arXiv 1003.58272010-03hep-ph

重整化群改进的强子对撞机顶夸克对产生的预测

Renormalization-Group Improved Predictions for Top-Quark Pair Production at Hadron Colliders

Valentin Ahrens, Andrea Ferroglia, Matthias Neubert, Ben D. Pecjak, Li Lin Yang

备注：: 61 pages, 18 figures, version to appear in JHEP
发表信息：: JHEP 1009:097,2010
DOI：: 10.1007/JHEP09(2010)097

摘要：

精确预测现象学上有趣的观测量，如强子对撞机上顶夸克对产生中的t-tbar不变质量分布和前后不对称性，需要控制微扰QCD中的微分截面。本文改进了已有的在不变质量和散射角下的双微分截面的计算方法，利用软共线有效理论中的技巧，对当顶夸克对的不变质量M接近部分子质心能量时变大的阈值粒子进行了NNLL重新计算。我们还导出了一个近似公式的微分截面在NNLO在固定阶微扰理论，它完全确定的系数乘以奇异正分布。然后，我们匹配我们的结果在阈值区域与固定阶微扰理论在非线性光学的精确结果，并进行数值分析的不变质量分布，总截面，和向前向后的不对称性。我们认为，这些是目前最准确的预测这些观测。利用MSTW 2008 NNLO部分子分布函数（PDF），α_s（M_Z）=0.117，m_t=173.1 GeV，我们得到了Tevatron和LHC的包容产生截面的σ_{Tevatron} =（6.30 +-0.19 +0.31-0.23）pb，σ_{LHC} =（149 +-7 +-8）pb，其中第一个误差由标度变化引起，第二个误差反映PDF的不确定性。

英文摘要：

Precision predictions for phenomenologically interesting observables such as the t-tbar invariant mass distribution and forward-backward asymmetry in top-quark pair production at hadron colliders require control over the differential cross section in perturbative QCD. In this paper we improve existing calculations of the doubly differential cross section in the invariant mass and scattering angle by using techniques from soft-collinear effective theory to perform an NNLL resummation of threshold logarithms, which become large when the invariant mass M of the top-quark pair approaches the partonic center-of-mass energy. We also derive an approximate formula for the differential cross section at NNLO in fixed-order perturbation theory, which completely determines the coefficients multiplying the singular plus distributions. We then match our results in the threshold region with the exact results at NLO in fixed-order perturbation theory, and perform a numerical analysis of the invariant mass distribution, the total cross section, and the forward-backward asymmetry. We argue that these are the most accurate predictions available for these observables at present. Using MSTW2008NNLO parton distribution functions (PDFs) along with α_s(M_Z)=0.117 and m_t=173.1 GeV, we obtain for the inclusive production cross sections at the Tevatron and LHC the values σ_{Tevatron} = (6.30 +-0.19 +0.31-0.23) pb and σ_{LHC} = (149 +- 7 +- 8) pb, where the first error results from scale variations while the second reflects PDF uncertainties.

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英文摘要：

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