Search for the nonresonant $\mathrm{t\bar{t}HH}$ production in the semileptonic decay of the top pair and the Higgs pair decay into b quarks at the HL-LHC

This work describes a prospective search for the production of a top quark-antiquark pair associated to a pair of Higgs bosons with the upgraded CMS detector at the High-Luminosity LHC using proton-proton collisions at $\sqrt{s}$ = 14 TeV. The analysis is performed on dedicated samples simulated with the upgraded Phase-2 conditions. The candidate $\mathrm{t\bar{t}HH}$ events are selected with criteria targeting the lepton plus jets decay channels of the $\mathrm{t\overline{t}}$ system and the decay of the double Higgs bosons into two bottom quark-antiquark pairs. In order to increase the sensitivity of the search, selected events are input to a multi-classifier deep neural network. The resulting discriminants are split into several b jet multiplicity categories with different expected signal and background rates. A simultaneous maximum likelihood fit is performed to evaluate the expected sensitivity reach. The analysis is expected to exclude $\mathrm{t\bar{t}HH}$ production down to 3.14 times the SM cross section with 3000 fb$^{-1}$ of data. The sensitivity for Minimal Composite Higgs Model scenarios is also presented.