Quantum scattering in a juggling atomic fountain

We demonstrate a juggling atomic fountain by launching two laser-cooled bal ls of Cs-133 atoms in rapid succession. The atoms collide near the top of t he fountain and, by varying the delay between launches, we scan the collisi on energy from 19 to 150 mu K. We measure the differential scattering cross section and isolate the contributions from different partial waves includi ng their interferences. We observe the s-wave energy dependence and the p-w ave scattering threshold. We infer a triplet s-wave scattering length of -4 00a(0) and a p wave of (-107a(0))(3) for \F = 4, m = 4] + \3,3].