Fano interference in quantum resonances from angle-resolved elastic scattering

Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states. Such line shapes are well known for multichannel systems, for example, in photoionization or Feshbach resonances in molecular scattering. On the other hand, in resonant single channel scattering, the signature of such interference may disappear due to the orthogonality of partial waves. Here, we show that probing the angular dependence of the cross section allows us to unveil asymmetric Fano profiles also in a single channel shape resonance. We observe a shift in the peak of the resonance profile in the elastic collisions between metastable helium and deuterium molecules with detection angle, in excellent agreement with theoretical predictions from full quantum scattering calculations. Using a model description for the partial wave interference, we can disentangle the resonant and background contributions and extract the relative phase responsible for the characteristic Fano-like profiles from our experimental measurements. Probing resonance features in a scattering process is of fundamental interest. Here the authors discuss the Fano interference due to different angular momentum components in the angle resolved scattering cross section of He*-D-2 elastic collisions.

Automated summary

The study investigates asymmetric Fano profiles in single-channel shape resonances, revealing the phenomenon through probing angular dependence. Experimental results are in excellent agreement with theoretical predictions, enabling the extraction of relative phase responsible for characteristic Fano-like profiles.