Top-Quarks under the LHC's Magnifying Glass: From Process Modelling to Parameter Extraction

随着2010年碰撞的成功开始，LHC为彻底探索Terascale物理学奠定了又一个里程碑。它的第一次研究运行于2010-2013年，初始能量为7 TeV，从2012年上升到8 TeV。经过近两年的关闭，LHC于2015年开始提供物理数据。这标志着LHC Run 2时代的开始，并为更深入地理解标准模型（SM）物理学开辟了道路，并有望获得新的发现。在LHC观测到的多粒子事件隐藏或强烈修改了SM之外的所有可能的物理信号。因此，鉴于新物理信号的正确解释，这可能是从数据中提取的，它是非常感兴趣的，以减少SM过程的理论不确定性。即尽可能准确地理解它们。当涉及到QCD（背景）过程时，这一点尤其重要。在这方面，需要精确的次领先阶（NLO）QCD计算的物理观测值是无可争议的。ATLAS和CMS在大型强子对撞机上进行的关键测量与顶夸克有关，顶夸克是已知最重的基本粒子。除了确定顶夸克质量外，关键的测量还包括总截面、微分分布以及自旋相关和顶夸克与规范玻色子和SM希格斯玻色子的耦合。然而，顶夸克是一种寿命极短的共振，只有它的衰变产物才能被实验检测到。因此，为了与数据进行比较，理论预测必须包括顶夸克衰变。此外，由于大型强子对撞机的大碰撞能量，大量产生具有大能量和高pT的顶对。因此，初态胶子辐射的概率增加，使得ttj末态具有高统计可测性。除了完全包含的QCD tt产生和ttj产生过程之外，在LHC上可以访问更多的排他性最终状态。尽管它们的横截面通常要小得多，但它们可以提供关于顶夸克性质的关键信息，例如顶夸克与规范玻色子的耦合。本计画的目的是提供精确且符合实际的理论预测，以预测与其他终态相关的tt产生。在实践中，这需要包括对顶夸克产生和衰变的QCD修正，包括顶夸克自旋相关。更精确地说，我们将集中计算非线性光学量子色动力学修正完全现实的最终状态与完整的顶夸克离壳效应。我们计划使用我们的现实的理论结果，研究在大型强子对撞机顶夸克物理学的广泛的唯象方面。

With the successful start of collisions in 2010, the LHC has put another milestone towards a thorough exploration of physics at the Terascale. Its first research run took place from 2010-2013 at an initial energy of 7 TeV, rising to 8 TeV from 2012. After an almost two year shutdown, the LHC started delivering physics data in 2015. This marked the beginning of the LHC Run 2 era and opened the path to an even deeper understanding of the Standard Model (SM) physics and hopefully to new discoveries. The multi-particle events that are observed at the LHC hide or strongly modify all possible signals of physics beyond the SM. Thus, in view of a correct interpretation of the signals of new physics which might be extracted from data, it is of great interest to reduce theoretical uncertainties for the SM processes. i.e. to understand them as precisely as possible. This is especially important when QCD (background) processes are involved. In this respect, the need of precision next-to-leading order (NLO) QCD calculations for physical observables is indisputable. Key measurements that are curried out at the LHC by ATLAS and CMS are connected to the top-quark, the heaviest known fundamental particle. Besides the determination of the top-quark mass, key measurements include the total cross section, differential distributions as well as spin correlations and top-quark couplings to gauge bosons and the SM Higgs boson. The top-quark, however, is an extremely short-lived resonance and only its decay products can be detected experimentally. Thus, for comparison with data, theoretical predictions must include top-quark decays. Moreover, due to the large collision energy at the LHC, top anti-top pairs are abundantly produced with large energy and high pT . Therefore, the probability for the initial state gluon radiation increases making the ttj final state measurable with high statistics. Besides fully inclusive QCD tt production and the ttj production process, more exclusive final states can be accessed at the LHC. Even though their cross sections are typically much smaller, they can provide key information on the properties of the top-quark like for example top-quark couplings to gauge bosons. The purpose of this project is to provide precise and realistic theoretical predictions for tt production in association with additional final states. In practice this requires to include QCD corrections to top-quark production and decays including top-quark spin correlations. To be more precise, we shall focus on calculating NLO QCD corrections to fully realistic final states with complete top-quark off-shell effects included. We plan to use our realistic theoretical results to study broad phenomenological aspects of top-quark physics at the LHC.