Measurement of the ttH production cross-section in the H to bb decay channel

这个博士项目是在ATLAS合作中定义的，致力于识别与顶夸克对相关的希格斯玻色子。这是ATLAS合作进行的最复杂的分析之一，因为低信号和高背景速率，加上将不确定性与实验和理论界仍然理解的背景过程相关联的困难，即与重味强子相关的顶夸克对。将有机会基于Run-3数据开发下一轮ttH分析。运行3将使当前数据集增加一倍以上。更大的数据集允许越来越多的差异测量，这对于通过希格斯有效场理论限制潜在的超越标准模型（BSM）效应是强有力的，同时也挑战了理论预测，需要改进建模以减少系统限制。将有开发新的机器学习方法的空间，以及将这些分析技术和算法所基于的正在进行的ATLAS开发纳入其中。这可以提高这些算法的性能，因为新的b标记算法和喷气对象正在开发中。希格斯粒子衰变为b-夸克的第t个过程为探测希格斯-顶耦合提供了最高的统计数据。分析将利用这些事件来探测高pT下的th过程，其中对BSM效应具有高灵敏度。重点将集中在两个方面：首先改进高pT事件的选择，导致所谓的增强事件，其次结合改进的主要顶夸克对背景模型。在分析团队中工作，博士生将改进用于选择增强希格斯玻色子的多元选择。该学生还将开发增强ttH（bb）信道的完全重建。这将允许对涉及顶夸克四向量的变量进行差分测量，这增加了对在增强状态下可能违反cp的希格斯-顶耦合的敏感性。这两个工作区域的结合将导致Run-2+3数据中ttH产量的差异测量，这将显著改善Run-2结果，并对BSM对希格斯-顶部耦合的贡献提供严格的约束。潜在的受益者包括：粒子物理学家和其他对标准模型内外的基本粒子有直接兴趣的人。在许多科学领域中大规模计算资源的使用者。物理系毕业生从研究生教学、项目和博士培训中获益。公司雇用我们的博士毕业生，他们将受益于他们的领先技能和能力，在充满挑战的国际环境中工作。

This PhD project is defined within the ATLAS collaboration, working on identifying Higgs bosons produced in association with a top-quark pair. This is one of the most complicated analyses performed by the ATLAS collaboration due the low signal and high background rates, coupled with the difficulties which come in associating uncertainties to a background process which is still being understood by the experimental and theoretical communities, namely top-quark pairs produced in association with heavy-flavour hadrons.There will be opportunities to develop the next round of the ttH analysis based on Run-3 data. Run 3 will more than double the current dataset. The larger dataset allows increasingly differential measurements that are powerful for constraining potential Beyond Standard Model (BSM) effects through Higgs Effective Field Theories, while also challenging the theory predictions and requiring improved modelling to reduce the systematic limitations. There will be scope to develop new machine learning methods as well as to incorporate ongoing ATLAS development that these analysis techniques and algorithms are based on. This could improve the performance of these algorithms as new b-tagging algorithms and jet objects are being developed.The ttH process where the Higgs decays into b-quarks offers the highest statistics to probe the Higgs-top coupling. The analysis will exploit these events to probe the ttH process at high pT, where there is high sensitivity to BSM effects. The focus will be on two areas: first improvements to the selection of high pT events, leading to so-called boosted events, and secondly by incorporating improved modelling for the dominant top-quark pair background. Working within the analysis team, the PhD student will improve the multivariate selection that is used to select boosted Higgs bosons. The student will also develop full reconstruction for the boosted ttH(bb) channel. This will allow differential measurements of variables involving the top-quark four-vectors that have increased sensitivity to a possible CP-violating Higgs-top coupling in the boosted regime. The combination of these two work areas will result in differential measurements of ttH production from Run-2+3 data that will significantly improve on the Run-2 results and provide tight constraints on BSM contributions to the Higgs-top coupling.Potential beneficiaries include:1. Particle physicists and others with a direct interest in fundamental particles, within and beyond the Standard Model.2. Users of large-scale computing resources in many fields of science.3. Physics graduates gaining from postgraduate teaching and projects as well as from PhD training within the group.4. Firms employing our PhD graduates who will benefit from their leading-edge skills and ability to work in challenging international environments.