17. Fragmentation functions in e + e − , ep and pp collisions 1 17. FRAGMENTATION FUNCTIONS

The term ‘fragmentation functions’ is widely used for two related if conceptually different sets of functions describing final-state single particle energy distributions in hard scattering processes (see Refs. [1,2] for introductory reviews, and Refs. [3,4] for summaries of recent experimental and theoretical research in this field). The first are cross-section observables such as the functions FT,L,A(x, s) in semiinclusive e+e− annihilation at center-of-mass (CM) energy √ s via an intermediate photon or Z-boson, e+e− → γ/Z → h +X , given by