Unveiling the Invisible: ALPs and Sterile Neutrinos at the LHC and HL-LHC

TL;DR

This paper explores how mono-Higgs plus missing energy signatures at the LHC can constrain models involving axion-like particles and sterile neutrinos, providing new bounds and sensitivities for these beyond Standard Model scenarios.

Contribution

It introduces a novel analysis of mono-Higgs signatures to set bounds on ALP-Higgs and sterile neutrino-Higgs couplings at the LHC and HL-LHC, improving existing sensitivity limits.

Findings

Established bounds on ALP-Higgs coupling for masses 1-60 GeV.

Set constraints on sterile neutrino-Higgs coupling within the same mass range.

Demonstrated that ALP models have better sensitivity, especially at lower masses.

Abstract

We investigate the potential of using the signature of mono-Higgs plus large missing energies to constrain on two new physics 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 $pp \to h a a$ for ALP production and $pp \to h N N$ for sterile neutrinos at the LHC and High Luminosity LHC (HL-LHC), followed by the Higgs decay $h \to b \bar{b}$. We establish bounds on the ALP-Higgs coupling $\frac{C_{aH}}{\Lambda^2}$ and sterile neutrino-Higgs coupling $\frac{\lambda_3}{M_*}$, 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 $(\sqrt{s} = 13\;{\rm TeV}\; {\rm and}\; \mathcal{L} = 139\; {\rm fb}^{-1})$. The most stringent constraint occurs in the missing transverse energy $M_{ET}$ range $200 < M_{ET} \leq 350$ 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.