text: The Sanford–Wang parameterisation is an empirical formula used to model the production of pions in nuclear interaction of the form p+A → +X where a beam of high-energy protons hit a material.
  Its formula for the double-differential cross section with respect to momentum (p) and solid angle () is as follows.
  Where p and  are the momentum of the outgoing pion and its angle from the direction of the incident proton.  The numbers  are the Sanford-Wang parameters and are typically varied to give a good fit with experimental data.