Exploring vector-like top quark pair production via charged Higgs decays in multi-b-jet and opposite-sign dilepton final state at the LHC

Abstract We investigate the discovery prospects of a vector-like top partner (VLT) in the Type-II Two-Higgs-Doublet Model (2HDM-II) extended by a vector-like quark (VLQ) doublet ( TB ) at the 14 TeV Large Hadron Collider (LHC). In this work, the VLT is pair-produced via $$pp \rightarrow T\bar{T}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>p</mml:mi> <mml:mi>p</mml:mi> <mml:mo>→</mml:mo> <mml:mi>T</mml:mi> <mml:mover> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> </mml:math> and predominantly decays through the cascade $$T \rightarrow H^+ b \rightarrow t b b$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>T</mml:mi> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>H</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>b</mml:mi> <mml:mo>→</mml:mo> <mml:mi>t</mml:mi> <mml:mi>b</mml:mi> <mml:mi>b</mml:mi> </mml:mrow> </mml:math> , with the top quark decaying leptonically. The resulting final state, comprising an opposite-sign lepton pair and multiple b -jets, offers a clean experimental signature. We evaluate the discovery significance as a function of the VLT and charged Higgs masses, integrated luminosity, and background systematic uncertainties. For $$m_{H^\pm } = 600$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>m</mml:mi> <mml:msup> <mml:mi>H</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>600</mml:mn> </mml:mrow> </mml:math> GeV and 5% systematic uncertainty, a $$5\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> discovery is achievable for $$m_T \lesssim 1300$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>T</mml:mi> </mml:msub> <mml:mo>≲</mml:mo> <mml:mn>1300</mml:mn> </mml:mrow> </mml:math> GeV with 300 fb $$^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> luminosity. At higher luminosities of 1000 and 3000 fb $$^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> , the reach extends to 1500–1600 GeV, depending on the level of systematic uncertainty. While heavier $$H^\pm $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>H</mml:mi> <mml:mo>±</mml:mo> </mml:msup> </mml:math> masses reduce sensitivity, discovery remains attainable at high luminosity.