Nonperturbative effects in gluon radiation and photoproduction of quark pairs

Abstract

We introduce a nonperturbative interaction for light-cone fluctuations containing quarks and gluons. Theqq interaction squeezes the transverse size of these fluctuations in the photon and one does not need to simulate this effect via effective quark masses. The strength of this interaction is fixed by data. Data on diffractive dissociation of hadrons and photons show that the nonperturbative interaction of gluons is much stronger. We fix the parameters for the nonperturbative quark-gluon interaction by data for diffractive dissociation to large masses (triple-Pomeron coupling). This allows us to predict nuclear shadowing for gluons which turns out to be not as strong as perturbative QCD predicts. We expect a delayed onset of shadowing at x ≤ 10 −2 due to the fact that photon fluctuations (containing a gluon) are heavier than in the case of quark shadowing. We use the same concept to improve our description of gluon bremsstrahlung which is related to the distribution function for a quark-gluon fluctuation and the interaction cross section of aqqG fluctuation with a nucleon. We expect the nonperturbative interaction to suppress dramatically the gluon radiation at small transverse momenta. Also the Landau-Pomeranchuk suppression for gluon radiation of a quark propagating through a nucleus turns out to be smaller than predicted by perturbative QCD.

High energy pA collisions in the color glass condensate approach II: quark pair production

“…The 3-point function is, for Gaussian correlations, the qqg-propagator and was computed in refs. [46,45,48,49]. For single quark production in the MV-model, as discussed here and by Tuchin previously, it is only these correlators that appear in the cross-section.…”

“…For this reason, no such simplification occurs for the last three terms of eq. (48). We can now write the single quark production cross-section as follows:…”

Diffraction in QCD

“…Fig. 18 shows the results of calculations [9] for gluon shadowing in lead. The expected reduction of gluon density is less than 20% even at very small x.…”

“…This size r 0 treated as a phenomenological parameter was fixed at r 0 = 0.3 fm by a fit to diffraction data [9]. Thus, we arrive at an image of the proton shown in Fig.…”

“…Since a hadron can be excited, it cannot be an eigenstate of the interaction, and can be expanded over the complete set of eigen states |α [7][8][9]:…”