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

在 ATLAS 实验中寻找希格斯玻色子的配对产生

• 批准号: 2275245
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2275245
• 关键词: search; pair; production; Higgs; Bosons

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.

Iza博士项目的目标是完成世界领先的分析，寻找新的现象，并利用双Higgs产生，特别是四个b夸克末态来约束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对Higgs部门的修改很敏感，也是测量Higgs自耦合和扩展Higgs势的重要手段。尽管完整的测量可能需要高亮度大型强子对撞机的全部光度，但大型RUN-2数据集是敏感的探测器，已经能够限制这种重要的耦合。Iza将在该部门的牛津ATLAS Exotics小组内工作，也将在ATLAS协作内的各个分析小组中进行协作和工作。她将专注于分析大型强子对撞机RUN-2(2015-2018)的ATLAS数据，以寻找双希格斯粒子产生的证据。通过研究双希格斯衰变到四个b夸克，她将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限制不同的希格斯自耦合数值。她还将研究Run-2搜索频道的组合，其中最敏感的是4b、bbtautau、bbyy和bblnulnu。这些通道的组合(每个通道使用完整的140 FB-1运行数据(几乎是之前最佳结果的四倍)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。这是一项重大任务，需要每个分析渠道的贡献者付出大量努力，以了解它们的相对敏感性和贡献。她将需要了解不同渠道内的系统和统计相关性，并开发工具，在这一具体分析中适当地解释这些相关性。特别是，已经有了大量的理论进展，导致了更精确的预测和用有效的场论方法模拟BSM物理的能力，这将需要相当多的工作来完全理解，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夸克对的终态的灵敏度，她将需要校准和开发新的、先进的b夸克识别算法。她将致力于现场校准b标记算法的方法，使用高PT胶子分裂到bb的样本来直接在这种拓扑中提供修正因子。使用机器学习技术的专用高级b-强子标记器正在开发中，获得了显著的性能。通常情况下，这些数据不能通过传统方法进行校准，但这些技术可能会提供另一种途径，改进整个ATLAS物理计划中的希格斯喷注标记。这项工作将使她处于分析定于2021年和2022年首次运行-3数据的理想位置，碰撞能量达到14TeV的新纪录。她将能够确保b标记的性能尽可能好，这对于在此签名中使用大亮度RUN-3数据进行世界领先的分析至关重要。她将在欧洲核子研究中心度过她的第二年，以便尽可能接近实验室和数据采集，并在ATLAS合作中获得知名度。