Search for the $\gamma Z$ decay mode of heavy photophobic axion-like particles at the LHC

Abstract

We assume the coupling of Axion-like particle (ALP) to diphoton $g_{a\gamma\gamma} \sim 0$ and accomplish detailed analyses for the $\gamma Z$ decay mode of such heavy photophobic ALPs at the high luminosity-Large Hadron Collider (HL-LHC). ALPs are produced with two jets via both the $s$-channel vector boson exchange and vector boson fusion processes, with the signal process $pp \to jj\, a (\to \gamma\, Z (\to \ell^+ \ell^-)\, ) $ for $\ell = e, \mu$. Signal and background events are simulated at the detector-level. Preselection criteria target events with one photon, two oppositely charged electrons or muons, and two non-$b$-tagged jets. The ALP mass is reconstructed, and kinematic observables are input into a machine learning-based multivariate analysis for optimal background rejection. Discover sensitivities on the ALP's coupling to di-$W$ boson, $g_{aWW}$, are presented in the mass range from 100 to 4000 GeV at center-of-mass energy $\sqrt{s} = 14$ TeV and integrated luminosity $\mathcal{L}=$ 3 ab$^{-1}$ and 140 fb$^{-1}$. Sensitivities on the production cross section $\sigma (pp \to jj\, a)$ times the branching ratio Br$(a \to \gamma Z)$ are also presented.