Direct observation of s-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 μK 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 4×10-11cm2 for atoms in the F=3, mF=0 state colliding with atoms distributed among the F=4, mF states. We also demonstrate a multiply loaded magneto-optic trap and a temperature of 1.53(7) μK.