2025/09/23 by Frost, James, Pacey, Holly, Dingley, Thomas Benjamin
paper · doi:10.17181/hx7h0-8zs64
A feasibility study of triple Higgs boson production at the Future Circular Collider proton-proton stage, FCC-hh, at a centre-of-mass energy √(s)=84 TeV has been performed in the 4b2τ final state. SM-like HHH signals are studied. Both the mixed leptonic-hadronic (τlepτhad) and fully hadronic (τhadτhad) decay modes of the τ-lepton pair are considered in orthogonal channels and combined. For each channel, a neural network classifier is trained to improve experimental sensitivity and discriminate between the HHH signals and Standard Model backgrounds, utilising kinematic features from the reconstructed objects and Higgs boson candidates in the events. Considering a conservative jet flavour identification uncertainty (uncertainty Scenario I), a 95% upper cross-section limit of 3 × σHHHSM is expected, with comparable sensitivity between the two analysis channels. The sensitivity of this final state to constrain the tri-linear and quartic Higgs self-couplings is evaluated for several uncertainty scenarios. Assuming the SM value of the trilinear self-coupling, a constraint is derived on the quartic self-coupling of between -5.6 and 21 times the SM value at 68% CL. In combination with other triple-Higgs final states, this result demonstrates the potential of the FCC-hh to constrain the quartic Higgs self-coupling.