Strong electromagnetic field arising from the Lorentz-contraction and a large number of charges (Z) in the colliding nuclei at ultrarelativistic speeds can generate a large flux of quasi-real photons. Consequent photon-induced interactions could reasonably explain the observed enhancements of $J/\psi$ and $e^{+}e^{-}$ pair productions at very low transverse momenta ($p_{T}$) in peripheral...
Recently, significant enhancements of $e^{+}e^{-}$ pairs at very low transverse momentum ($p_{T}$) were observed by the STAR collaboration in peripheral Au+Au collisions. The excess can be explained by photon-photon interactions induced by the extremely strong electromagnetic field produced by the fast-moving heavy ions. These photon-photon interactions could provide a novel probe to the...
The ALICE experiment has significantly upgraded its detectors. It will make possible to perform new measurements in the Ultra Peripheral Collisions (UPCs) of lead nuclei for the integrated luminosity of $\mathcal{L}^{\rm Pb-Pb}=13$/nb during Run 3 and Run 4. For Run 5 and beyond, a completely new next-generation heavy-ion experiment ALICE 3 is proposed. The new detector system will cover
much...
The photon-photon interaction in ultra-relativistic heavy-ion collision is a source of the $(e^+,e^-)$ pairs. The photon-photon fusion leads to the lepton creation in the broad configuration space around ''collision'' point. Those created close to heavy nuclei may undergo strong interaction with them.
The impact parameter space distributions of electrons and positrons are calculated within...
We present a study of photon-photon scattering in the mass range $W_{\gamma \gamma}<5$ GeV. We extend earlier calculations of this cross section for $W_{\gamma \gamma}>5$~GeV into the low mass range where photoproduction of the pseudoscalar resonances $\eta$, $\eta'(958)$ contributes to two-photon final states. We present the elementary photon-photon cross section as a function of diphoton...
The lepton pair production in ultraperipheral collisions is studied in the classical field approximation. We derive a general form of the cross section in terms of photon distributions that depend on the transverse momentum and coordinate based on the wave packet form of nuclear wave functions. Such a general form of the cross section in the classical field approximation contains the results...
We present the latest predictions for several QCD processes at low-x in the color dipole picture which are of interest for current hadron-hadron and future electron-hadron colliders. The predictions are derived using the solution to the Balitsky-Kovchegov equation for proton and nuclear targets with the collinearly improved kernel and including the impact-parameter dependence. Two different...
We present, for the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both pomeron-lead and pomeron-proton topologies. The analysis is performed over 10.4 units of pseudorapidity at a nucleon-nucleon center-of-mass energy of 8.16 TeV, i.e. almost 300 times higher than previous measurements of diffractive production in proton-nucleus collisions. For...
In heavy-ion collisions, the highly relativistic ions act as a strong source of electromagnetic radiation, enhanced by the large proton charge number $Z$. Ultra-peripheral collisions (UPC) offer a natural environment in which to observe the photon-initiated production of Beyond Standard Model (BSM) processes with QED couplings. One such process sensitive to BSM effects is light-by-light...
The LHCb detector is a single-arm forward spectrometer covering the pseudorapidity range 2 < 𝜂 < 5, designed for the study of particles containing bottom or charm quark. The study of exclusive vector meson photoproduction in ultra-peripheral lead-lead collisions is essential to understand physics at low Bjorken x. In particular, coherent J/ψ and ψ(2S) mesons are promising probes of nuclear...
We discuss the role of $c \bar c g$-Fock states in the diffractive photoproduction of J/ψ-mesons on heavy nuclei. We build on our earlier description of the process in the color-dipole approach, where we took into account the rescattering of $c \bar c$ pairs using a Glauber-Gribov form of the dipole-nucleus amplitude. The results of our calculations are compared to recent data on the...
The PHENIX experiment was operated at BNL-RHIC which collides heavy ions at
relativistic energy to create a quark-gluon plasma (QGP), in which quarks and gluons are deconfined. It is well known that the QGP produced in heavy ion collisions exhibits collective motion. In recent years, similar collective effect have been discovered in small systems at high energy collisions. This result...
Photonuclear collisions are one of the simplest processes that can happen in a heavy-ion collision. They occur when one nucleus emits a quasi-real photon which interacts with the other colliding nucleus, similar to an $e+A$ collision except that the photon tends to have a much smaller virtuality. Photonuclear collisions can be used to study bulk properties of the medium such as collectivity...
Since 2011 a wide variety of measurements suggest the existence of strong collectivity in collisions of small systems such as proton-proton (pp) and proton-nucleus (pPb) with hydrodynamic models and gluon saturation in the initial state as two theory alternatives showing consistency with the observations. These results raise the question as to whether such phenomena may be present in even...
