Parton Saturation Research Articles

Consequences of parton saturation and string percolation on the development of cosmic ray showers.

At high gluon or string densities, gluon saturation or the strong interaction among strings, either forming color ropes or giving rise to string percolation, induces a strong suppression in the particle multiplicities produced at high energy. This suppression implies important modifications on cosmic ray shower development. In particular, it is shown that it affects the depth of maximum, the elongation rate, and the behavior of the number of muons at energies about 10(17)--10(18) eV. The existing cosmic ray data point out in the same direction.

Parton saturation at small x and in large nuclei

Quark and gluon distributions in the light-cone wavefunction of a high energy hadron or nucleus are calculated in the saturation regime. One loop calculations are performed explicitly using the equivalence between the parton distribution in the light-cone wavefunction and the production distribution of that parton in a current-nucleon (nucleus) scattering. We argue that, except for some overall numerical factors, the Weizsäcker-Williams wavefunction correctly gives the physics of the gluon distribution in a light-cone wavefunction.

Unitarity corrections and high field strengths in high energy hard collisions

Unitarity corrections to the BFKL description of high energy hard scattering are viewed in large N c QCD in light-cone quantization. In a center of mass frame unitarity corrections to high energy hard scattering are manifestly perturbatively calculable and unrelated to questions of parton saturation. In a frame where one of the hadrons is initially at rest unitarity corrections are related to parton saturation effects and involve potential strengths A μ ∼ 1/ g. In such a frame we describe the high energy scattering in terms of the expectation value of a Wilson loop. The large potentials A μ ∼ 1/ g are shown to be pure gauge terms allowing perturbation theory to again describe unitarity corrections and parton saturation effects. Genuine nonperturbative effects only come in at energies well beyond those energies where unitarity constraints first become important.

Small- x behavior and parton saturation: A QCD model

A QCD model is defined to study questions of quark and gluon parton saturation at small x-values. The model uses a source consisting of a nucleus of heavy quarkonium bound states, states well understood in QCD. Deeply inelastic scattering, using the currents j(x) = − 1 4 F μν aF μν a and j μ(x) = ψγ μψ , is evaluated in Born and one-loop approximation in order to extract quark and gluon distributions. Quark distributions are observed to saturate while gluon distributions have a saturating and a nonsaturating component.

Virtual pair creation in a strong Bremsstrahlung field: A QED model for parton saturation

Virtual pair creation in a strong, virtual, bremsstrahlung field is considered in QED as a model for parton saturation. In a weak field the virtual pair density increases quadratically in the external field; however, at large values of the field the number density becomes independent of the strength of that field. A similar effect is found in scalar electrodynamics.