Precision measurements with kaonic atoms - from DEAR to SIDDHARTA

The final results of the DEAR (DAΦNE Exotic Atom Research) experimental program at Laboratori Nazionali di Frascati to measure the strong interaction induced shift and width of the kaonic hydrogen 1s atomic state will be presented, together with an overview of the target and detector system. The hadronic shift and width of the 1s state are sensitive observables to study quantitatively the low energy antikaon-nucIeon interaction. Proceeding to a precise determination of the isospin-dependent antikaon-nucleon scattering lengths a new detector has to be developed, namely, a Silicon Drift Detector (SDD) with good timing properties and excellent energy resolution. This new SDD system together with a kaon-trigger will suppress the x-ray background by more then two orders of magnitude compared to the DEAR case and thus will allow to measure kaonic deuterium x-rays for the first time. Kaonic hydrogen together with precision measurements of kaonic helium x-rays will allow the study of the sub-threshold Λ(1405) resonance, which might lead to strongly bound kaonic states in light nuclei. Furthermore, these precision measurements are a powerful tool to test chiral symmetry breaking in systems with strangeness. (author)