Sensitivity to triple Higgs couplings via di-Higgs production in the 2HDM at the (HL-)LHC

Abstract

An important task of the LHC is the investigation of the Higgs-boson sector. Of particular interest is the reconstruction of the Higgs potential, i.e. the measurement of the Higgs self-couplings. Based on previous analyses, within the 2HDMs type~I and~II, we analyze several two-dimensional benchmark planes that are over large parts in agreement with all theoretical and experimental constraints. For these planes we evaluate di-Higgs production cross sections at the (HL-)LHC with a center-of-mass energy of 13 TeV at NLO in the heavy top-quark limit with the code HPAIR. We investige in particular the process $gg→hh$, with h being the Higgs boson discovered at the LHC with a mass of about 125 GeV. The top box diagram of the loop-mediated gluon fusion process into Higgs pairs interferes with the s-channel exchange of the two CP-even 2HDM Higgs bosons h and H involving the trilinear couplings λ$_{hhh}$ and λ$_{hhH}$, respectively. Depending on the size of the involved top-Yukawa and triple Higgs couplings as well as on the mass of H, the contribution of the s-channel H~diagram can be dominating or be highly suppressed. We find regions of the allowed parameter space in which the di-Higgs production cross section can differ by many standard deviations from its SM prediction, indicating possible access to deviations in λ$_{hhh}$ from the SM value λ$_{SM}$ and/or contributions involving λ$_{hhH}$. The sensitivity to λ$_{hhH}$ is further analyzed employing the mhh distributions. We demonstrate how a possible measurement of λ$_{hhH}$ depends on the various experimenal uncertainties. Depending on the underlying parameter space, the HL-LHC may have the option not only to detect beyond-the-Standard-Model triple Higgs couplings, but also to provide a first rough measurement of their sizes