Search for pair production of the heavy vectorlike top partner in same-sign dilepton signature at the HL-LHC
New vectorlike quarks are predicted in many new physics scenarios beyond the Standard Model~(SM) and could potentially be discovered at the LHC. Based on a simplified model including a singlet vectorlike top partner with charge $2/3$, we investigate the process $pp \to TT$ via a $t$-channel induced by the couplings between the top partner with the first-generation SM quarks. We calculate the production cross section and further study the observability of the heavy top partner in the channel $T\to Wq$ at the high-luminosity LHC (HL-LHC) using final states with same-sign dileptons (electrons or muons), two jets, and missing transverse momentum. At the 14 TeV LHC with an integrated luminosity of 3000 fb$^{-1}$, the $2σ$ exclusion limits, as well as the $5σ$ discovery reach in the parameter plane of the two variables $g^{\ast}-R_L$, are respectively obtained at the HL-LHC. We also obtain the $2σ$ exclusion limit on the coupling strength parameter $g^{\ast}$ in the case in which the vectorlike top partner is coupled only to the first-generation quarks.