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

Abstract 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 ˜ 2 t ˜ 2 ⁎ or b ˜ 1 b ˜ 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 ˜ 1 t ˜ 1 ⁎ + jet , t ˜ 2 t ˜ 2 ⁎ and b ˜ 1 b ˜ 1 ⁎ , respectively.