# Parton Distribution Functions

## TL;DR

Parton distribution functions describe the probability of finding quarks and gluons inside protons, derived from experiments and calculable via lattice QCD, with models offering testable predictions.

## Contribution

This paper reviews the definition, experimental determination, and lattice QCD calculations of parton distribution functions, highlighting their theoretical and computational aspects.

## Key findings

- Parton distribution functions are linked to experimental scattering data.
- Integrals of these functions can be computed using lattice QCD.
- Simple models of PDFs can be tested through lattice calculations.

## Abstract

Parton distribution functions give the probability to find partons (quarks and gluons) in a hadron as a function of the fraction x of the proton's momentum carried by the parton. They are conventionally defined in terms of matrix elements of certain operators. They are determined from experimental results on short distance scattering of the partons. Integrals of these functions weighted with x^n are calculable using lattice QCD. Some simple models for their behavior have implications that could also be tested in lattice QCD.