Exploring the dark axion portal in the LUXE-NPOD experiment

Abstract

The optical dump at the LUXE experiment has the potential to create a large flux of $O(GeV)$ photons that can be used to look for new physics when directed at a solid material dump. The LUXE-NPOD extension of LUXE, which focuses the hard photons onto a slab of tungsten, offers two interaction points (laser-electron and photon-tungsten), making it well suited to test theories containing two or more new particles. In this paper, we examine the dark axion portal, a scenario involving both dark photons (DPs) and axionlike particles (ALPs) and their mutual interactions, and its implications on the phenomenology at LUXE-NPOD. We focus on the case of strictly massive DPs. To simulate the spectra of particle populations generated at the electron-laser interaction point, we solve a set of extended 1D cascade equations. We recover a photon spectrum consistent with previous analyses and present previously unconsidered DP and ALP spectra. Further, we derive the overall sensitivity of LUXE-NPOD to various parameters of the new particles and show that it is capable of probing potentially uncharted regions in the dark axion parameter space. For ALPs in the $10$-$500$ $MeV$ mass range, and DPs that are either heavier ($\sim GeV$) or significantly lighter $O(10^{-18}$-$10^{-13})$ $eV$, we obtain promising constraints on DP kinetic mixing parameters smaller than $10^{-2}$ and on $O(10^{-4}$-$10^{-3})$ ${GeV}^{-1}$ ALP-photon couplings. We find that restrictions on $O(10^{-3})$ kinetic mixing can be extracted for arbitrarily small DP masses. Our discussion aims to be systematic and demonstrates a practical method of analyzing constraints on multidimensional parameter spaces.