Scattering phase shift and resonance properties on the lattice: an   introduction
  We describe the method for extracting the elastic scattering phase shift from a lattice simulation at an introductory level, for non-lattice practitioners. We consider the scattering in a resonant channel, where the resulting phase shift delta(s) allows the lattice determination of the mass and the width of the resonance from a Breit-Wigner type fit. We present the method for the example of P-wave pi-pi scattering in the rho meson channel. 
S. Prelovsek, C.B. Lang, D. Mohler
hep-ph hep-lat