Search for single vector-like quark production in the opposite-sign dilepton final state in proton-proton collisions at $\sqrt{s}=13$ TeV

Vector-like quarks are predicted in various scenarios in beyond the Standard Model (SM) theories. This work presents a search for a single vector-like top quark (T) decaying into a top quark and a SM Higgs boson (T!tH), in the T mass range from 600 GeV to 1200 GeV. The data used is from proton-proton collisions collected by the CMS experiment at the LHC in Run 2, corresponding to 138 fb 1 of integrated luminosity. The final state includes two opposite-sign leptons (muons or electrons), jets, and missing transverse momentum. The analysis uses cut-based selection criteria optimized for SM background suppression, along with a mass reconstruction algorithm developed under the neutrino kinematic assumptions. For signal extraction, the main observable is the reconstructed T mass, and the background models are data-driven. No excess in data above the standard model prediction is observed, thus upper limits are set on the production cross section of vector-like top quark times branching ratio. The analysis presents the first results for the opposite-sign dilepton final state, achieving a sensitivity similar to that of other channels with the same target.