Photoproduction of vector mesons: from ultraperipheral to semi-central heavy ion collisions

We discuss nuclear cross sections for $AA \to AAV$ and $AA \to AAVV$ reactions with one or two vector mesons in the final state. Our analysis is done in the impact parameter space equivalent photon approximation. This approach allows to consider the above processes taking into account distance between colliding nuclei. We consider both ultraperipheral and semi-central collisions. We are a first group which undertook a study of single $J/\psi$ photoproduction for different centrality bins. We show that one can describe new ALICE experimental data by including geometrical effects of collisions in the flux factor. Next, total and differential cross section for double-scattering mechanism in the exclusive $AA \to AAVV$ reaction in ultrarelativistic ultraperipheral heavy ion collisions is presented. In this context we consider double photoproduction and photon-photon processes. Simultaneously, we get very good agreement of our results with STAR (RHIC), CMS and ALICE (LHC) experimental data for single $\rho^0$ and $J/\psi$ vector meson production. A comparison of our predictions for exclusive four charged pions production is also presented.Comment: 6 pages, 6 figures, an invited talk presented by M. Klusek-Gawenda at the 14th International Workshop on Meson Production, Properties and Interaction, (Meson2016), Krakow, Poland, June 2-7, 201

Light-by-light scattering in ultraperipheral collisions of heavy ions with future FoCal and ALICE 3 detectors

We discuss possible future studies of photon-photon (light-by-light) scattering using a planned FoCal and ALICE 3 detectors. We include different mechanisms of $\gamma\gamma\to\gamma\gamma$ scattering, such as double-hadronic photon fluctuations, $t/u$-channel neutral pion exchange or resonance excitations ($\gamma \gamma \to R$) and deexcitation ($R \to \gamma \gamma$). The broad range of (pseudo)rapidities and lower cuts on transverse momenta open a necessity to consider not only dominant box contributions but also other subleading contributions. Here we include low mass resonant $R = \pi^0$, $\eta$, $\eta'$ contributions. The resonance contributions give intermediate photon transverse momenta. However, these contributions can be eliminated by imposing windows on di-photon invariant mass. We study and quantify individual box contributions (leptonic, quarkish). The electron/positron boxes dominate at low $M_{\gamma \gamma}<1$ GeV di-photon invariant masses. The PbPb$\to$PbPb$\gamma \gamma$ cross section is calculated within equivalent photon approximation in the impact parameter space. Several differential distributions are presented and discussed. We consider four different kinematic regions. We predict cross section in the (mb-b) range for typical ALICE 3 cuts, a few orders of magnitude larger than for the current ATLAS or CMS experiments. We also consider the two-$\pi^0$ background which can, in principle, be eliminated at the new kinematical range for the ALICE 3 measurements by imposing dedicated cuts on di-photon transverse momentum and\or so-called vector asymmetry.Comment: 20 pages, 19 Figures, 3 Tables; misprint corrected, 1 figure adde

Double-photon exclusive processes with heavy-quark–heavy-antiquark pairs in high-energy Pb-Pb collisions at energies available at the CERN Large Hadron Collider

The cross section for exclusive heavy-quark and heavy-antiquark pair (Q¯Q) production in peripheral ultrarelativistic heavy-ion collisions is calculated at an energy available at the CERN Large Hadron Collider, i.e., √ sNN = 5.5 TeV. Here we consider only processes with photon-photon interactions and omit diffractive contributions. We present results in the impact parameter equivalent photon approximation and compare some of them with results obtained by exact calculations of the Feynman diagrams in the momentum space.We include Q¯Q, Q¯Qg, and Q¯Qq¯q final states as well as photon single-resolved components. Realistic charge densities in nuclei were taken in the calculation. The different components give contributions of the same order of magnitude to the nuclear cross section. The cross sections found here are smaller than those for the diffractive photon-Pomeron mechanism and larger than the diffractive Pomeron-Pomeron discussed in the literature

Double-photon exclusive processes with heavy-quark–heavy-antiquark pairs in high-energy Pb-Pb collisions at energies available at the CERN Large Hadron Collider

The cross section for exclusive heavy-quark and heavy-antiquark pair (Q¯Q) production in peripheral ultrarelativistic heavy-ion collisions is calculated at an energy available at the CERN Large Hadron Collider, i.e., √ sNN = 5.5 TeV. Here we consider only processes with photon-photon interactions and omit diffractive contributions. We present results in the impact parameter equivalent photon approximation and compare some of them with results obtained by exact calculations of the Feynman diagrams in the momentum space.We include Q¯Q, Q¯Qg, and Q¯Qq¯q final states as well as photon single-resolved components. Realistic charge densities in nuclei were taken in the calculation. The different components give contributions of the same order of magnitude to the nuclear cross section. The cross sections found here are smaller than those for the diffractive photon-Pomeron mechanism and larger than the diffractive Pomeron-Pomeron discussed in the literature