Axion searches in rare Higgs decays at ATLAS

Axion 在 ATLAS 中搜索罕见的希格斯衰变

• 批准号: 2113367
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2113367
• 关键词: Axion; searches; rare; Higgs; decays

The discovery of a Standard Model like Higgs boson was a major milestone forthe LHC. Despite this, the Standard Model (SM) and the underlying theories sofar are plagued by problems that arise both theoretically and experimentally. Thisincludes the Strong CP-problem, which is the theoretical argument that the SMcould break CP symmetry in strong interactions. However, no evidence of suchhas been experimentally observed. The Higgs boson observation with a mass ofapproximately 125 GeV does leave open the possibility for new particles which willnot violate the elementary gauge symmetries of the Standard Model and as suchcreates the potential to search for these particles at low mass .With this motivation my project will contribute to the searches of such particles.The aim is to initiate the analysis for searching for a pseudo-scalar low mass particlewhich we will call a, from the rare Higgs decay to Za. Particle a could identifyas a possible Axion-like particle (ALP) or Next-to-Minimal Supersymmetry Model(NMSSM) candidate.Axions and ALP's are theoretical particles resulting from the Peccei-Quinnmechanism that describes a possible solution to the CP problem by introducinga dynamic field to explain the CP-violating term, ALP's can couple to all SMparticles, however depending on their coupling and possible mass ranges searchesfor ALP's differ significantly. Theoretical studies by Bauer (2017) show that thereare possible parameter regions present were LHC data could well be utilized tosearch for ALPs in the decay channel H Za for masses in the range 0.1-10 GeVand could be long lived In Higgs physics, ALP's could decay into a pair ofjets or photons alongside a Z-boson decaying into two leptons with a clean signal.Previous searches for ALPs have been conducted at the LHC but have so far notbeen successful.A challenge with this study is the fact that R, the distance the ALP's photonsare from each other, is so small that during photon identification (ID) photons areactually being misidentified. A major task of this project will focus on the analysisof these photons by evaluating the substructure of the photon shower in the 1stlayer of the electromagnetic calorimeter (ECAL) to better distinguish those thatare misidentified and as such improve the overall analysis of this decay channel.Machine learning approaches such as deep neural networks and other multivariateanalysis techniques, complemented by skills gained through working as part of theLiverpool data intensive center for doctoral training (LIV.DAT), will be exhaustivelyattempted for better photon reconstruction. By incrementally improvingissues related to the underlying analysis of this decay channel can pseudo-scalarlow mass particles and such be thoroughly investigated

像希格斯玻色子这样的标准模型的发现是大型强子对撞机的一个重要里程碑。尽管如此，标准模型（SM）和基础理论仍然受到理论和实验上出现的问题的困扰。这包括强CP-问题，这是SM在强相互作用中可以打破CP对称性的理论论证。然而，没有证据表明这样的实验观察。质量约为125 GeV的希格斯玻色子的观测确实为不违反标准模型基本规范对称性的新粒子的存在提供了可能性，因此创造了在低质量下寻找这些粒子的可能性。基于这一动机，我的项目将致力于这类粒子的寻找。目的是开始分析寻找一种赝-标量低质量粒子，我们称之为a，从希格斯衰变到Za。粒子a可能是类轴子粒子（Axion-like particle，ALP）或次最小超对称模型（Next-to-Minimal Supersymmetry Model，NMSSM）的候选粒子。轴子和类轴子粒子是由Peccei-Quinn机制产生的理论粒子，该机制通过引入动态场来解释CP破坏项，描述CP问题的可能解决方案，ALP粒子可以耦合到所有SM粒子，然而，根据它们的耦合和可能的质量范围，对ALP的搜索显着不同。Bauer（2017）的理论研究表明，存在可能的参数区域，LHC数据可以很好地用于在0.1-10 GeV的质量范围内搜索衰变通道H Za中的ALP，并且可以长时间存在。ALP可以衰变成一对射流或光子，玻色子衰变成两个带有清晰信号的轻子。以前在大型强子对撞机上进行过ALP的搜索，但迄今为止还没有成功。这项研究的一个挑战是，ALP的光子彼此之间的距离是如此之小，以至于在光子识别（ID）过程中，光子实际上被错误识别。该项目的一项主要任务将侧重于通过评估电磁量热计（ECAL）第一层中光子簇射的子结构来分析这些光子，以更好地区分那些被错误识别的光子，从而改善对这些光子的整体分析。衰变通道。机器学习方法，例如深度神经网络和其他多变量分析技术，作为利物浦数据密集型博士培训中心（LIV.DAT）的一部分，我们将尽全力尝试更好的光子重建。通过逐步改进与这种衰变通道的基本分析有关的问题，可以彻底研究伪标量低质量粒子等