Search for Supersymmetry in events with $b$-tagged jets and missing transverse energy in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for the supersymmetric partner of the Standard Model bottom and top quarks is presented. The search uses 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. Direct production of pairs of bottom and top squarks ($\tilde{b}_1$ and $\tilde{t}_1$) is searched for in final states with $b$-tagged jets and missing transverse momentum. Distinctive selections are defined with either no charged leptons (electrons and muons) in the final state, or one charged lepton. The zero-lepton selection targets models in which the $\tilde{b}_1$ is the lightest squark and is assumed to decay via $\tilde{b}_1 \rightarrow b \tilde{\chi}_1^0$, where $\tilde{\chi}_1^0$ is the lightest neutralino. The one-lepton final state targets models where bottom or top squarks are produced and can decay into multiple channels, $\tilde{b}_1 \rightarrow b \tilde{\chi}_1^0$ and $\tilde{b}_1 \rightarrow t \tilde{chi}_1^{\pm}$, or $\tilde{t}_1 \rightarrow t \tilde{\chi}_1^0$ and $\tilde{t}_1 \rightarrow b \tilde{\chi}_1^{\pm}$, where $\tilde{\chi}_1^{\pm}$ is the lightest chargino and the mass difference $m_{\tilde{\chi}_1^{\pm}}- m_{\tilde{\chi}_1^0}$ is set to 1 GeV. No excess above the expected Standard Model background yields is observed. Exclusion limits at 95\% confidence level on the mass of the bottom squark are derived in various supersymmetric-inspired simplified models.