蒙特卡洛事例产生器的顶夸克质量校准——更新
Top Quark Mass Calibration for Monte Carlo Event Generators -- An Update
AI总结：
本文更新面向 MC 事例产生器的顶夸克质量校准框架，引入多种形状变量与间隙减除方案，揭示 PYTHIA、HERWIG 和 SHERPA 的共振位置差异源于强子化建模。
摘要：
我们推广并更新了此前用于蒙特卡洛（MC）事例产生器的顶夸克质量校准框架。该框架基于在共振区中针对 boosted $t\bar t$ 产生的 $e^+e^-$ 强子层级 2-jettiness $τ_2$ 分布，曾用于把 PYTHIA 8.205 的顶质量参数 $m_t^{\rm MC}$ 与 MSR 质量 $m_t^{\rm MSR}(R)$ 及极点质量 $m_t^{\rm pole}$ 联系起来。当前最精确的直接顶夸克质量测量具体确定的是 $m_t^{\rm MC}$。更新后的框架加入了形状变量喷注质量之和 $τ_s$ 与修正喷注质量 $τ_m$，并处理另外两种间隙减除方案，以消除与大角度软辐射相关的 $\mathcal{O}(Λ_{\rm QCD})$ renormalon。这些推广要求实现更通用的形状函数拟合程序，并计入某类 $(m_t/Q)^2$ 幂次修正，以获得与间隙方案和观测量无关的结果。理论描述采用次-次-对数阶（N$^2$LL）的 boosted 重夸克有效理论（bHQET），并与 N$^2$LL 的软共线有效理论（SCET）和次领头阶（NLO）的完整 QCD 匹配，同时包含主要的顶夸克宽度效应。此外，软件框架已现代化，以使用标准文件和事例记录格式。我们通过将新框架应用于 PYTHIA 8.205、HERWIG 7.2 和 SHERPA 2.2.11 来更新顶夸克质量校准结果。尽管对于相同的顶质量参数 $m_t^{\rm MC}$ 值，三个产生器给出的强子层级共振位置差异显著，但校准表明这些差异来源于强子化建模。事实上，我们发现对于这三个产生器，$m_t^{\rm MC}$ 与 $m_t^{\rm MSR}(1\\,\mbox{GeV})$ 在 200 MeV 内一致，而与极点质量相差 350 至 600 MeV。
英文摘要：
We generalize and update our former top quark mass calibration framework for Monte Carlo (MC) event generators based on the $e^+e^-$ hadron-level 2-jettiness $τ_2$ distribution in the resonance region for boosted $t\bar t$ production, that was used to relate the PYTHIA 8.205 top mass parameter $m_t^{\rm MC}$ to the MSR mass $m_t^{\rm MSR}(R)$ and the pole mass $m_t^{\rm pole}$. The current most precise direct top mass measurements specifically determine $m_t^{\rm MC}$. The updated framework includes the addition of the shape variables sum of jet masses $τ_s$ and modified jet mass $τ_m$, and the treatment of two more gap subtraction schemes to remove the ${\cal O}(Λ_{\rm QCD})$ renormalon related to large-angle soft radiation. These generalizations entail implementing a more versatile shape-function fit procedure and accounting for a certain type of $(m_t/Q)^2$ power corrections to achieve gap-scheme and observable independent results. The theoretical description employs boosted heavy-quark effective theory (bHQET) at next-to-next-to-logarithmic order (N$^2$LL), matched to soft-collinear effective theory (SCET) at N$^2$LL and full QCD at next-to-leading order (NLO), and includes the dominant top width effects. Furthermore, the software framework has been modernized to use standard file and event record formats. We update the top mass calibration results by applying the new framework to PYTHIA 8.205, HERWIG 7.2 and SHERPA 2.2.11. Even though the hadron-level resonance positions produced by the three generators differ significantly for the same top mass parameter $m_t^{\rm MC}$ value, the calibration shows that these differences arise from the hadronization modeling. Indeed, we find that $m_t^{\rm MC}$ agrees with $m_t^{\rm MSR}(1\,\mbox{GeV})$ within $200$ MeV for the three generators and differs from the pole mass by $350$ to $600$ MeV.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
