Interference effects in resonant di-Higgs production at the LHC in the Higgs singlet extension

Interference effects are well founded from the quantum mechanical viewpoint and in principle cannot be ignored in realistic studies of New Physics scenarios. In this work, we investigate the size of interference effects between resonant and non-resonant contributions to di-Higgs production in the singlet extension of the Standard Model where the additional heavy scalar provides a resonant channel of on-shell and off-shell di-Higgs production. We find these interference contributions to have a non-negligible effect on the cross-sections and differential distributions. In order to allow for an computationally efficient treatment of these effects via reweighting, we introduce a new tool utilizing a matrix-element reweighting method: HHReweighter. In addition to the broadly used invariant di-Higgs mass $m_{hh}$, we analyze the sensitivity of other kinematic variables to the interference term and propose to also use differential distributions in the Higgs transverse momentum $p_T^h$. Furthermore, we provide updates on the latest experimental and theoretical limits on the parameter space of the real singlet extension of the Standard Model Higgs sector.