Searches for direct top squark pair production in compressed Supersymmetry scenarios with the ATLAS detector

In order for supersymmetry to stabilise the Higgs boson mass, the mass of the scalar partner of the top quark (the stop) is required to be below around 1 TeV. The decay of the stop is dependent on the mass difference $\Delta m = m_{\tilde{t}} - m_{\chi}$ between the stop and the lightest neutralino, assumed to be stable. For $\Delta m < m_W + m_b$ the process $\tilde{t}\rightarrow c+\tilde{\chi}$ may dominate. This poster presents a summary of stop searches targeting this region of parameter space. Conducted using a newly developed tagger for the identification of charm quarks, and using 36.5 fb${^-1}$ of proton-proton collisions collected by the ATLAS detector at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, these searches significantly extend the exclusion limits in the $(m_{\tilde{\chi}}, m_{\tilde{t}})$ parameter space made by ATLAS during Run 1 of the LHC.