ATLAS sensitivity to dark matter produced in association with heavy quarks at the HL-LHC

This note presents the prospects of a search for weakly interacting dark matter produced in association with heavy flavour quarks at the HL--LHC. The search is performed assuming 3000$~\text{fb}^{-1}$ of proton-proton collisions collected by the ATLAS detector at a centre of mass energy of $14~\text{ TeV}$. Two experimental signatures are investigated, characterised by missing transverse momentum and either a pair of bottom quarks or two opposite-charge leptons (electrons or muons) resulting from the decay of a top quark pair or a top quark and a $W$-boson. The results are interpreted within the framework of Simplified Models which couple the dark and Standard Model sectors via the exchange of colour-neutral spin-0 mediators, assuming unitary couplings and a dark matter mass of $1~\text{GeV}$. Compared to a previous search conducted with $36.1~\text{fb}^{-1}$ of data at $\sqrt{s}=13~\text{ TeV}$, the reach achievable for dark matter detection in events with bottom quarks is extended by a factor of 3--8.7 following the increased luminosity and centre of mass energy expected for the HL--LHC final dataset, along with the upgrades to the ATLAS detector. For events with top quarks in the final state, the expected sensitivity to scalar mediator production extents by a factor of 5, and exclusion of pseudoscalar mediator masses up to $385~\text{GeV}$ becomes possible.