发表机构
Faculty of Physics, Ludwig-Maximilians-Universit\"at M\"unchen, Munich, Germany
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究利用Belle和Belle II数据搜索电弱企鹅B衰变，设定多个分支比上限，并在弱有效理论中重新诠释结果，发现数据偏好增强的矢量贡献。
AI 中文摘要
末态含中微子或$\tau$轻子的电弱企鹅$B$衰变是超越标准模型物理的灵敏探针。利用Belle的完整数据和Belle II Run 1数据，首次搜索$B^0 \to K^0_S\tau^+\tau^-$，将分支比的上限设为$\mathcal{B} < 8.3 \times 10^{-4}$；搜索$B^+ \to K^+\tau^+\tau^-$，得到$\mathcal{B} < 5.6 \times 10^{-4}$；其同位旋组合给出$\mathcal{B}(B \to K\tau^+\tau^-) < 5.4 \times 10^{-4}$，所有结果均在90%置信水平（CL$_s$）下获得。Belle II首次搜索包含式$B \to X_s\nu\bar\nu$衰变，设定$\mathcal{B} < 3.3 \times 10^{-4}$。最后，利用已发表的似然函数，在弱有效理论中重新诠释Belle II的$B^+ \to K^+\nu\bar\nu$结果。数据倾向于增强的矢量贡献，并略微支持非零的张量贡献。
英文摘要
Electroweak penguin $B$ decays with neutrinos or $τ$ leptons in the final state are sensitive probes of physics beyond the Standard Model. Using the full Belle and Run 1 Belle II datasets, the first search for $B^0 \to K^0_Sτ^+τ^-$ sets the upper limit on the branching fraction to $\mathcal{B} < 8.3 \times 10^{-4}$, the search for $B^+ \to K^+τ^+τ^-$ sets $\mathcal{B} < 5.6 \times 10^{-4}$, and their isospin combination gives $\mathcal{B}(B \to Kτ^+τ^-) < 5.4 \times 10^{-4}$, all at 90% confidence level (CL$_s$). The first search for inclusive $B \to X_sν\barν$ decays at Belle II sets $\mathcal{B} < 3.3 \times 10^{-4}$. Finally, the Belle II $B^+ \to K^+ν\barν$ result is reinterpreted in the Weak Effective Theory using its published likelihood. The data prefer an enhanced vector contribution and mildly favour a nonzero tensor contribution.
Comments6 pages, 4 figures. Contribution to the 43rd International Conference on High Energy Physics (ICHEP2026), 30 July - 5 August 2026, Natal, Brazil
