Probing open- And closed-channel -wave resonances

We study the near-threshold molecular and collisional physics of a strong -wave Feshbach resonance through a combination of measurements, numerical calculations, and modeling. Dimer spectroscopy employs both radio-frequency spin-flip association in the MHz band and resonant association in the kHz band. Systematic uncertainty in the measured binding energy is reduced by a model that includes both the Franck-Condon overlap amplitude and inhomogeneous broadening. Coupled-channels calculations based on mass-scaled potentials compare well to the observed binding energies and also reveal a low-energy -wave shape resonance in the open channel. Contrary to conventional expectation, we observe a nonlinear variation of the binding energy with magnetic field, and explain how this arises from the interplay of the closed-channel ramping state with the near-threshold shape resonance in the open channel. We develop an analytic two-channel model that includes both resonances as well as the dipole-dipole interactions which, we show, become important at low energy. Using this parametrization of the energy dependence of the scattering phase, we can classify the studied resonance as broad. Throughout the paper, we compare to the well-understood -wave case and discuss the significant role played by van der Waals physics. The resulting understanding of the dimer physics of -wave resonances provides a solid foundation for future exploration of few- and many-body orbital physics.