Prospects for Dark Matter searches in mono-photon and VBF+$E_T^{miss}$ final states in ATLAS

This document presents a prospect study for dark matter searches with the ATLAS detector at luminosities as expected at HL-LHC. A scenario where the Standard Model is extended by the addition of an electroweak fermionic triplet with null hyper charge is considered. The lightest mass state of the triplet constitutes a weakly interacting massive particle dark matter candidate. This model is inspired by Supersymmetry and by the Minimal Dark Matter setup, and provides a benchmark in the spirit of simplified models. Projections for an integrated luminosity of 3000 fb$^{−1}$ are presented for the dark matter searches in the mono-photon and VBF+$E_{T}^{miss}$ final states, based on the run-2 analyses strategy. To illustrate the experimental challenges associated to a high pile-up environment due to the high luminosity, the VBF+$E_{T}^{miss}$ topology is considered and the effect of the increased pile-up on the VBF invisibly decaying Higgs boson is studied as a benchmark process.