"Figure 9b" 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）：本研究针对质心系能量√s=13 TeV下的异号双轻子末态，开展顶超对称夸克（top squark）与暗物质粒子（dark matter particle）的搜寻工作。本次分析使用2016年由CMS探测器（CMS）采集的、积分亮度达35.9 fb⁻¹的13 TeV质子-质子碰撞数据，探索包含两个异号轻子（电子或μ子）、b标记喷注以及横向缺失动量（pTmiss）的末态新物理信号。通过对横向缺失动量与横向质量变量施加筛选条件，可有效将假设的信号事件与占主导的顶夸克对（ttbar）背景区分开来。本次搜寻未观测到与预期背景存在显著偏离的信号。本分析在成对产生顶超对称夸克的简化超对称模型（simplified supersymmetric models）框架下设置了排除极限：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质量排除上限可达800 GeV，最轻中性微子的质量排除上限可达360 GeV；结合单轻子与全喷注末态的搜寻结果，上述排除上限可进一步提升至最轻顶超对称夸克1050 GeV、最轻中性微子500 GeV。对于通过荷微子（chargino）与标量轻子（slepton）发生级联衰变的顶超对称夸克，其质量限制可达顶超对称夸克1300 GeV、最轻中性微子800 GeV。本结果还在通过标量传递子（scalar mediator）或赝标量传递子（pseudoscalar mediator）与顶夸克耦合的暗物质（dark matter, DM）简化模型中得到阐释：针对轻暗物质粒子，标量传递子的质量排除上限可达100 GeV，赝标量传递子则为50 GeV，其中标量传递子相关结果是该模型迄今最为严苛的限制之一。