Hadron structure at small-x via unintegrated gluon densities

TL;DR

This paper reviews the formalism and models of unintegrated gluon distributions at small-x, emphasizing their role in describing proton structure through high-energy factorization and recent phenomenological analyses.

Contribution

It provides a comprehensive review of UGD formalism within the BFKL approach, introduces various models, and discusses recent phenomenological studies at small-x.

Findings

Validation of HEF in diffractive  production

Sensitivity of polarized cross sections to meson transverse momenta

Overview of UGD models and their phenomenological applications

Abstract

Inclusive as well as exclusive emissions in forward and central directions of rapidity are widely recognized as excellent channels to access the proton structure at small-x. In this regime, to describe nucleons structure, it is necessary to use kT-unintegrated distributions. In particular, at large transverse momenta, the x-evolution of the so-called unintegrated gluon distribution is driven by the Balitsky-Fadin-Kuraev-Lipatov equation, within the framework of the high-energy factorization (HEF). Recent analyses on the diffractive electroproduction of \rho mesons have corroborated the underlying assumption that the small-size dipole scattering mechanism is at work, thus validating the use of the HEF formalism. Nonetheless, a significant sensitivity of polarized cross sections to intermediate values of the meson transverse momenta, where, in the case of inclusive emissions, a description at the hand of the transverse momentum dependent (TMD) factorization starts to be the most appropriate framework, has been observed. In this work, we will review the formal description of the UGD within the BFKL approach and present some UGD models that have been proposed, then we will describe the state of the art of some recent phenomenological analyses.