THRESHOLD AND RESONANCE PHENOMENA IN ULTRACOLD GROUND-STATE COLLISIONS

We study the magnetic-field dependence of the cross sections for elast ic and inelastic collisions of pairs of ultracold cesium atoms in a ma gnetic trap, calculated with the coupled-channels method. We pay speci al attention to atoms in the f = 3, m(f) = - 3 weak-field seeking stat e of the lower hyperfine manifold. The cross sections show a pronounce d resonance structure. We discuss its origin, starting from the pure b ound singlet and triplet rovibrational Cs2 states and introducing pert urbations due to the hyperfine and Zeeman interactions. We also discus s the role of the centrifugal barrier in the final collision channel i n reducing the loss of atoms from the trap due to transitions induced by the magnetic dipole-dipole interaction.