Multiplet structure of Feshbach resonances in nonzero partial waves

We report a unique feature of magnetic-field Feshbach resonances in which atoms collide with nonzero orbital angular momentum. p-wave $(l=1)$ Feshbach resonances are split into two components depending on the magnitude of the resonant state's projection of orbital angular momentum onto the field axis. This splitting is due to the magnetic dipole-dipole interaction between the atoms and it offers a means to tune anisotropic interactions of an ultracold gas of atoms. Furthermore this splitting in the p-wave Feshbach resonance has been experimentally observed and is reported. A parametrization of the p-wave resonance in terms of an effective-range expansion is given.