arXiv 0906.40522009-06hep-ph

NLO部分子簇射矩阵元与精确相空间的匹配：W -> 1 nu（gamma）和gamma^* -> pi^+pi^-（gamma）情形

Matching NLO parton shower matrix element with exact phase space: case of W -> l nu (gamma) and gamma^* -> pi^+pi^-(gamma)

G. Nanava, Qingjun Xu, Z. Was

备注：: 24 pages
发表信息：: Eur.Phys.J.C70:673-688,2010
DOI：: 10.1140/epjc/s10052-010-1454-8

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摘要：

PHOTOS Monte Carlo常用于模拟中间粒子和共振衰变中的QED效应。动量是以这样一种方式产生的，即事件的样本覆盖整个韧致辐射相空间。在选择切割的帮助下，可以考虑实验验收。该程序是基于一个精确的多光子相空间。粗矩阵元素是通过一个通用的多维核的迭代。它确保了软光子区域的精确分布。算法兼容互斥取幂。为了评估程序的精度，有必要借助微扰结果来控制内核。如果可用，则从精确的一阶矩阵元素构造核。这确保了非前导序列所需的所有项都被考虑在内。在本文中，我们将集中讨论W -> l nu和γ ^* -> pi^+ pi^-衰变。两个过程的玻恩能级截面在相空间的某些点接近于零。一个过程相关的补偿权重被构造成包含精确的矩阵元素，但建议仅在测试中使用。在硬光子区域，标量QED不被认为是可靠的，γ ^* 衰变的补偿权重可能很大。就总比率而言，影响保持在千分之一水平。尽管如此，它仍然是有趣的。导致这种效应的项类似于QCD中出现的某些项。本文既可理解为讨论如何在与精确完备的相空间、互斥指数和标量QED（标量QED）一阶矩阵元相容的条件下匹配带电源的两条共线发射链，也可理解为加速器实验预言的实用研究。

英文摘要：

The PHOTOS Monte Carlo is often used for simulation of QED effects in decay of intermediate particles and resonances. Momenta are generated in such a way that samples of events cover the whole bremsstrahlung phase space. With the help of selection cuts, experimental acceptance can be then taken into account. The program is based on an exact multiphoton phase space. Crude matrix element is obtained by iteration of a universal multidimensional kernel. It ensures exact distribution in the soft photon region. Algorithm is compatible with exclusive exponentiation. To evaluate the program's precision, it is necessary to control the kernel with the help of perturbative results. If available, kernel is constructed from the exact first order matrix element. This ensures that all terms necessary for non-leading logarithms are taken into account. In the present paper we will focus on the W -> l nu and gamma^* -> pi^+ pi^- decays. The Born level cross sections for both processes approach zero in some points of the phase space. A process dependent compensating weight is constructed to incorporate the exact matrix element, but is recommended for use in tests only. In the hard photon region, where scalar QED is not expected to be reliable, the compensating weight for gamma^* decay can be large. With respect to the total rate, the effect remains at the permille level. It is nonetheless of interest. The terms leading to the effect are analogous to some terms appearing in QCD. The present paper can be understood either as a contribution to discussion on how to match two collinear emission chains resulting from charged sources in a way compatible with the exact and complete phase space, exclusive exponentiation and the first order matrix element of QED (scalar QED), or as the practical study of predictions for accelerator experiments.

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。

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