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Cold collisions of ground state 4He: Giant S-wave scattering cross sections.

We have measured integral elastic cross sections for ground state [sup 4]He-[sup 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 [ital 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[sup 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.