Bridging the divide: axion searches and axino phenomenology at colliders

Abstract

We discuss a phenomenological model that extends the minimal supersymmetric standard model to contain axions and their supersymmetric partner, the axino. In the supersymmetric DFSZ axion model, the axino has tree level couplings to the higgs sector. In the case where $R$-parity is conserved, collider experiments may be sensitive to displaced decays of heavier neutralino states into lighter, mostly axino states. We present a sensitivity analysis using a model in which mostly higgsino next-to-lightest supersymmetric particle states decay into a mostly axino lightest supersymmetric particle. The model is studied using Monte Carlo simulation produced using $\texttt{MadGraph}$ and estimates of experimental sensitivities to the model, including detector simulation and kinematic selections, are evaluated using the $\texttt{MadAnalysis5}$ framework. For a higgsino mass below 1 TeV, the axion decay constant below $f_{a} < 10^{11}$ GeV can be effectively probed by the Large Hadron Collider with an integrated luminosity of 140 fb$^{-1}$. This work demonstrates that supersymmetric DFSZ axion models can be studied with existing collider experiments, offering complementary sensitivity to direct-detection and astrophysical searches and paving the way for broader exploration of supersymmetric axion scenarios.