Discovery prospects of a vectorlike top partner decaying to a singlet boson

Abstract

The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or pseudoscalar has attracted some attention in the literature. We investigate the production of a weak-singlet charge-$2/3$ $T$ quark that can decay to a spinless boson ($\mathrm{\ensuremath{\Phi}}$) and a top quark at the LHC. Earlier [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, arXiv:2203.13753.], we showed that in a large part of the parameter space, the $T\ensuremath{\rightarrow}t\mathrm{\ensuremath{\Phi}}$ and the loop-induced $\mathrm{\ensuremath{\Phi}}\ensuremath{\rightarrow}gg$ decays become the dominant decay modes for these particles. Here, we investigate the discovery prospects of the $T$ quark in this region through the above decays. In particular, we focus on the $pp\ensuremath{\rightarrow}TT\ensuremath{\rightarrow}(t\mathrm{\ensuremath{\Phi}})(t\mathrm{\ensuremath{\Phi}})\ensuremath{\rightarrow}(t(gg))(t(gg))$ channel. Separating this signal from the huge Standard Model background is a challenging task, forcing us to employ a multivariate machine-learning technique. We find that the above channel can be a discovery channel of the top partner in the large part of the parameter space where the above decay chain dominates. Our analysis is largely model independent, and hence our results would be useful in a broad class of new physics models.