In this paper we calculate the high–energy quark–quark scattering amplitude, first in the case of scalar QCD, using Fradkin’s approach to derive the scalar quark propagator in an external gluon field and computing it in the eikonal approximation. (This approach was also recently used by Fabbrichesi, Pettorino, Veneziano and Vilkovisky to study the four–dimensional Planckian–energy scattering in...

We present the O (α s) virtual QCD corrections to gluon-gluon scattering due to the interference of tree and two-loop amplitudes. We work in conventional dimensional regularisation and give analytic expressions renormalised in the MS scheme. The structure of the infrared divergences agrees with that predicted by Catani while formulae for the finite remainder are given in terms of logarithms and...

Polarised quark distributions are extracted from semi-inclusive deep inelastic scattering data, which include the additional detection of a leading hadron to providestatisticaìàvour-tagging'. Results are combined from both proton and`neutron' targets to isolate the contributions to the nucleon spin of the individual quark avours, including the sea quarks. Spin asymmetries in the semi-inclusive ...

Nucleon-nucleon scattering at large momentum transfer is analyzed within the framework of quantum chromodynamic quark and gluon interactions. The spin dependence of the hadronic amplitude is found to be particularly sensitive to the underlying dynamical mechanisms. Detailed discussions of the quark interchange and Landshoff pinch singularity contributions are given for large angle pp, np and pi...

The scattering of charmed mesons on nucleons is investigated within a chiral quark model inspired on the QCD Hamiltonian in Coulomb gauge. The microscopic model incorporates a longitudinal Coulomb confining interaction derived from a self-consistent quasi-particle approximation to the QCD vacuum, and a traverse hyperfine interaction motivated from lattice simulations of QCD in Coulomb gauge. Fr...

The, so called, “hard-scattering approach” represents a suitable framework for the perturbative treatment of exclusive hadronic processes at large energies and (transverse) momentum transfers. In this context, diquarks can serve as a useful phenomenological concept to model nonperturbative effects which are still observable in the kinematic range accessible by present-day experiments. We outlin...

We investigate the role of nonperturbative quark-gluon dynamics in soft high energy processes. In order to reproduce differential and total cross sections for elastic protonproton and proton-antiproton-scattering at high energy and small momentum transfer it turns out that we need two scales, the gluonic correlation length and a confinement scale. We find a small gluonic correlation length, a ≃...

The photon bremsstrahlung rate from a quark jet produced in deep-inelastic scattering (DIS) off a large nucleus is studied in the collinear limit. The leading medium-enhanced higher twist corrections that describe the multiple scattering of the jet in the nucleus are re-summed to all orders of twist. The propagation of the jet in the absence of further radiative energy loss is shown to be gover...

By means of two different parametrizations of quark energy loss and the nuclear parton distributions determined only with lepton-nuclear deep inelastic scattering experimental data, a leading order phenomenological analysis is performed on the nuclear Drell-Yan differential cross section ratios as a function of the quark momentum fraction in the beam proton and target nuclei for E772 experiment...