Parton distribution functions

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Parton distribution functions describe the momentum distribution of partons in hadrons.

Hadrons are made up of partons, that is, quarks and gluons. How exactly partons make up hadrons is still unclear to us because of color confinement. The precise answer to this question cannot be resolved unless we find some way of resolving nonperturbative problems in the theory of quantum chromodynamics (QCD).

However, if the hadron momentum is nearly infinite, this problem simplifys seriously. The partons can be regarded as free non-interacting particles. We only need to know the 1-dimensional momentum distribution of them for the sake of describing the hadrons. Such functions are called parton distribution functions.

Parton distribution functions are known to us in several sets worked out by different collaborations. They all use the techenics of global fit, using almost all data with different precisions and different processes. The commonly used sets includes CTEQ, GRV, MRST.