Investigating saturation effects in ultraperipheral collisions at the LHC with the color dipole model

Abstract

We investigate saturation effects in $ep$ scattering as well as in ultraperipheral $p$A and AA collisions at small $x$ with four variants of the impact parameter dependent color dipole model: with and without gluon saturation and with and without a novel mechanism that suppresses unphysical dipole radii above the confinement scale, a problem not addressed by most implementations. We show that $ep$ scattering at HERA can be very well described by any of the four variants. When going from $ep$ to $e$A scattering, saturation effects are expected to increase as $\sim$A${}^{1/3}$. In lieu of an electron-ion collider, we confront the different versions of the dipole model with data recorded in ultraperipheral collisions at the LHC in order to estimate the sensitivity of the data to gluon saturation in the target nuclei. We find that ultraperipheral PbPb collisions indicate strong saturation effects while $p$Pb collisions turn out to not have any discriminating power to distinguish saturation from non-saturation scenarios.

14 pages, 5 figures

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Cited by in corpus (16)

• Bayesian inference of the fluctuating proton shape
• Exclusive $J/\psi$ photoproduction in ultraperipheral Pb+Pb collisions at the LHC to next-to-leading order perturbative QCD
• Finite-size effects on small-$x$ evolution and saturation in proton and nuclear targets
• Observation of strong nuclear suppression in exclusive $J/\psi$ photoproduction in Au$+$Au ultra-peripheral collisions at RHIC
• The dipole cross section by the unintegrated gluon distribution at small $x$
• The unintegrated gluon distribution from the GBW and BGK models
• First measurement of the $|t|$-dependence of incoherent J/$\psi$ photonuclear production
• Exclusive $J/\psi$, $\psi (2s)$, and $e^{+}{e}^{-}$ pair production in Au$+$Au ultra-peripheral collisions at RHIC
• Beyond DGLAP improved saturation model
• Investigating saturation effects and the virtual pion in leading neutron events at HERA with the dipole model
• Complete calculation of exclusive heavy vector meson production at next-to-leading order in the dipole picture
• Geometric scaling in leading neutron events at HERA
• CGC and saturation approach: Impact-parameter dependent model of perturbative QCD and combined HERA data
• Opportunities for Imaging Light Nuclei with a Second Interaction Region at the Electron-Ion Collider
• One-to-One correspondence of soft and hard Pomeron with the CDP of the gluon density at low $x$
• Energy dependence of the proton geometry in exclusive vector meson production