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

这个博士项目是在ATLAS合作项目中定义的，致力于识别与顶夸克对相关产生的希格斯玻色子。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率，再加上将不确定性与实验和理论界仍在理解的背景过程联系起来的困难，即与重味道强子有关的顶夸克对。将有机会开发基于RUN-3数据的下一轮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不同的测量，这些测量通过希格斯有效场论约束超越标准模型(BSM)效应的潜力，同时也挑战理论预测，并要求改进建模以减少系统限制。将有机会开发新的机器学习方法，以及纳入这些分析技术和算法所基于的正在进行的ATLAS开发。随着新的b标记算法和喷注物体的开发，这可能会提高这些算法的性能。在TTH过程中，希格斯衰变成b夸克，为探测Higgs-Top耦合提供了最高的统计信息。分析将利用这些事件来探测对BSM效应高度敏感的高PT下的TTH过程。重点将集中在两个领域：第一，改进高PT事件的选择，导致所谓的增强事件，第二，通过纳入主要的顶夸克对背景的改进的模型。在分析团队中工作，这位博士生将改进用于选择增强希格斯玻色子的多变量选择。学生还将对增强的TTH(BB)通道进行完全重建。这将允许对涉及顶夸克四个矢量的变量进行差异测量，这些变量增加了对增强区域中可能违反CP的希格斯-TOP耦合的敏感性。这两个工作领域的结合将导致从RUN-2+3数据对TTH产生的不同测量，这将显著改善RUN-2结果，并对BSM对希格斯-TOP耦合的贡献提供严格的限制。潜在的受益者包括：1.粒子物理学家和其他对基本粒子直接感兴趣的人，在标准模型之内和之外。用户拥有多个科学领域的大规模计算资源。物理毕业生从研究生教学和项目以及集团内的博士生培训中获益。聘用我们博士毕业生的公司将受益于他们的前沿技能和在充满挑战的国际环境中工作的能力。

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.