What exactly is a parton density?

John C. Collins

Research output: Contribution to journalArticlepeer-review

226 Scopus citations


I give an account of the definitions of parton densities, both the conventional ones, integrated over parton transverse momentum, and unintegrated transverse-momentum-dependent densities. The aim is to get a precise and correct definition of a parton density as the target expectation value of a suitable quantum mechanical operator, so that a clear connection to non-perturbative QCD is provided. Starting from the intuitive ideas in the parton model that predate QCD, we will see how the simplest operator definitions suffer from divergences. Corrections to the definition are needed to eliminate the divergences. An improved definition of unintegrated parton densities is proposed.

Original languageEnglish (US)
Pages (from-to)3103-3120
Number of pages18
JournalActa Physica Polonica B
Issue number6
StatePublished - Jun 1 2003

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)


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