Reinterpreting the ATLAS HHH$\to 6b$ Search with CheckMATE and Rivet: Validation, TRSM Benchmarks, and HL-LHC Prospects

We present an implementation in CheckMATE and Rivet of the ATLAS collaboration search for triple Higgs boson production in a six $b$-jets final state. The search relies on event selection using a deep neural network and a statistical model based on the HS3 format. Owing to a rich validation material provided by ATLAS, we perform a thorough validation of neural network input features and exclusion limits in the Standard Model and its extension with two additional singlet scalar fields (TRSM). Finally, we discuss expected performance of the search at the High Luminosity LHC in several scenarios of systematic uncertainty. We present projected exclusion limits for a set of TRSM benchmark models beyond those considered by ATLAS.