Direct Observation ofs-Wave Atomic Collisions

We observe the angular distribution of $s$-wave scattering of Cs atoms in an atomic fountain by selecting and probing atomic velocities. At an average temperature of $T=0.89\mathrm{}$ $\mu$K the scattering is predominantly $s$-wave and we have a sensitivity to $p$-wave cross sections as small as 0.1% of the $s$-wave. The cross section is $4\times {10}^{-11\mathrm{}}{\mathrm{cm}}^2$ for atoms in the $F=3\mathrm{}$, $m_F=0\mathrm{}$ state colliding with atoms distributed among the $F=4\mathrm{}$, $m_F$ states. We also demonstrate a multiply loaded magneto-optic trap and a temperature of 1.53(7) $\mu$K.