ATLAS实验上利用喷注子结构技术研究希格斯子伴随顶夸克对产生过程

After the discovery of the Higgs particle, it is natural to measure as precise as possible its couplings. They are fundamental to confirm whether the found particle is the Higgs boson predicted by the Standard Model or by any other models that might connect to new physics. Determination of the top-Higgs Yukawa coupling is certainly one of the most important tasks. While it is possible to derive this coupling via the loop corrections to the gluon/photon-Higgs couplings with the strong assumption of no contributions from new physics, Higgs production associated with top quark pair provides the unique opportunity to measure the top-Higgs coupling directly. We propose to investigate the boosted ttH,H->bb process with novel jet substructures, which will allow clear separation of the signal process from the enormous QCD multi-jet and top quark pair background processes. The separation will be further strengthened with dedicated bottom quark tagging techniques and the modern deep learning method. With around 100 fb^-1 pp collision data collected by the ATLAS detector over the next three years, it is expected to discover this ttH,H->bb process and measure roughly the top-Higgs Yukawa coupling.

在希格斯粒子发现之后，实验上迫切要求尽量准确测量与之相关的耦合常数。这对于确认所发现的粒子是否为标准模型所预测的希格斯波色子或是其它超出标准模型所预言的粒子，而后者往往与新物理存在联系。测量顶夸克-希格斯子的汤川耦合常数便是其中重要的任务之一。该常数可以通过测量胶子/光子与希格斯子的耦合常数，考虑圈图贡献间接得出，但是通常需要假设没有来自新物理的额外贡献。而希格斯子伴随顶夸克对产生过程可以提供唯一直接测量的机会。本项目拟使用新颖的喷注子结构技术，标记洛伦茨加速的ttH,H->bb过程，与其它本底过程分离。通过引入高效的底夸克标记方法，结合最新的深度学习方法，可以增强信号与本底的分离效果。预计利用未来三年ATLAS探测器采集的约100 fb^-1质子-质子对撞事例，可以发现该ttH,H->bb过程，并初步测量顶夸克-希格斯子的汤川耦合常数。

准确测量希格斯粒子性质是大型强子对撞机实验最重要的研究课题之一。其中，ttH,H->bb物理过程可以直接测量顶夸克-希格斯子的汤川耦合常数，对确定希格斯粒子性质十分关键。本研究利用超面环仪探测器（ATLAS）收集的13TeV实验数据，过提高复杂末态带电粒子径迹重建效率和精度，从根本上提高底夸克标记性能。分析过程中采用喷注子结构技术提高H->bb标记效率，并结合多变量分析方法提高信号事例显著性。分析方法与所用技术得到验证，测量所得信号强度与标准模型预测相符。但受限于有限的实验数据，尚未直接发现该物理过程。