通过半轻衰变B→D^(* )ℓν_ℓ排他性确定|V_{cb}|

中文摘要 AI 辅助

我们通过半轻衰变B→D^(* )ℓν_ℓ开展CKM矩阵元|V_{cb}|的排他性确定工作。本分析结合了最新的Belle II测量结果、小强子反冲下B→D^(* )形状因子的格点QCD计算更新结果，以及包含次领头阶QCD修正和多个幂次压低贡献的关联大反冲SCET求和规则预测。我们考虑了三组输入集逐步扩大的拟合场景，发现纳入大反冲求和规则约束可大幅降低形状因子的不确定性。通过完整全局拟合，我们得到|V_{cb}|=(39.18±0.47)×10^{-3}。利用结合格点QCD与LCSR的拟合，我们预测R(D)=0.3069±0.0080、R(D^(*))=0.2548±0.0043，并给出缪子和陶子道在动量转移及角变量下的微分衰变分布。对R(D)与R(D^(*))的个体及关联预测与实验平均值的对比显示存在持续的张力，特别是我们的理论68%置信区间与实验平均值几乎无重叠。不确定性传播过程中保留了所有拟合参数间的关联。因此，本结果为轻子味普适性检验提供了更新的标准模型基准。改进的格点QCD计算、求和规则预测及Belle II测量，对于确定剩余偏差源于理论系统不确定性还是超出标准模型的新物理至关重要。

英文摘要

We present an updated exclusive determination of the CKM matrix element \(|V_{cb}|\) from the semileptonic decays \(B\to D^{(*)}\ell\barν_{\ell}\). Our analysis combines the latest Belle II measurements, updated lattice-QCD calculations of the \(B\to D^{(*)}\) form factors at small hadronic recoil, and correlated large-recoil SCET sum-rule predictions incorporating next-to-leading-order QCD corrections and several power-suppressed contributions. We consider three fit scenarios with progressively enlarged input sets and find that the inclusion of the large-recoil sum-rule constraints substantially reduces the form-factor uncertainties. From the full global fit, we obtain\(|V_{cb}|=(39.18 \pm0.47)\times10^{-3}\). Using the combined lattice-QCD and LCSR fit, we predict \(R(D)=0.3069\pm0.0080,\qquad R(D^*)=0.2548\pm0.0043\), and provide differential decay distributions in the momentum transfer and angular variables for both the muon and tau channels. Comparisons of the individual and correlated predictions for \(R(D)\) and \(R(D^*)\) with the experimental averages reveal a persistent tension. In particular, our theoretical 68\% confidence region shows little overlap with the experimental average. All correlations among the fitted parameters are retained in the uncertainty propagation. Our results therefore provide updated Standard Model benchmarks for tests of lepton-flavor universality. Improved lattice-QCD calculations, sum-rule predictions, and Belle II measurements will be essential for determining whether the remaining discrepancies originate from theoretical systematic uncertainties or from physics beyond the Standard Model.

发表机构

• Chongqing University of Science and Technology（重庆科技大学）
• Nankai University（南开大学）
• Army Medical University（陆军军医大学）

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