Exotic atom research at DAΦNE (The DEAR Experiment)

The DEAR experiment (DEAR:DAΦNE Exotic Atom Research) is presented. Reliable data, in terms of high statistics, low background, good resolution, as it is possible to obtain with DEAR from kaonic hydrogen and kaonic deuterium, will allow to make the first precision measurement of the kaon-nucleon scattering length aK-n. The measurement will allow to understand the kaon-nucleon interaction, in particular by definitely solving the 'kaonic hydrogen puzzle' and to study the nature of the Λ(1405) (K bar N bound state or an elementary three-quark state ?). The KN scattering length is related to an important quantity such as the KN sigma term. As in the case of the πN sigma term, one can eventually extract the KN sigma term from accurate KN interaction data at threshold. At present, this is not possible. The KN sigma term is present in the nucleon mass and its value allows to estimate the amount of the nucleon mass due to strangeness. The KN sigma term is encountered also in describing kaon condensation in dense nuclear matter and, consequently it can give independent information with respect to the phenomena observed in relativistic heavy ion collisions. (authors)