
In physics, a Fano resonance, in contrast with a Breit–Wigner resonance, is a resonance for which the corresponding profile in the crosssection has the socalled Fano shape, i.e. it can be fitted with a function proportional to:
The Eres and Γres parameters are the standard Breit–Wigner parameters (position and width of the resonance, respectively). The q parameter is the socalled Fano parameter. It is interpreted (within the Feshbach–Fano partitioning theory) as the ratio between the resonant and direct (background) scattering probability. In the case the direct scattering probability is vanishing, the q parameter becomes infinite and the Fano formula is boiling down to the usual Breit–Wigner (Lorentzian) formula:
References * Ugo Fano: Phys. Rev. 124, 1866 (1961) doi:10.1103/PhysRev.124.1866 Retrieved from "http://en.wikipedia.org/" 
