Kaonic Atom Measurements with the SIDDHARTA-2 Experiment at the DA$\Phi$NE accelerator

Abstract

Kaonic atoms provide a unique experimental tool to investigate low-energy strong interactions in systems containing strangeness and, through high-lying transitions, to test bound-state quantum electrodynamics. The SIDDHARTA-2 experiment at the DA$\Phi$NE electron--positron collider performs high-precision X-ray spectroscopy of kaonic atoms using low-momentum charged kaons produced in $\phi$-meson decays. Its primary goal is the study of kaonic deuterium through the measurement of X-ray transitions to the ground state, providing direct access to the low-energy $K^-d$ interaction. In parallel, SIDDHARTA-2 has carried out a broad experimental programme with gaseous targets, including kaonic helium-4 and kaonic neon, as well as measurements of high-$n$ transitions in intermediate-mass kaonic atoms formed in the materials of the experimental setup. In this paper, the main SIDDHARTA-2 measurements and their physics motivations are reviewed, together with the experimental strategy developed for kaonic deuterium and the future perspectives of the collaboration within the EXKALIBUR programme.