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arXiv 0901.3780hep-ph
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有效的事件预测:因子化、恢复和有间隙的角度分布

Effective Predictions of Event Shapes: Factorized, Resummed, and Gapped Angularity Distributions

Andrew Hornig, Christopher Lee, Grigory Ovanesyan

摘要:

利用软共线有效理论(SCET),它提供了一个统一的框架,因式分解,remmation的,并在硬散射QCD截面中纳入通用的非微扰函数,我们提出了一个新的预测e+e-湮灭的角度分布。角τ_a是事件形状的无限类,其在其对最终状态中的射流的子结构的敏感性方面变化,由连续参数α <2控制。我们计算了强耦合α_s中所有α <1到一阶的角度分布,并将这些分布中的大值求和到次领先对数(NLL)精度。首次给出了次领先级(NLO)O(alpha_s)部分子喷流和角分布因子分解定理中的软函数的表达式。我们采用了一个模型的非微扰软函数的间隙参数,取消了部分子软函数中的重正子模糊性。我们探讨了SCET方法与QCD中以往方法之间的关系,并讨论了有效理论方法的优点。此外,我们从喷流和软函数的非线性光学计算中得出一个直观的教训,即当a->1时,有效理论中的因式分解是如何分解的。

英文摘要:

Using soft-collinear effective theory (SCET), which provides a unified framework for factorization, resummation of logarithms, and incorporation of universal nonperturbative functions in hard-scattering QCD cross-sections, we present a new prediction of angularity distributions in e+e- annihilation. Angularities tau_a are an infinite class of event shapes which vary in their sensitivity to the substructure of jets in the final state, controlled by a continuous parameter a<2. We calculate angularity distributions for all a<1 to first order in the strong coupling alpha_s and resum large logarithms in these distributions to next-to-leading logarithmic (NLL) accuracy. Our expressions for the next-to-leading order (NLO) O(alpha_s) partonic jet and soft functions in the factorization theorem for angularity distributions are given for the first time. We employ a model for the nonperturbative soft function with a gap parameter which cancels the renormalon ambiguity in the partonic soft function. We explore the relation between the SCET approach to resummation and past approaches in QCD, and discuss the advantages of the effective theory approach. In addition, we draw from the NLO calculations of the jet and soft functions an intuitive lesson about how factorization breaks down in the effective theory as a->1.

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