Giant Spin Relaxation of an Ultracold Cesium Gas

We have measured the rate of inelastic collisions in a cloud of doubly polarized ground-state cesium atoms ( ${F=m}_F=4\mathrm{}$) confined in a magnetic trap for temperatures $T$ between 8 and $70\mu \mathrm{K}$. We find a two-body rate coefficient varying as $T^{-0.63\mathrm{}}$. At 8 $\mu \mathrm{K}$ it reaches $4\times {10}^{-12\mathrm{}}{\mathrm{cm}}^3{\mathrm{s}}^{-1\mathrm{}}$ which is 3 orders of magnitude larger than predicted, ruling out a Bose-Einstein condensation of Cs in this internal state.