Three-Body Recombination of Ultracold Atoms to a Weakly BoundsLevel

We discuss three-body recombination of ultracold atoms to a weakly bound s level. In this case, characterized by large and positive scattering length a for pair interaction, we find a repulsive effective potential for three-body collisions, which strongly reduces the recombination probability. In the zero temperature limit we obtain a universal relation, independent of the detailed shape of the interaction potential, for the (event) rate constant of three-body recombination: αrec0ex0ex=0ex0ex3.9a⁴/m, where m is the atom mass.