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arXiv 1709.04656hep-phhep-ex
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次领先阶精度下的单顶夸克产生的矩阵元方法

Single top-quark production with the Matrix Element Method in next-to-leading order accuracy

Till Martini, Peter Uwer

摘要:

单顶夸克的产生为标准模型的精确测试和可能扩展的搜索提供了一个独特的实验室。此外,在标准模型的假设下,单顶夸克产生可以用来确定顶夸克相关耦合。为了精确地确定电弱规范耦合或顶夸克质量等参数,需要有效的、无偏的和理论上明确的分析方法。在这种情况下,矩阵元法(MEM)已经建立在强子对撞机分析,由于其可能性,以利用实验数据中的信息。然而,到目前为止,它主要是应用在玻恩近似。我们讨论的扩展到下一个到领先的顺序(NLO)的准确性。作为必要的前提,我们介绍了一种有效的方法来计算喷注事件的非线性光学QCD重量。作为概念的证明和代表性的例子,我们使用MEM在NLO再现顶夸克质量在一个玩具实验中,我们把单顶夸克事件产生的NLO精度作为伪数据。这是第一次应用的MEM在NLO精度强子生产的喷气机起源于有色末态部分子。我们观察到,分析非线性光学事件与玻恩似然可以引入一个明显的偏差,在提取的质量,这将需要显着的校准与相关的不确定性。虽然我们专注于参数的确定,这里提出的方法也可以用来搜索新的物理使用似然比。

英文摘要:

Single top-quark production offers a unique laboratory for precision tests of the Standard Model and searches of possible extensions. Furthermore, assuming the Standard Model, single top-quark production can be used to determine top-quark related couplings. For precise determinations of parameters like the electroweak gauge couplings or the mass of the top quark, efficient, unbiased, and theoretically unambiguous analysis methods are needed. Within this context, the Matrix Element Method (MEM) has been established in hadron collider analyses due to its possibility to top out at utilising the information available in experimental data. However, so far it has mostly been applied in Born approximation only. We discuss the extension to next-to-leading order (NLO) accuracy. As a necessary prerequisite we introduce an efficient method to calculate NLO QCD weights for jet events. As proof of concept and representative example we use the MEM at NLO to reproduce the top-quark mass in a toy experiment where we treat single top-quark events generated at NLO accuracy as pseudo-data. This is the first application of the MEM at NLO accuracy to the hadronic production of jets originating from coloured final state partons. We observe that analysing NLO events with Born likelihoods can introduce a pronounced bias in the extracted mass which would require significant calibration with associated uncertainties. Although we focus on parameter determinations, the methods presented here can also be used to search for new physics using likelihood ratios.

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