  We report on experiments investigating the collisional properties of atoms at
ultralow collision energies using an all-optical atom collider. By using a pair
of optical tweezers, we can manipulate two ultracold atom clouds and collide
them together at energies up to three orders of magnitude larger than their
thermal energy. Our experiments measure the scattering of $\rm ^{87}Rb$, $\rm
^{40}K$, and $\rm ^{40}K$-$\rm ^{87}Rb$ collisions. The versatility of our
collider allows us to probe both shape resonances and Feshbach resonances in
any partial wave. As examples, we present experiments demonstrating p-wave
scattering with indistinguishable fermions, inelastic scattering at non-zero
energies near a homonuclear Feshbach resonance, and partial wave interference
in heteronuclear collisions.
