Hunting for top partner with a new signature at the LHC

Vector-like top partner plays a central role in many new physics models which attempt to address the hierarchy problem. The top partner is conventionally assumed to decay to a quark and a SM boson. However, it is also possible that the top partner decays to a non-SM scalar and a top quark. Such an exotic decay channel can be the main decay channel of top partner, and thus provides new windows to search for top partner at the LHC. In this paper, with classical machine learning method Boosted Decision Tree (BDT), we perform a model independent study of the discovery potential of this new signature at the LHC. In order to suppress the main QCD background, we consider subdominant but clean decay channel $a\to \gamma\gamma$. For completeness, the single production process and pair production process of top partner are all taken into account. We find that, for both single and pair production, the future High-Luminosity LHC can exclude the top partner mass up to TeV scale through channel $T\to t a$ ($a\to \gamma\gamma$), even if $BR(a\to \gamma\gamma)$ is as small as $\mathcal{O}$(0.1\%). Besides, our result shows that single production can overmatch pair production at 14 TeV LHC, provided that top partner is heavier than $800\sim 900$ GeV.