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

TL;DR

This paper investigates the potential to detect heavy photophobic axion-like particles decaying into gamma and Z bosons at the HL-LHC, using advanced simulation and machine learning techniques to improve sensitivity.

Contribution

It provides a detailed analysis of the $ ext{ALP} o ext{gamma} Z$ decay mode at the HL-LHC, including signal simulation, background rejection, and sensitivity projections for various ALP masses.

Findings

Sensitivity to ALP coupling $g_{aWW}$ for masses 100-4000 GeV.

Projected limits on production cross section times branching ratio.

Effective background suppression using machine learning.

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.