Kaonic Atom X-ray Spectroscopy: From SIDDHARTA-2 to the EXKALIBUR Program

Abstract

X-ray spectroscopy of kaonic atoms offers a unique experimental window on the interplay between low-energy strong interaction and precision atomic physics studies. This article reviews the scientific progress achieved with SIDDHARTA-2 at DAFNE and discusses how it shapes the next generation measurements. Particular emphasis is given to EXKALIBUR, a multifacility program designed to perform measurements of kaon-nucleus interactions across the periodic table and to extend kaonic atom spectroscopy toward precision tests of bound-state QED and the charged-kaon mass extraction. The first proposed strong interaction campaign at J-PARC aims to investigate kaonic atoms with solid Li, Be, and B targets using new 1-mm-thick Silicon Drift Detectors and high-resolution TES microcalorimeters, exploiting isotope pairs to isolate nuclear-structure and kaon-multinucleon effects. Measurements of Mg, Al, Si, and S with CdZnTe detectors will broaden this study toward heavier nuclei. EXKALIBUR will establish a systematic experimental framework for testing low-energy strong interaction with strangeness and bound-state QED predictions across a broad range of kaonic atoms.