Soft Parton Resummation in the Current Region of Semi-inclusive Deep Inelastic Scattering

During the past years, the H1 and ZEUS Collaborations at DESY-HERA have put a significant effort into the experimental study of semi-inclusive deep inelastic scattering (sDIS) ep → eBX . In this process, in addition to the scattered electron (or positron) e, some specific final-state hadron B, or the flow of the hadronic energy into a given region of phase space, is observed. The produced data set includes events with a large momentum transfer from the electron to the hadronic system, Q = −q ≫ ΛQCD. The theoretical description of such events can be attained with the help of methods of perturbative QCD, under the assumption of a single-photon exchange between the scattered electron and the proton. If the renormalization and factorization scales in the calculation are chosen to be of the order of the large photon virtuality Q, then the cross-section can be calculated perturbatively as a series in the small QCD coupling αs. However, the smallness of αs does not guarantee fast convergence of this series. Even when there is a large momentum scale in the collision, it is not hard to imagine a situation in which the sDIS observable receives important contributions from all orders of the perturbative expansion.