"Figure 10b" of "Constraints on spin-0 dark matter mediators and invisible Higgs decays using ATLAS 13 TeV $pp$ collision data with two top quarks and missing transverse momentum in the final state"

This paper presents a statistical combination of searches targeting final states with two top quarks and invisible particles, characterised by the presenceof zero, one or two leptons, at least one jet originating from a $b$-quark and missing transverse momentum.The analyses are searches for phenomena beyond the Standard Model consistent with the direct production of dark matter in $pp$ collisions at the LHC, using 139 fb$^{-\text{1}}$ of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV.The results are interpreted in terms of simplified dark matter models with a spin-0 scalar or pseudoscalar mediator particle. In addition,the results are interpreted in terms of upper limits on the Higgs boson invisible branching ratio, where the Higgs boson is producedaccording to the Standard Model in association with a pair of top quarks.For scalar (pseudoscalar) dark matter models, with all couplings set to unity, the statistical combination extends the mass range excluded by the best of the individual channels by 100 (30) GeV, excluding mediator masses up to 370 GeV.In addition, the statistical combination improves the expected coupling exclusion reach by 14\% (24\%), assuming a scalar (pseudoscalar) mediator mass of 10 GeV.An upper limit on the Higgs boson invisible branching ratio of 0.38 ($\text{0.30}^{+\text{0.13}}_{-\text{0.09}}$) is observed (expected) at 95\% confidence level.

本论文针对末态包含两个顶夸克（top quark）与不可见粒子的搜寻分析开展统计组合研究，该类信号的特征为存在0、1或2个轻子（lepton）、至少一个源自b夸克（b-quark）的喷注（jet）以及缺失横向动量（missing transverse momentum）。本分析利用大型强子对撞机（Large Hadron Collider, LHC）上ATLAS探测器（ATLAS）在13 TeV质心系能量下采集的139 fb⁻¹数据，搜寻与pp碰撞中暗物质直接产生相符的超出标准模型（Standard Model）的新物理现象。研究结果基于带有自旋0标量（spin-0 scalar）或赝标量（pseudoscalar）媒介粒子的简化暗物质模型进行诠释。此外，研究结果还针对希格斯玻色子（Higgs boson）的不可见分支比（branching ratio）给出上限：其中希格斯玻色子按标准模型伴随一对顶夸克产生。对于所有耦合强度设为1的标量（赝标量）暗物质模型，本次统计组合分析将单个最优分析通道的排除质量范围拓展了100（30）GeV，可排除最高达370 GeV的媒介粒子质量。此外，假设标量（赝标量）媒介粒子质量为10 GeV时，本次统计组合分析将预期的耦合强度排除灵敏度提升了14%（24%）。在95%置信水平（confidence level）下，观测到的希格斯玻色子不可见分支比上限为0.38，预期上限为$ ext{0.30}^{+ ext{0.13}}_{- ext{0.09}}$。