$t\bar{t}$ 自旋关联：从toponium产生场景到超越标准微扰基线的非相对论重求和
$t\bar{t}$ spin correlations from toponium production scenarios to non-relativistic resummation beyond the standard perturbative baseline
- Department of Physics and Astronomy, The University of Kansas（堪萨斯大学物理与天文学系）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文比较toponium产生与非相对论QCD重求和效应对$t\bar{t}$自旋关联的影响，发现自旋关联显著增强，重求和改善数据符合度，并证明有效分离$t\bar{t}$额外事件可行。
AI中文摘要：
本文比较了在13 TeV质子-质子碰撞中假设toponium束缚态形成的理论模型所产生的$t\bar{t}$自旋关联，与通过格林函数形式化的非相对论QCD重求和效应（超越无束缚态的微扰$t\bar{t}$基线，但可能解释ATLAS和CMS合作组最近观察到的、尚待解释的$t\bar{t}$质量谱中额外事件产额）的预测。Toponium产生包含两种场景：一种简化的有效场论（EFT），具有$\eta_t\rightarrow t\bar{t}$衰变；另一种额外模型，包含标量和矢量toponium态，具有$\eta_t\rightarrow HZ$和$J_t\rightarrow ZW^+W^-$衰变。实验测量的$t\bar{t}$系统数据也被加入比较。拟合的对角自旋关联矩阵元$C_{kk}$、$C_{rr}$、$C_{nn}$相对于微扰NLO基线，在toponium $t\bar{t}$衰变中显示出200%至2330%的相对增加。重求和效应的相对贡献范围为0.6%至10.4%，其与微扰基线的组合改善了对数据分布的符合度，$\chi^2/N_\mathrm{dof}$值降低了约4.5%至60.0%。重求和效应的等效拟合截面$\sigma_{res}$范围为7.3至9.1 pb，与LHC实验报告的额外产额一致。$\sigma_{res}>50$ pb的范围在95%置信水平下被排除。一个在探测器层面运行的分类器实现了0.91的ROC曲线面积，导致toponium信号对背景的显著性超过55。这些结果表明，从背景中有效分离观察到的$t\bar{t}$额外事件是可行的，并且通过自旋关联测量的表征将揭示它们与toponium产生或超越微扰基线的非相对论效应的一致性。
英文摘要：
$t\bar{t}$ spin correlations originating from theoretical models assuming on one side toponium bound state formation in proton-proton collisions at 13 TeV are compared against predictions from non-relativistic QCD ressumation effects via Green's function formalism that go beyond the perturbative $t\bar{t}$ baseline with no bound state but could justify extra yield of events in the $t\bar{t}$ mass spectrum recently observed by ATLAS and CMS Collaborations, still awaiting an explanation. Toponium production comprises two scenarios, a simplified Effective Field Theory (EFT) with $η_t\rightarrow t\bar{t}$ decays and an additional model with scalar and vector toponium states with $η_t\rightarrow HZ$ and $J_t\rightarrow ZW^+W^-$ decays. Experimental measurements on $t\bar{t}$ system are added to the comparisons. Fitted diagonal spin correlation $C_{kk}$, $C_{rr}$, $C_{nn}$ matrix terms show a relative increase in value ranging from 200%-2330% for toponium $t\bar{t}$ decays with respect the perturbative NLO baseline. Relative contribution from resummation effect ranges from 0.6% to 10.4% and its combination with perturbative baseline improves agreement with Data distributions, with $χ^2/N_\mathrm{dof}$ value reduced by $\sim$4.5%-60.0% . Equivalent fitted cross-section for resummation effect $σ_{res}$, ranges from 7.3 to 9.1 pb in consistency with excess yield reported by LHC experiments. $σ_{res}$ $>$ 50 pb range is excluded at 95% C.L. A classifier performing at detector level achieves a ROC curve area of $0.91$ leading to toponium signal to background significances over 55. These results indicate that efficient isolation of observed $t\bar{t}$ excess events from background is feasible and a characterisation via spin correlation measurements would reveal their consistency with either toponium production or non-relativistic effects beyond the perturbative baseline.
