The DEAR experiment—first results on kaonic hydrogen

The goal of the DEAR (DAΦNE exotic atom research) experiment is the precise determination of the isospin dependent antikaon-nucleon scattering lengths. The experiment accurately measures the Kα line shift and broadening, due to the strong interaction, in kaonic hydrogen and, for the first time, in kaonic deuterium. A precision measurement of kaonic hydrogen tests chiral symmetry breaking in systems with strangeness. An initial analysis of the DEAR experiment yields a shift ɛ_1s=-195±45 eV and a width Γ_1s=250±125 eV, which is more precise than the previous kaonic X-ray experiment KpX at KEK, and allows for the first time to disentangle the full pattern of the kaonic hydrogen K-series line Kα, Kβ and Kγ.