Search for bottom-squark pair production in $pp$ collision events at $\sqrt s = 13~$TeV with hadronically decaying tau leptons, $b$-jets and missing transverse momentum using the ATLAS detector

A search for pair production of bottom squarks in events with hadronically decaying tau leptons, $b$-tagged jets and large missing transverse momentum is presented. The analyzed dataset is based on proton$-$proton collisions at $\sqrt{s}=13$TeV delivered by the Large Hadron Collider and recorded by the ATLAS detector from 2015 to 2018, and corresponds to an integrated luminosity of 139 fb$^{-1}$. The observed data are compatible with the expected Standard Model background. Results are interpreted in a simplified model, where each bottom squark is assumed to decay to the second-lightest neutralino $\tilde \chi_2^0$ and a bottom quark, with $\tilde \chi_2^0$ decaying to a Higgs boson and the lightest neutralino $\tilde \chi_1^0$. The search focusses on final states where at least one Higgs boson decays to a pair of hadronically decaying tau leptons. This allows to significantly improve the acceptance and thus the sensitivity with respect to previous results at low masses of the $\tilde \chi_2^0$, where bottom-squark masses up to 850 GeV are excluded at the 95% confidence level, assuming a mass difference of 130 GeV between $\tilde \chi_2^0$ and $\tilde \chi_1^0$.