Search for non-resonant Higgs boson pair production in association with a pair of top quarks in same-sign dilepton and multilepton final states with the ATLAS detector

The exploration of Higgs boson self-coupling has remained a key focus of research since its discovery in 2012. The Higgs boson pair production in association with a top-quark pair, ttHH, is one of the rare and unexplored processes in the Standard Model (SM), with a cross-section of 0.756 (0.860) fb at 13 (13.6) TeV. Due to the strong Yukawa coupling of the top quark, ttHH is highly sensitive to potential Beyond Standard Model (BSM) physics. Additionally, it provides valuable insights into BSM interactions described by Effective Field Theories (EFTs). 

This study presents the first search for ttHH using ATLAS data, collected during LHC Run 2 and Run 3 with an integrated luminosity of 199 fb^-1. This talk focuses on ttHH decaying to the same-sign dilepton and multi-lepton final states (ttHH → SSML). We will discuss the background estimation techniques, along with a multivariate analysis approach utilizing Transformers with auxiliary tasks for signal extraction. Finally, the sensitivity of the ttHH production in the SSML channel and the combination with other channels will be presented.