【作者】 王超；

【导师】 马连良； Cristinel DIACONU； Emmanuel MONNIER；

【作者基本信息】 山东大学 ， 粒子与原子核物理， 2017， 博士

【摘要】 希格斯玻色子和顶夸克对伴随产生机制是一种十分重要的希格斯玻色子产生机制,并且此产生机制迄今也没有被发现。因此寻找并发现此产生机制是一项非常吸引人的研究:不仅仅是第一次能够发现此产生机制,同时我们也可以测量希格斯粒子和顶夸克之间的Yukawa耦合作用。测量结果可以解答标准物理模型的一些基本问题,并且测量结果和标准模型预言结果的比较有可能揭示新物理的迹象。本论文主要探讨了利用三轻子末态寻找希格斯玻色子和顶夸克对伴随产生机制。在大型强子对撞机质心系能量为13 TeV的对撞能量下,本论文利用在大型强子对撞机上的ATLAS探测器所收集到的积分亮度为36.1 fb-1对撞数据进行物理分析。利用多变量分析(决策树)方法来对信号事例和本底事例进行有效的区分。对于主要的本底贡献-赝轻子背景事例,本论文采取了矩阵元方法进行评估。对于质量为125 GeV的标准物理模型的希格斯玻色子,超过背景事例假设2.2倍标准差的事例数被观测到,预测结果为1.5倍的标准差。经测量,希格斯玻色子和顶夸克对伴随产生机制的产生截面为标准物理模型所预计结果的1.5倍,符合标准物理模型中与顶夸克的Yukawa耦合预言结果。更多还原

【Abstract】 The production of the Higgs boson associated with a pair of top quarks is still not observed and is one of the most important Higgs boson production modes.Hence,the discovery of this production mode is a very attracting search:not only will it be the first time we can observe this Higgs production mode but also we will be able to measure its Yukawa coupling to the top quark.The measured results can answer the basic question of the Standard Model(SM)and can also search for any hints of new physics by comparing them to the SM prediction.An analysis of searching for the production of the Higgs boson associated with a pair of top quarks in three leptons final state is presented in this thesis.This analysis is performed with the collected data by the ATLAS detector in 2015 and 2016 during the so-called Run 2 campaign corresponding to an integrated luminosity of 36.1 fb-1 at a center of mass energy of(?)= 13 TeV.It uses a boosted decision tree algorithm to discriminate between signal and background.The dominant background of fake leptons is estimated with the data-driven method(Matrix Method).For a Standard Model Higgs boson of a 125 GeV mass,an excess of events over the expected background from other SM processes is found with an observed significance of 2.2 standard deviations,compared to an expectation of 1.5 standard deviations.The best fit for the t(?)H production cross section is 1.5-0.7+0.8 times the SM expectation,consistent with the value of the Yukawa coupling to top quarks in the Standard Model.更多还原