Main Question or Discussion Point
What is the true concept of resonance in particle physics? can particle production happen via resonance? how?
Typically, such a resonance peak is accompanied by a pole of the associated green's function in the nonphysical sheet, a complex number whose real part defines the resonance energy, and whose imaginary part denotes (up to a constant factor) the decay rate of an associated unstable particle.Now if this scattering probability increases strongly at or near a certain energy, then one speaks of a resonance. A possible mechanism (but not the only one) for a resonance is the intermediate formation of a compound particle which decays again after some time, setting free again the scattering particles (or other ones).