"CR kinematics 8" of "Search for direct top squark pair production in final states with two leptons in $\sqrt{s} = 13$ TeV $pp$ collisions with the ATLAS detector"

The results of a search for direct pair production of top squarks in events with two leptons (electrons or muons) are reported, using 36.1 fb$^{-1}$ of integrated luminosity from proton--proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi}_{1}^{\pm}$ into a $b$-quark and the lightest chargino, the decay $\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi}_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi}_{1}^{0}$. No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the $\tilde{t}$ and $\tilde{\chi}_{1}^{0}$ masses. The results exclude at 95% confidence level $\tilde{\chi}_{1}^{0}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.

本文报道了利用大型强子对撞机（Large Hadron Collider, LHC）上ATLAS探测器采集的质心系能量sqrt{s}=13 TeV的质子-质子对撞数据（积分亮度为36.1 fb^{-1}），针对包含双轻子（电子或μ子）的事件开展顶超夸克（top squark， ilde{t}）直接成对产生的搜索结果。为覆盖顶超夸克与较轻超对称粒子间的多样质量差区间，本分析针对顶超夸克的四种典型衰变模式设置专属筛选方案：其一为 ilde{t}
ightarrow b ilde{chi}_{1}^{pm}衰变，即顶超夸克衰变为b夸克与最轻 chargino（ ilde{chi}_{1}^{pm}）；其二为 ilde{t}
ightarrow t ilde{chi}_{1}^{0}衰变，即顶超夸克衰变为在壳顶夸克与最轻中性伴子（neutralino， ilde{chi}_{1}^{0}）；此外还涵盖三体衰变 ilde{t}
ightarrow b W ilde{chi}_{1}^{0}与四体衰变 ilde{t}
ightarrow b ell
u ilde{chi}_{1}^{0}。所有筛选方案均未观测到显著超出标准模型本底的事件超额，据此以顶超夸克与 ilde{chi}_{1}^{0}的质量为变量设置了顶超夸克的实验限制。本结果在95%置信水平下，可排除最高约720 GeV的 ilde{chi}_{1}^{0}质量区间，拓展了此前同类搜索覆盖的超对称参数空间排除区域。