Observability of an ultraheavy diquark decaying into vectorlike quarks at the LHC

We present a comprehensive analysis of the discovery reach and exclusion limits for an ultraheavy diquark scalar (7-9.5 TeV) decaying into a pair of vectorlike quarks (1.5-2 TeV) at the HL-LHC. Building on an improved signal selection efficiency achieved using Machine Learning techniques, we extend our previous six-jet final-state study by providing a complete likelihood-based statistical treatment of this search topology. The analysis incorporates theoretical and systematic uncertainties through nuisance parameters within the likelihood framework, enabling a consistent statistical interpretation. The mass regions of interest were determined through scans of the local $p$-values, $CL_s$, and the upper limits on the model-dependent signal strength $\mu$. The results indicate a promising sensitivity to ultraheavy diquark scalars within the explored mass range, suggesting that the HL-LHC could either discover or set stringent exclusion limits on such particles.