Such particles were first identified, through their X-ray spectrum, at the KEK proton synchrotron in Tsukuba, Japan in 1997. More detailed studies have been performed at DAFNE in Frascati, Italy. Kaonic hydrogen has been created in very low energy collisions of kaons with the protons in a gaseous hydrogen target. At DAFNE, kaons are produced by the decay of φ mesons which are in turn created in collisions between electrons and positrons. The experiments analyzed X-rays from several electronic transitions in kaonic hydrogen.