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arXiv 1803.07623hep-phhep-ex
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QCD中NNLO + NNLL '（增强）顶夸克对产生的恢复

Resummation for (boosted) top-quark pair production at NNLO+NNLL' in QCD

Michal Czakon, Andrea Ferroglia, David Heymes, Alexander Mitov, Ben D. Pecjak, Darren J. Scott, Xing Wang, Li Lin Yang

备注：
45 pages, 12 figures, 2 tables. Updated formatting and included a new appendix. Matches journal version
发表信息：
JHEP 1805 (2018) 149
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摘要：

我们构建了强子对撞机上顶夸克对微分分布的预测，结合了最先进的NNLO QCD计算和NNLL精度下的软胶子发射和小质量胶子发射的阈值胶子的双重再确认。这是第一次在微分水平上对具有非平凡色结构的过程在QCD中进行了全NNLO+NNLL'精度的数值计算。我们主要感兴趣的是M_{tt}和顶夸克p_T分布的稳定性在升压制度，固定的顺序计算可能会成为强烈依赖于动力学尺度的选择。数值和分析参数的帮助下，我们确认，最近提倡的一些作者的因式分解和重整化尺度的选择确实是最佳的。我们进一步推导出一组优化的运动学相关的尺度的匹配功能出现在图计算。我们对顶对不变质量的NNLO+NNLL'预测对因子分解标度的选择比固定阶预测显著更不敏感，即使在NNLO。值得注意的是，当使用最佳动态标度时，在全M_{tt}范围内，图解和固定阶计算几乎完全一致。对于顶夸克p_T分布，这里进行的重新计算影响较小，相反，我们发现，从NLO+NNLL'到NNLO+NNLL'的固定阶匹配升级是一个重要的影响，这是使用基于NLO的Monte Carlo事件发生器计算此分布时要记住的一点。

英文摘要：

We construct predictions for top quark pair differential distributions at hadron colliders that combine state-of-the-art NNLO QCD calculations with double resummation at NNLL' accuracy of threshold logarithms arising from soft gluon emissions and of small mass logarithms. This is the first time a resummed calculation at full NNLO+NNLL' accuracy in QCD for a process with non-trivial color structure has been completed at the differential level. Of main interest to us is the stability of the M_{tt} and top-quark p_T distributions in the boosted regime where fixed order calculations may become strongly dependent on the choice of dynamic scales. With the help of numeric and analytic arguments we confirm that the choice for the factorization and renormalization scales advocated recently by some of the authors is indeed optimal. We further derive a set of optimized kinematics-dependent scales for the matching functions which appear in the resummed calculations. Our NNLO+NNLL' prediction for the top-pair invariant mass is significantly less sensitive to the choice of factorization scale than the fixed order prediction, even at NNLO. Notably, the resummed and fixed order calculations are in nearly perfect agreement with each other in the full M_{tt} range when the optimal dynamic scale is used. For the top-quark p_T distribution the resummation performed here has less of an impact and instead we find that upgrading the matching with fixed-order from NLO+NNLL' to NNLO+NNLL' to be an important effect, a point to be kept in mind when using NLO-based Monte Carlo event generators to calculate this distribution.

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