Unveiling the invisible: ALPs and sterile neutrinos at the LHC and HL-LHC

We investigate the potential of using the signature of mono-Higgs plus large missing energies to constrain on two new ph ysics models, namely the model of an axion-like particle (ALP) and the model of sterile neutrinos. We focus on the Higgs-ALP interactions starting at dimension-six and the Higgs-sterile neutrino interactions starting at dimension-five, via the processes pp → haa for ALP production and pp → hNN for sterile neutrinos at the LHC and High Luminosity LHC (HL-LHC), followed by the Higgs decay \( h\to b\overline{b} \). We establish bounds on the ALP-Higgs coupling \( \frac{C_{aH}}{\Lambda^2} \) and sterile neutrino-Higgs coupling \( \frac{\lambda_3}{M_{\ast }} \), respectively, for ALP and sterile-neutrino mass ranging from 1 to 60 GeV, using the recent ATLAS data on mono-Higgs plus missing energies at the LHC (\( \sqrt{s} \) = 13 TeV and \( \mathcal{L} \) = 139 fb⁻¹). The most stringent constraint occurs in the missing transverse energy M_ET range 200 < M_ET ≤ 350 GeV. We also estimate the sensitivities that we can achieve at the HL-LHC (\( \sqrt{s} \) = 14 TeV and \( \mathcal{L} \) = 3000 fb⁻¹). We obtain improved sensitivities across various missing energy regions. The ALP model exhibits better sensitivities, particularly at lower mass range, compared to the sterile neutrino model, which shows weaker sensitivities across similar mass and energy ranges. Our results underscore the potential of the mono-Higgs signature as a robust probe for physics beyond the Standard Model.