Analysis of combined HERA data in the Impact-Parameter dependent Saturation model

The impact-parameter dependent saturation model (IP-Sat) is a simple dipole model that incorporates key features of the physics of gluon saturation and matches smoothly to the perturbative QCD dipole expression at large Q2 for a given x. It was previously shown that the model gives a good description of HERA data suggesting evidence for gluon saturation effects at small x. The model has also been applied to proton-proton and proton-nucleus collisions and provides the basis for the IP-Glasma model of initial conditions in heavy ion collisions. Here we present a reanalysis of available data in electron-proton collisions at small Bjorken x, including the recently released combined data from the ZEUS and H1 collaborations. We first confront the model to the high precision combined data for the reduced cross section and obtain its parameters. With these parameters fixed, we compare model results to the data for the structure function F2, the longitudinal structure function FL, the charm structure function F2cc¯, exclusive vector meson (J/ψ, ϕ and ρ) production, and deeply virtual Compton scattering. Excellent agreement is obtained for the processes considered at small x in a wide range of Q2. Our results strongly hint at universality of the IP-Sat dipole amplitude and the extracted impact-parameter distribution of the proton. They also provide a benchmark for further refinements in studies of QCD saturation at colliders.

Note:

17 pages, 18 figures

13.60.Hb
12.38.Bx
gluon: saturation
impact parameter: dependence
model: dipole
structure function: longitudinal
structure function: charm
quantum chromodynamics: perturbation theory
deeply virtual Compton scattering
DESY HERA Stor

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