"Figure 8b" of "Search for top squarks and dark matter particles in opposite-charge dilepton final states at $\sqrt{s}=$ 13 TeV"

CERN-LHC. Search for top squarks and dark matter particles in opposite-charge dilepton final states at sqrt(s) = 13 TeV A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b quarks, and missing transverse momentum (pTmiss). The search uses proton-proton collision data at 13 TeV amounting to 35.9 $fb^{−1}$ of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant ttbar background with requirements on pTmiss and transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.

欧洲核子研究中心大型强子对撞机（CERN-LHC）：√s=13 TeV下异号双轻子末态的顶超对称夸克与暗物质粒子搜索

本研究针对包含两个异号轻子（电子或μ子）、被标记为起源于b夸克的喷注，以及横向缺失动量（missing transverse momentum, $p_ ext{T}^ ext{miss}$）的末态，开展新物理搜索。本次分析使用2016年CMS探测器采集的13 TeV质子-质子对撞数据，积分亮度达35.9 fb⁻¹。

通过对横向缺失动量与横向质量变量施加筛选条件，可将假设的信号事件与占主导的顶夸克对（$tar{t}$）背景有效区分开。经分析，未观测到与预期背景存在显著偏差。

在成对产生顶超对称夸克（top squark）的简化超对称模型框架内，我们设置了95%置信度的排除极限。针对仅衰变至顶夸克与中性微子（neutralino）的顶超对称夸克，在95%置信度下，最轻顶超对称夸克的排除质量上限可达800 GeV，最轻中性微子的排除质量上限可达360 GeV。结合单轻子与全喷注末态的搜索结果，顶超对称夸克的排除质量上限可提升至1050 GeV，最轻中性微子的排除质量上限可提升至500 GeV。

对于通过荷电微子（chargino）与轻子伴子（slepton）进行级联衰变的顶超对称夸克，其排除质量上限可达1300 GeV，最轻中性微子的排除质量上限可达800 GeV。

本结果还在通过标量或赝标量媒介子与顶夸克耦合的暗物质（dark matter, DM）简化模型中得到诠释。针对轻暗物质，标量媒介子的排除质量上限可达100 GeV，赝标量媒介子的排除质量上限可达50 GeV。该标量媒介子相关结果，是该模型迄今最为严苛的限制之一。