Ultraperipheral collisions (UPCs) of relativistic heavy ions provide a unique laboratory for studying photon-induced reactions due to their intense photon flux. Vector mesons, such as $J/\Psi$ and $\Psi(2S)$, can be produced via $\gamma$ + A interactions, offering a powerful tool for probing the gluonic properties of the target nucleus. The $J/\Psi$ and $\Psi(2S)$ mesons introduce distinct...
The fully stripped ions used in heavy ion collisions at the LHC are an excellent source of high-energy quasi-real photons. These can interact with photons emitted by the oncoming nucleus, or with the nucleus itself, either directly in inelastic processes or diffractively via pomeron exchange. Diffractive photonuclear processes can produce exclusive vector mesons that are uniquely sensitive to...
A new phenomenon, gluon saturation, is expected to appear at high energies in QCD, where the splitting and production of gluons achieve a dynamic balance. Gluon saturation is expected to appear at lower energies in large nuclei. Due to its high sensitivity to the gluon distribution, the diffractive photoproduction of J/Ѱ is an ideal tool to search for the onset of gluon saturation.
ALICE...
The exclusive photoproduction of multi-hadron final states in ultraperipheral
collisions (UPCs) provides a unique avenue to explore quantum chromodynamics (QCD) and the nature of resonances emerging from gluonic interactions.
The ALICE Collaboration has recently performed measurements of exclusive
four-pion photoproduction, revealing data that suggest the presence of two resonances....
Diffractive vector meson production is a golden channel in the search for gluon saturation. The color glass condensate (CGC) framework has been successfully applied to describe diffractive vector meson production in $e+p$ collisions at HERA. Predictions for $\gamma+Pb$ collisions realized in ultraperipheral collisions at the LHC are however overestimating the experimental data at large center...
We study exclusive $J/\Psi$, $\Upsilon$, $b \bar{b}$ and $c \bar{c}$ photoproduction for proton and Pb targets in the high-energy limit, with the energy dependence computed using the linear Balitsky-Fadin-Kuraev-Lipatov and the nonlinear Balitsky-Kovchegov evolution equations. The difference between these two evolution equations can be directly attributed to gluon saturation physics. We find...
This talk will discuss the experimental results of ALICE, LHCb and STAR collaborations.
The photoproduction of J/Ѱ is investigated in the coherent collisions at LHC energy (√s = 5.02 TeV), for distinct transverse momentum and centrality classes: ultra-peripheral collisions (UPC) and peripheral collisions across different event geometries. An application of the convolution between the photon flux and the photonuclear cross section is explored for UPCs. In the the peripheral...
The gluon density in protons and nuclei has been observed to increase very rapidly with energy. At high energies, however, nonlinear effects of QCD start to become important, slowing down the evolution of the gluon density and hence giving rise to gluon saturation. This gluon saturation can be naturally described using the color-glass condensate (CGC) effective field theory.
In practice,...
We consider the differential cross-section for single-inclusive jet production with transverse momentum P⊥ in Deep Inelastic Scattering (DIS) at small Bjorken xBj, mediated by a virtual photon with virtuality Q2. We focus on the kinematic regime where the jet is produced in the target fragmentation hemisphere of the Breit frame, and with P⊥ ≪ Q. For a longitudinally polarised photon, we...
We predict the possibility of detecting signatures of the long-sought saturation in ultraperipheral heavy-ion collisions at currently accessible energies of the LHC. Saturation, as predicted by QCD at high energies, occurs when gluon densities in hadrons become so large that gluons begin to recombine with each other, stabilizing their population. To probe these effects, we study incoherent...
The Large Hadron Collider (LHC) has paved the way for an increasingly deeper understanding of hadronic structure. Particularly exciting is the potential to exploit the high center-of-mass energies to investigate gluon saturation in nuclei and nucleons through Ultra Peripheral Collisions (UPC).
We consider the exclusive photoproduction of a photon-pion pair, $\gamma + P \rightarrow \gamma +...
Momentum transfer distributions $d\sigma/dt$ in diffractive electroproduction of heavy quarkonia on nuclear targets are studied within a rigorous quantum-mechanical approach based on the light-front Green function formalism [1]. Such a formalism allows to include naturally the higher-twist and leading-twist shadowing corrections, as well as
the color transparency effects. Model calculations...
We present our recent results regarding the numerical solution of the
BK equation. We discuss the solution of the NLO BK equation
including the dependence on the impact parameter. We present the
obtained solutions and discuss their properties.
We also discuss solutions to the BK equation formulated in the target
rapidity and including the full impact parameter dependence.We utilise the...
Deeply Virtual Meson Production (DVMP) represents a key channel for investigating BFKL dynamics and gluon saturation within nucleons and nuclei. Describing many DVMP observables requires a treatment beyond leading power. We present a systematic framework to address next-to-leading power corrections at small-$x$, including the saturation regime, and apply it to calculate the $\gamma^{*}...
In this talk, I will focus on an interesting subclass of 2 to 3 exclusive processes, in which a pair of light mesons of large invariant mass is produced through photoproduction. These processes provide access, at leading power, to both chiral-even and chiral-odd quark generalised parton distributions (GPDs), depending on the nature and on the polarisation of the mesons. For the final-state...
I will report on our recent complete one-loop study of exclusive photoproduction of vector quarkonia off protons in Collinear Factorisation (CF) including the scale evolution of the Generalised Parton Distributions (GPDs). We have confirmed the perturbative instability of the cross section at high photon-proton-collision energies ($W_{\gamma𝑝}$) at Next-to-Leading Order (NLO) in $\alpha_s$ and...
In this talk, I will discuss a class of 2 to 3 exclusive processes which can be used to probe generalised parton distributions (GPDs). One of the main advantages of such exclusive processes is that they have an enhanced sensitivity to the x-dependence of GPDs, compared to standard 2 to 2 exclusive processes such as Deeply Virtual Compton Scattering (DVCS), which only give moment-type...
Diffractive vector meson photoproduction has long been recognized as an unparalleled probe of the gluon distribution within nuclei, potentially key to elucidating non-linear QCD effects that lead to universal states of dense gluonic matter. $\phi$ meson photoproduction is particularly useful for studying small-$x$ dynamics, especially gluon saturation, due to its sensitivity to larger dipole...
Coherent J/$\psi$ photoproduction in heavy-ion collisions has emerged as a sensitive probe of both the initial-state gluonic structure of nuclei and the dynamical electromagnetic fields generated by relativistic ions. While traditionally studied in ultra-peripheral collisions (UPCs), recent experimental observations by ALICE and STAR collaborations reveal surprising enhancements in low-$p_T$ ...
