Multiparton distribution functions in quantum chromodynamics

The structure of hadrons (protons) and the dynamics of their interaction are usually studied in collisional experiments by exploring hard single parton–parton scattering described in terms of structure functions (single-particle distributions). Completely new and unique information comes from the selection and analysis of events in which two (or more) hard parton scatterings concurrently occur in a single $\bar {\rm p}{\rm p}$ (Tevatron; FermiLab, USA) or pp (LHC; CERN, Switzerland) collision. The simulation of such double (multiple) parton scatterings involves two-parton (multiparton) distribution functions. Properties of these functions, which may be extracted from quantum chromodynamics, are reviewed.