  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.
