC-ee stages. The FCC-ee provides a complementary and direct probe of flavor-violating interactions at the electroweak scale, with the projections showing improved sensitivity for several interactions and comparable sensitivity to existing flavor constraints for several others. This highlights the importance of a systematic assessment across the different FCC-ee energy stages, which provides a comprehensive picture of its potential to explore flavor-violating phenomena and its complementarity with low-energy flavor experiments.
Comments44 pages, 9 figures, and 13 tables
