High precision Feshbach spectroscopy of ultracold cesium collisions

We report on the observation of multiple collision resonances in an ultraco ld cesium gas as an external magnetic field is tuned. These resonances, ass ociated with the formation of quasibound Cs-2 molecules during atomic colli sions, can be used to determine the energy structure of these molecules and the long-range binary atomic interaction parameters with high accuracy. In addition, we observe a set of much narrower collision resonances which may arise from higher-order binary scattering processes, or possibly even thre e-body Efimov states.