The search for pair production of Higgs Bosons at the ATLAS experiment

Iza博士项目的目标是完成世界领先的分析，寻找新的现象，并使用di-Higgs产生，特别是四个b夸克的最终状态来限制Higgs自耦合的价值。Higgs玻色子对产生是一个关键的通道，对许多新的物理现象和Higgs部门的修改敏感，也是Higgs自耦合和扩展Higgs势的重要测量。虽然一个完整的测量可能需要高亮度LHC的全部亮度，但大型Run-2数据集是敏感的探针，已经能够限制这种重要的耦合。Iza将在牛津大学ATLAS Exotics小组工作，也将在ATLAS合作的各个分析小组中合作和工作。她将专注于分析来自LHC Run-2（2015-2018）的ATLAS数据，以寻找di-Higgs产生的证据。她将研究二希格斯衰变为四个b夸克的过程，寻找新的共振和非共振现象的证据。后者的一个重要方面将是理解和改进如何使用现有的大型数据集来约束希格斯自耦合的不同值。她还将研究Run-2搜索通道的组合，其中最敏感的是4 b，bbtautau，bbyy和bblnulnu。这些通道的组合，每个都使用完整的140 fb-1的运行2数据（几乎是以前最好结果的四倍），将允许对SM耦合进行更强大的约束，或提供非SM耦合值的证据。这是一项艰巨的任务，需要每个分析渠道的贡献者付出大量努力，以了解其相对敏感性和贡献。她将需要了解不同渠道之间的系统和统计相关性，并开发在此特定分析中适当考虑这些相关性的工具。特别是，已经有了很多理论上的进展，导致更精确的预测和在有效场论方法中模拟BSM物理的能力，这将需要相当多的工作来充分理解，并优化结果的灵敏度和可视化。为了提高对包含希格斯衰变到b夸克对的最终状态的灵敏度，她将需要校准和开发新的，先进的b夸克识别算法。她将致力于原位校准b标记算法的方法，使用高pT胶子分裂到bb的样本直接提供这种拓扑结构中的校正因子。正在开发使用机器学习技术的专用高级b-强子标记器，其性能显著。通常这些都不能用传统方法校准，但这些技术可能提供一种替代途径，改善整个ATLAS物理计划的希格斯喷流标记。这项工作将使她处于理想的位置，以分析2021年和2022年的第一批Run-3数据，新的碰撞能量为14 TeV。她将能够确保b标记尽可能高的性能，这对于在该签名中使用Run-3数据的大亮度进行世界领先的分析至关重要。她将在CERN度过她的第二年，尽可能接近实验室和数据采集，并在ATLAS合作中获得知名度。

The aim of Iza's PhD project is to accomplish world-leading analyses looking for new phenomena and constraining the value of the Higgs self-coupling using di-Higgs production, specifically the four b-quark final state.Higgs boson pair production is a critical channel, sensitive to many new physics phenomena and modifications to the Higgs sector, and also an important measurement of the Higgs self-coupling and the extended Higgs potential. Though a full measurement may need the full luminosity of the High Luminosity LHC, the large Run-2 datasets are sensitive probes, already able to constrain this vital coupling.Iza will work within the Oxford ATLAS Exotics group in the department and also will collaborate and work in the respective analysis groups within the ATLAS collaboration. She will focus on analysing ATLAS data from LHC Run-2 (2015-2018) for evidence of di-Higgs production. Working on the di-Higgs decay to four b-quarks, she will search for evidence of new resonant and non-resonant phenomena. An important aspect of the latter will be to understand and improve how different values of the Higgs self-coupling can be constrained using the large datasets now available. She will also work on the combination of the Run-2 search channels, the most sensitive of which are 4b, bbtautau, bbyy and bblnulnu. The combination of these channels, each using the full 140 fb-1 of Run-2 data (nearly four times that of the best previous result) will allow for much more powerful constraints on the SM coupling, or provide evidence of a non-SM coupling value. This is a major undertaking, requiring a great deal of effort from contributors working on each of the analysis channels to understand their relative sensitivities and contributions. She will need to understand the systematic and statistical correlations within the different channels and develop tools that properly account for them in this particular analysis. In particular, there has been a lot of theoretical progress, resulting in more precise predictions and ability to model BSM physics in an effective field theory approach, which will require considerably more work to understand fully, and optimise both the sensitivity and visualisation of the results.To improve the sensitivity to final states containing Higgs decays to b-quark pairs, she will need to calibrate and develop new, advanced b-quark identification algorithms. She will work on means of calibrating b-tagging algorithms in-situ, using samples of high-pT gluon splitting to bb to provide correction factors in this topology directly. Dedicated advanced b-hadron taggers using machine learning techniques are being developed which gain significant performance. Often these cannot be calibrated by conventional means, but these techniques may provide an alternative route, improving Higgs jet tagging across the ATLAS physics programme.This work will leave her ideally placed to analyse the first Run-3 data due in 2021 and 2022, at a new record collision energy of 14 TeV. She will be able to ensure that b-tagging is as performant as possible, which will be vital for world-leading analyses using large luminosities of Run-3 data in this signature. She will spend her second year at CERN to be as close as possible to the laboratory and data-taking, and to gain visibility within the ATLAS Collaboration.