Executive Summary : | The HERA experiments measuring Deep Inelastic Scattering (DIS) in ep collisions provide precise measurements of proton structure functions and confirm the Dipole Picture (DGLAP). The DGLAP evolution provides the most complete understanding of hadronic structure, revealing the densities of valence quarks, sea quarks, and gluons in the proton and their distribution in resolution parameter Q2 and momentum fraction parameter x. However, this picture is incomplete due to contradictions in gluon cross sections exceeding total proton cross sections and many interactions at HERA being diffractive. The Dipole Picture solves these issues by providing a natural mechanism for gluon saturation and a unified description of diffractive and non-diffractive DIS. In 2006, a version of the dipole model was developed, which treats proton geometry in two ways: the longitudinal part of the proton is described in momentum space (DGLAP), and the transverse part is modelled in coordinate space. This opens up new frontiers in our understanding of the proton and allows for direct measurement of Mandelstam t-variable and gluon fluctuations in "incoherent" events.
In 2016, the "hotspot model" was published, a non-perturbative model of gluon fluctuations that can describe some existing data. The researchers plan to use the hotspot model as a starting point and develop a perturbative approach to the transverse gluon structure of the proton, equivalent to the DGLAP evolution but in coordinate space. This will allow for a natural mechanism for gluon saturation and significantly extend the phase-space for the transverse structure of the proton. |