Diffractive production of vector mesons in Deep Inelastic Scattering within k_t-factorization approach

TL;DR

This work develops a comprehensive $k_t$-factorization framework for elastic vector meson production in diffractive DIS, enabling accurate description across the full $Q^2$ range from photoproduction to highly virtual regimes. Central to the approach is the unintegrated gluon structure function (DGSF) extracted from $F_{2p}$ data and embedded into a dipole-based description, with a closed-form treatment of spin-angular coupling through $S$- and $D$-wave vector meson wavefunctions. The thesis derives vector meson production amplitudes, performs twist expansions for heavy quarkonia, and carries out extensive numerical analyses showing good agreement with existing data for ground-state mesons and making distinctive predictions for excited states. The work also scrutinizes soft-hard diffusion, skewed gluon effects, and the limits of the $k_t$-factorization scheme, highlighting how hard-to-soft diffusion shapes both proton structure and diffractive vector-meson observables, and providing improved DGSF parameterizations (DGD2002) that align with recent DIS measurements. Overall, the study offers a unified, predictive framework linking proton gluon dynamics to vector-meson production across multiple channels, with implications for understanding excited-state structure and potential ambiguities in the short-distance behavior of vector meson wavefunctions.

Abstract

In this work we give a theoretical description of the elastic vector meson production in diffractive DIS developed within the k_t-factorization formalism. Since the k_t-factorization scheme does not require large values of Q^2+m_V^2, we conduct an analysis that is applicable to all values of Q^2 from photo- up to highly virtual production of vector mesons. The basic quantity in this approach -- the unintegrated gluon structure function -- was for the first time extracted from the experimental data on F_{2p}, thoroughly investigated, and consistently used in the vector meson production calculation. Moreover, by limiting ourselves to the lowest Fock state of the vector meson, we were able to construct in a closed form the theory of spin-angular coupling in the vector meson. This allowed us for the first time to address the production of a vector meson in a given spin-angular state. We performed an extensive analytical and numerical investigation of the properties of 1S, 2S, and D-wave vector meson production reactions. Treating the physical ground state vector mesons as purely 1S states, we observed a good overall agreement with all available experimental data on vector meson production. For the excited states, our analysis predicts a picture which is remarkably different from 1S-state, so that such reactions can be regarded as potential sources of new information on the structure of excited states in vector mesons.

Figures (75)

• Figure 1: Examples of deep inelastic scattering process: (a) hard DIS and (b) diffractive DIS. In the latter case $M^2_{diffr} \ll s$ and the process proceeds via pomeron $t$-channel exchange.
• Figure 2: The pQCD modeling of DIS in terms of multiproduction of parton final states.
• Figure 3: The $k_t$-factorization representation for DIS at small $x$.
• Figure 4: The Fermi-Weizsäcker-Williams diagram for calculation of the flux of equivalent photons
• Figure 5: The Fermi-Weizsäcker-Williams diagrams for calculation of the flux of equivalent photons in positronium.