DDFRG2: Double-Differential FRaGmentation model for pion production in high energy nuclear collisions

A set of Double-Differential FRaGmentation (DDFRG) models for production of fragments from nucleon–nucleus and nucleus–nucleus collisions, relevant to space radiation, is currently being developed. DDFRG1 was a previous model developed for production of protons and light ions. A new model for pion production is developed in the present work and is called DDFRG2, which is based upon thermal production of pions from a central fireball source. The Lorentz-invariant double-differential cross section is calculated in the central fireball frame, and is Lorentz transformed to the laboratory frame, which results in a closed-form analytic formula involving no numerical integration, and which can be run very efficiently in radiation transport codes. The Lorentz-invariant double-differential cross section is then integrated over angle to give the single-differential energy spectral distribution. The calculated Lorentz-invariant double-differential cross sections are compared to an extensive data set containing over 1000 data points. Agreement between model calculations and data is found to be excellent.