Exploring the dark axion portal in the LUXE-NPOD experiment

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 ( ∼ 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.