Independent Fragmentation

The independent fragmentation (IF) approach dates back to the early seventies [Krz72], and gained widespread popularity with the Field-Feynman paper [Fie78]. Subsequently, IF was the basis for two programs widely used in the early PETRA/PEP days, the Hoyer et al. [Hoy79] and the Ali et al. [Ali80] programs. PYTHIA has as (non-default) options a wide selection of independent fragmentation algorithms. The historical application of IF has been to matrix-element descriptions of jet production in $\mathrm{e}^+\mathrm{e}^-$ annihilation, i.e. for 2-, 3- and 4-parton configurations. In principle, the options made available in PYTHIA could be used for any event topology, but in practice it is strongly recommended not to use IF except for the above-mentioned case, and then only as a strawman model.