Cold collisions of ground stateHe4: GiantS-wave scattering cross sections

We have measured integral elastic cross sections for ground state ${}_{}{}^4{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He scattering at collision energies from 1.35 to 0.5 K using a novel atomic beam apparatus built into a dilution refrigerator. Scattering is almost pure s wave, and is predicted to be enormous due to a possibly bound state near the continuum. The effective integral cross section ranges from 20 to 1000 A${\mathrm{̊}}^2$ as collision energy is reduced in our experiment. These cross sections are in agreement with the values predicted using the latest analytical potential of Aziz and Slaman.