The Proton Structure as Measured at HERA

Abstract

In inclusive deep-inelastic scattering measurements the proton structure is usually expressed in terms of structure functions. Being observables, they depend on the measuring process. On the contrary, the proton can in theory be described in terms of Parton Density Functions (PDFs), which describe the proton universally, i.e. independently of any measuring process. The PDFs are not observables, but depend on the factorization scheme chosen, which determines how the hard scattering is separated from the non-perturbative PDFs. With a given factorization scheme, e.g. the DIS scheme, the PDFs of the proton and the hard scattering matrix element can be combined to the specific structure functions of the proton, which are subject to various measurements at HERA [1, 2].