Parton distributions and fragmentation functions

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The parton content of nucleons and knowledge on fragmentation of final state partons are key ingredients in precision predictions at today’s particle colliders. In the standard factorization approach to QCD, they provide the essential information on the long-distance parton dynamics, which is inaccessible to perturbative computations. A central task for modern QCD theory consists of providing precision extractions of these longdistance parts (typically, parton distributions and fragmentation functions) from comparisons of experimental data with the corresponding theoretical calculations of the short-distance factors (typically, partonic cross sections) at high orders of perturbation theory. The typical accuracy of those theoretical predictions is currently at next-to-next-to-leading order (N2LO) in QCD for most cross sections of interest and even higher for fullyinclusive observables. Motivated by the theoretical progress and the available data from deep-inelastic scattering and the LHC and the prospects of the future EIC, project P2 presents a unified approach to deliver information on the non-perturbative parton dynamics at a new level of precision. To that end, it combines all efforts concerning momentum distributions of partons in the proton as well as lighter and heavier nuclei, addresses scattering processes with and without polarization, targets fragmentation functions and aims at pushing the accuracy beyond N2LO in QCD. As such, the project has numerous interrelations to all other projects, either by exploiting new results to be derived or by sharing ingredients.