Measurement of Higgs plus Associated Top Production in the Boosted Regime

2012年在大型强子对撞机上发现希格斯玻色子后，仍有许多测量需要进行，以验证它是标准模型希格斯玻色子，还是更奇怪的东西。在ATLAS的合作中，这个项目关注的是希格斯玻色子与一对顶夸克联合产生，然后衰变为b夸克的通道。在SM中，费米子与希格斯粒子的耦合与费米子质量成正比，因此精确测量这些耦合是至关重要的，这种耦合被称为汤川耦合。对预测耦合强度的任何偏离都将是SM以外的新物理学的有力指示，对我们对大尺度物理学的理解将产生深远的影响。该项目将利用相空间的特定区域，在那里顶夸克和/或希格斯玻色子被提升到比它们的静止质量大得多的高横向动量。在这种运动学状态下，顶部或希格斯粒子的衰变产物被准直成一股“胖”喷流。可以识别这些事件，以选择高信号纯度的样本进行分析。还可以使用专门设计的技术来观察这些肥大喷气机的子结构，以确定它们来自特定的重物。该项目将建立在半轻子模式(其中一个顶部强子衰变，一个轻子衰变)的第一次测量的基础上，最初的目标是使用完整的RUN-2数据集将其扩展到全强子模式(其中两个顶夸克都强子衰变)。在这两种模式中，都有大量的组合问题，必须使用精细化的变量集来克服。这些变量将被用作深度神经网络的输入，这将提高结果的统计意义。该项目将使用稳健的统计技术来结合来自不同模式和渠道的结果。

Following the discovery of the Higgs Boson at the LHC in 2012, there remain many measurements to be made to verify whether it is a Standard-Model Higgs boson, or something more exotic. Within the ATLAS collaboration, this project focuses on the channel where a Higgs boson is produced in association with a pair of top quarks, and then decays to b-quarks. In the SM, the coupling of fermions to the Higgs is proportional to the fermion mass and so accurate measurements of these couplings, called Yukawa couplings, is crucial. Any deviation from the predicted coupling strengths would be a powerful indication of new physics beyond the SM, with far-reaching consequences for our understanding of physics at large scales. The project will exploit the specific region of phase space where the top quarks and/or the Higgs boson are boosted to high transverse momenta, considerably larger than their rest mass. In this kinematic regime, the decay products of the top or Higgs are collimated into one "fat" jet. These events can be identified to select a high signal-purity sample to analyse. Specifically designed techniques looking at the substructure of these fat jets can also be used to identify them as originating from a specific heavy object. The project will build upon first measurements made in the semi-leptonic mode (where one top decay hadronically and one leptonically) with an initial aim to extend this to the all-hadronic mode (where both top quarks decay hadronically) using the full Run-2 dataset. In both modes there are large combinatorial problems which must be overcome using a refined set of variables. These variables will be used as inputs to a deep neural network which should improve the statistical significance of the results. The project will use robust statistical techniques to combine the results from different modes and channels.