Measurement of Cs-Cs elastic scattering atT=30 μK

We have measured the elastic collision cross section for spin polarized atomic cesium. Neutral cesium atoms are optically cooled, then loaded into a dc magnetic trap. We infer the scattering rate from the rate at which anisotropies in the initial energy distribution are observed to relax. The cross section for F=3, ${\mathit{m}}_{\mathit{F}}$=-3 on F=3, ${\mathit{m}}_{\mathit{F}}$=-3 is 1.5(4)×${10}^{\mathrm{-}12}$ ${\mathrm{cm}}^2$, and is independent of temperature from 30 to 250 μK. This determination clarifies the technical requirements for attaining Bose-Einstein condensation in a magnetically trapped Cs vapor. We also study heating due to glancing collisions with 300 K background Cs atoms.