An Advantage of "Upper Levels"

International audienceHadronic atoms allow, in principle, to understand hadron–nucleon interactions just below thresholds. So far, the X-ray atomic transitions have offered atomic level shifts in the “lowest” of accessible atomic states. Level broadenings have been measured directly in these states and indirectly also in higher “upper” levels. Recent experimental progress allows to find level shifts also in some upper states. Such measurements are much easier to analyse as the levels are determined essentially by a single hadron– nucleon collision at a fairly well-determined subthreshold energy. Light anti-protonic and K-mesic atoms are discussed