发表机构
School of Physics, Beihang University; School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University; Center for High Energy Physics, Peking University（北京航空航天大学物理学院; 北京大学物理学院与核物理及技术国家重点实验室; 北京大学高能物理中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
提出自旋密度矩阵框架，利用b夸克与W玻色子的自旋关联探测顶夸克对产生中的反常Wtb耦合，在HL-LHC上显著提升对V_R和g_L的敏感性。
AI 中文摘要
我们提出一个自旋密度矩阵框架，通过利用b夸克和W玻色子的极化及其自旋关联来探测顶夸克对产生中的反常Wtb相互作用。b夸克的自旋通过碎裂后半轻子Λ_b衰变中的角分布进行分析，而轻子W衰变则作为W极化分析器。我们在存在反常Wtb耦合的情况下推导出bW自旋密度矩阵，并表明其极化和自旋关联参数对这些耦合提供线性敏感性。我们构建了与这些参数相关的实验可观测的角观测量，并评估其统计敏感性。对于质心能量为√s=14 TeV、积分亮度为3000 fb^{-1}的HL-LHC，所提出的方法对大多数反常Wtb耦合给出了改进的约束，其中对V_R的敏感性提高了8倍，对g_L的敏感性提高了约6倍。
英文摘要
We propose a spin-density-matrix framework for probing anomalous $Wtb$ interactions in top-quark pair production by exploiting the polarizations of the $b$ quark and the $W$ boson and their spin correlations. The $b$-quark spin is analyzed through angular distributions in semileptonic $Λ_b$ decay following fragmentation, while the leptonic $W$ decay serves as a $W$-polarization analyzer. We derive the $bW$ spin density matrix in the presence of anomalous $Wtb$ couplings and show that its polarization and spin-correlation parameters provide linear sensitivity to these couplings. We construct experimentally accessible angular observables associated with these parameters and evaluate their statistical sensitivities. For the HL-LHC at $\sqrt{s}=14~ \mathrm{TeV}$ with an integrated luminosity of $3000~ \mathrm{fb}^{-1}$, the proposed method yields improved constraints on most anomalous $W t b$ couplings, with the sensitivity to $V_R$ enhanced by a factor of 8 and that to $g_L$ by a factor of about 6.
Comments33 pages, 4 tables, 3 figures
