Prospects for the Higgs boson self-coupling measurement with the Phase-II CMS detector upgrade using simulated pp collisions at √s = 27 TeV (High Energy LHC)

The performance of the HH->bbZZ (l) (l = e, mu) analysis is presented considering the possible High Energy upgrade of the LHC collider, at a center-of-mass energy of √s = 27 TeV and with an integrated luminosity of 15000 fb^{-1}; a comparison of the results with the same study performed in the context of the High Luminosity LHC, at a center-of-mass energy of √s =14 TeV and with an integrated luminosity of 3000 fb^{-1}, is also reported. The Phase-II upgraded CMS detector, expected in 2024, is assumed in both the scenarios. The analysis is fully based on Monte Carlo simulations: the parton-level generation of signal and backgrounds is performed with MADGRAPH5_AMC@NLO, while parton showering and hadronization are achieved with PYTHIA8; the detector response is then obtained in the parametric framework provided by DELPHES. A limit on the di-Higgs signal strength of r =1.45 is estimated at 95% CL in the inclusive bb4l channel, with a corresponding signal significance of 1.43 σ. A study on the prospects for the measurements of the Higgs self-coupling (λ_3) is also performed: the projected confidence interval on k_λ = λ_3/λ_3^{SM} is found to be [-0.7,7.2] at the 95% CL.