Search for pair production of gluinos decaying via top or bottom squarks in events with $b$-jets and large missing transverse momentum in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for Supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino ($\displaystyle\tilde\chi^0_1$) is reported. It uses an LHC proton--proton dataset at a center-of-mass energy $\sqrt{s} = 13$ TeV with an integrated luminosity of 14.8~fb$^{-1}$ collected with the ATLAS detector in 2015 and 2016. The signal is searched for in events containing several energetic jets, of which at least three must be identified as $b$-jets, large missing transverse momentum and, potentially, isolated electrons or muons. A topological observable formed from the mass of large-radius jets in the event is used to enhance signal discrimination. No excess is found above the predicted background. For $\displaystyle\tilde\chi^0_1$ masses below approximately 200 GeV, gluino masses of less than 1.89 TeV are excluded at the 95% CL in simplified models of the pair production of gluinos decaying via sbottom or stop. These results significantly extend the exclusion limits obtained with the 2015 only dataset.