Probing stops in the coannihilation region at the HL-LHC: A comparative study of different processes

In the minimal supersymmetric model, the coannihilation of the lighter stop t˜₁ and bino-like dark matter χ provides a feasible way to accommodate the correct dark matter relic abundance. In this scenario, due to the compressed masses, t˜₁ merely appears as missing energy at the LHC and thus the pair production of t˜₁ can only be probed by requiring an associated energetic jet. Meanwhile, since t˜₂ and b˜₁ are correlated in mass and mixing with t˜₁, the production of t˜₂t˜₂^⁎ or b˜₁b˜₁^⁎, each of which dominantly decays into t˜₁ plus Z, h or W boson, may serve as a complementary probe. We examine all these processes at the HL-LHC and find that the 2σ sensitivity to χ mass can be as large as about 570 GeV, 600 GeV for m_t˜2≲1100 GeV and 1.1 TeV for m_b˜1≲1375 GeV from the production process of t˜₁t˜₁^⁎+jet, t˜₂t˜₂^⁎ and b˜₁b˜₁^⁎, respectively.