Probing Higgs portals with matrix-element based kinematic discriminants in ZZ → 4ℓ production

Abstract

A Higgs portal in the form of the operator |H|2 provides a minimal and theoretically motivated link between the Standard Model (SM) and new physics. While Higgs portals can be constrained well by exotic Higgs decays if the beyond-the-SM states are light, testing scenarios where these particles are kinematically inaccessible is known to be challenging. We explore the sensitivity of future hadron collider measurements of ZZ → 4ℓ production in constraining Higgs portal interactions. It is shown that by using a matrix-element based kinematic discriminant the reach of the high-luminosity option of the Large Hadron Collider (LHC) can be significantly enhanced compared to studies that are based on measurements of the four-lepton invariant mass spectrum alone. We also analyse the potential of the high-energy upgrade of the LHC and a Future Circular Collider in constraining new physics that couples to |H|2. The obtained constraints are compared to the limits one expects to find from other single-Higgs probes. In addition, we provide an independent analysis of the relevant Higgs portal effects in double-Higgs production. We find that the constraints obtained from our ZZ → 4ℓ analysis turn out to be both competitive with and complementary to the projected limits obtained using other search techniques.