Partonverdelingen

Partonverdelingen, often referred to as parton distribution functions (PDFs), describe the probability of finding a specific parton—a quark or gluon—inside a proton or neutron carrying a particular fraction of the parent particle's momentum. These functions are essential in high-energy physics, especially for understanding and predicting outcomes of particle collisions in accelerators like the Large Hadron Collider.

The concept of partonverdelingen originated from the parton model proposed by Richard Feynman in the 1960s, which depicted hadrons as composed of point-like constituents called partons. PDFs are determined through experimental measurements involving deep inelastic scattering and other high-energy processes. They are not directly calculable from first principles within Quantum Chromodynamics (QCD) but are instead extracted from data using global fits within the framework of perturbative QCD.

Partonverdelingen depend on the scale of the interaction, characterized by the momentum transfer squared (Q²), due to the evolving nature of QCD interactions. This scale dependence is described by the DGLAP equations, which govern how PDFs change with energy. Typically, PDFs show that valence quarks carry a significant portion of the momentum at higher x-values (the fraction of momentum), while gluons and sea quarks dominate at lower x-values.

Accurate knowledge of partonverdelingen is crucial for predicting cross sections in particle collisions, and they are updated regularly as new experimental data become available. Several groups, such as CT (CTEQ), MMHT, and NNPDF, produce widely used PDF sets, each with different methodologies and assumptions, contributing to ongoing efforts to refine our understanding of the substructure of hadrons.