Semi-inclusive deep inelastic scattering experiments using longitudinally polarized hydrogen (NH3) and deuterium (ND3) targets and a longitudinally polarized electron beam can be used to measure the ratio of the polarized valence quark distribution function to the unpolarized. Semi-inclusive scattering identifies an electron scattering experiment in which the scattered electron and one hadron a...

One of the most interesting consequence of non-zero intrinsic transverse momentum of partons in the nucleon is the nontrivial azimuthal dependence of the cross section of hard scattering processes. Many of the observable asymmetries contain unknown functions which provide essential information on the quark and gluon structure. Several of them have been studied in the last few years; we discuss ...

We describe the resummation of singular distributions at partonic threshold in heavy quark production, generalizing results for Drell-Yan and other electroweak hard-scattering processes.

In this contribution I discuss transverse momentum dependent quark distributions and their operator structure. Some of the experimental signatures in particular in Drell-Yan scattering are given.

Analyses of high energy elastic pp and ¯ pp scattering data from CERN ISR and SPS Collider seem to provide strong evidence in favor of the gauged nonlinear σ-model of the nucleon. This model describes the nucleon as a topological soliton and introduces the vector mesons ω, ρ, a 1 as gauge bosons. The model, however, needs to be extended to include an explicit quark sector, where left and right ...

We present the two-loop QCD helicity amplitudes for quark-gluon scattering, and for quark-antiquark annihilation into two gluons. These amplitudes are relevant for next-to-next-to-leading order corrections to (polarized) jet production at hadron colliders. We give the results in the ‘t Hooft-Veltman and four-dimensional helicity (FDH) variants of dimensional regularization. The transition rules...

We discuss corrections from the elastic limit (partonic threshold) in hadronic hard-scattering cross sections. We show why these corrections can be large at all orders in perturbation theory, and describe their resummation to arbitrary logarithmic accuracy. In particular, we discuss the role of color exchange in the hard scattering. This enables us to generalize the resummation of the Drell-Yan...

We give a complete representation of virtual Compton scattering γp → γp at large initial photon virtuality Q and small momentum transfer squared t in terms of the light-cone wavefunctions of the target proton. We verify the identities between the skewed parton distributions H(x, ζ, t) and E(x, ζ, t) which appear in deeply virtual Compton scattering and the corresponding integrands of the Dirac ...