Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering

摘要

We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calcuulated and the experimentally measured u-quark distribution up to distances of order (proportional to)2 fm in the proton rest frame. The standard calculation completely fails, however, for valence d quarks; the reasons for this discrepancy are discussed. (orig.) (ERA citation 20:011353)