Asymptotic gluon density within the color dipole picture in light of HERA high-precision data

Abstract

We present an analysis of the most precise set of Hadron-Electron Ring Accelerator (HERA) data within the color dipole formalism, by using an analytical gluon density, based on the double-logarithm approximation of the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) equations in the asymptotic limit of the scaling variable, σ ¼ log ð1=xÞlog ðlog ðQ2=Q2 0ÞÞ → ∞. Fits to the data, including charm and bottom quarks, are performed and demonstrate the efficiency of the model in describing the reduced cross section, σr, in the wide range Q2∶ ð1.5; 500Þ GeV2 for two dipole models including parton saturation effects. We also give predictions to Fcc¯ 2 , Fbb¯ 2 and FL, all describing the data reasonably well in the range Q2∶ ð2.5; 120Þ GeV2. Total cross sections of exclusive photoproduction of J=ψ and ρ are also calculated and successfully compared to HERA data and recent measurements at LHCb.