论文标题
在四个费米昂最终状态下的照片评估蒙特卡洛歧义
Evaluation of Photos Monte Carlo ambiguities in case of four fermion final states
论文作者
论文摘要
随着蒙特卡洛模拟应用的越来越多的精确要求和不断增长的应用程序，对此类模拟的不同组成部分的评估及其系统的歧义是最大的兴趣。在以下内容中，我们将解决蒙特卡洛（Monte Carlo）的系统错误问题，以模拟最终状态中的bremsstrahung校正，这些状态原则上不能将其确定为共振的衰减。这是可能的，因为该程序具有多体和多光子最终状态的相位空间的显式和精确参数化。对于某些过程的照片发射内核由完整的矩阵元素组成，在其余情况下，使用了适当的近似值。可以使用基于确切的相空间和精确固定顺序矩阵元素的生成器的模拟结果进行比较。出于此类验证的目的，照片提供了一种只能将排放限制为单个光子的选项。在目前的工作中，我们集中于$ q \ bar {q}（e^+e^ - ）\ to l^+l^ - l^+l^ - γ$和$γγ\ to l^+l^l^ - γ$过程的最终状态。用作交叉检查的参考分布是从固定阶Madgraph Monte Carlo模拟获得的。为了进行验证，我们专注于那些仅根据其设计来工作的相空间区域。这些硬性非校光光子的相位空间区域不会造成大的对数项。我们发现，在这些相空间区域中，照片和疯狂结果之间的差异并没有超过几％，而这些区域又对观察到的过程率贡献了约10％。鉴于可以精确计算现实的可观察到的可能的歧义，这令人鼓舞。
With the increasing precision requirements and growing spectrum of applications of Monte Carlo simulations the evaluation of different components of such simulations and their systematic ambiguities become of utmost interest. In the following, we will address the question of systematic errors for Photos Monte Carlo for simulation of bremsstrahlung corrections in final states, which can not, in principle, be identified as a decay of resonances. It is possible, because the program features explicit and exact parametrization of phase space for multi-body plus multi-photon final states. The Photos emission kernel for some processes consist of complete matrix element, in the remaining cases appropriate approximation is used. Comparisons with results of simulations, from generators based on exact phase space and exact fixed order matrix elements, can be used. For the purpose of such validations Photos provides an option to restrict emissions to single photon only. In the current work we concentrate on final state bremsstrahlung in $q \bar{q}(e^+e^-) \to l^+l^- l^+l^- γ$ and $γγ\to l^+l^- γ$ processes. The reference distributions used as a cross-check are obtained from the fixed-order MadGraph Monte Carlo simulations. For the purpose of validation we concentrate on those phase space regions where Photos is not expected to work on the basis of its design alone. These phase space regions of hard, non-collinear photons, do not contribute to large logarithmic terms. We find that in these phase space regions the differences between Photos and MadGraph results do not surpass a few percent and these regions, in turn, contribute about 10% to the observed process rates. This is encouraging in view of the possible ambiguities for precise calculation of realistic observables.
