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$D \to KK$衰变中的CP破坏：三重子和六重子双夸克的比较分析

CP Violation in $D \to KK$ Decays: A Comparative Analysis of Triplet and Sextet Diquarks

Universidad de Guanajuato（瓜纳华托大学）；Zewail City of Science and Technology（齐维尔科学与技术城）；Universidad de los Andes（洛斯安第斯大学）

David Delepine, Shaaban Khalil, Carlos A. Ramirez

备注：
19 pages, 2 figures
发表信息：
Phys. Rev. D 114,035037 (2026)
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AI总结：

本文研究了$D \to KK$衰变中色六重双夸克对CP破坏的贡献，发现其能解释观测到的CP不对称性偏离。

摘要：

最近CMS合作组对$D^0 \rightarrow K_S^0 K_S^0$衰变的CP不对称性的测量结果为$A_{CP}(K_S^0 K_S^0) = (6.2 \pm 3.0 \pm 0.2 \pm 0.8)\%$，而LHCb的结果为$A_{CP}(D^0 \to K_S^0 K_S^0) = (1.86 \pm 1.04 \pm 0.41)\%$，这些结果表明可能偏离标准模型（SM）的预期，标准模型预测的不对称性低于百分比水平。这种单倍Cabibbo抑制衰变特别敏感于新物理，因为在精确U旋对称性极限下，主导振幅消失，过程由W交换拓扑结构主导。我们研究了标量双夸克对这种衰变的贡献，比较了色六重和色三重表示。我们发现色六重双夸克，其色结构对称$(C_1^{\mathrm{NP}} = C_2^{\mathrm{NP}})$，避免了色抑制，可以在双夸克质量约为1 TeV时生成CP不对称性在$0.5\%$--$1.5\%$范围内。相反，色三重贡献由于其反对称色结构的破坏性干涉而被强烈抑制。我们进一步表明，六重耦合中的味层次结构，具有$λ_{ud} > λ_{us}$，可以同时解释观测到的偏离U旋总规则在$D^0 \to K^+ K^-$和$D^0 \to π^+ π^-$以及$D^0 \to K_S^0 K_S^0$中测量的CP不对称性。这些结果将色六重标量双夸克识别为解释charm衰变中增强的CP破坏的可行候选者。

英文摘要：

Recent measurements of the CP asymmetry in the decay $D^0 \rightarrow K_S^0 K_S^0$ by the CMS collaboration, $A_{CP}(K_S^0 K_S^0) = (6.2 \pm 3.0 \pm 0.2 \pm 0.8)\%$, and by LHCb, $A_{CP}(D^0 \to K_S^0 K_S^0) = (1.86 \pm 1.04 \pm 0.41)\%$, suggest possible deviations from Standard Model (SM) expectations, which predict asymmetries below the percent level. This singly Cabibbo-suppressed decay is particularly sensitive to new physics, as the leading amplitudes vanish in the exact U-spin symmetry limit and the process is dominated by W-exchange topologies. We investigate scalar diquark contributions to this decay, comparing color-sextet and color-triplet representations. We find that the color-sextet diquark, characterized by a symmetric color structure $(C_1^{\mathrm{NP}} = C_2^{\mathrm{NP}})$, avoids color suppression and can generate CP asymmetries in the range $0.5\%$--$1.5\%$ for a diquark mass of order 1~TeV. In contrast, the color-triplet contribution is strongly suppressed due to destructive interference from its antisymmetric color structure. We further show that a flavor hierarchy in the sextet couplings, with $λ_{ud} > λ_{us}$, can simultaneously account for the observed deviation from the U-spin sum rule in $D^0 \to K^+ K^-$ and $D^0 \to π^+ π^-$ and the measured CP asymmetry in $D^0 \to K_S^0 K_S^0$. These results identify color-sextet scalar diquarks as viable candidates for explaining enhanced CP violation in charm decays.

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