We calculate cross sections for diphoton production in (semi)exclusive PbPb collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary γγ → γγ subprocess are calculated including two different mechanisms. We take into account box diagrams with leptons and quarks in the loops. In addition, we consider a vector-meson dominance (VDM-Regge) contribution with virtual intermediate hadronic (vector-like) excitations of the photons. We get much higher cross sections in PbPb collisions than in earlier calculation from the literature. This opens a possibility to study the γγ → γγ (quasi)elastic scattering at the LHC. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS Collaborations at the LHC. We study whether a separation or identification of different components (boxes, VDM-Regge) is possible. We find that the cross section for elastic γγ scattering could be measured in the heavy-ion collisions for subprocess energies smaller than W γγ ≈ 15 − 20 GeV.

We calculate, for the first time, differential distributions for double-ρ 0 -meson production in exclusive ultraperipheral, ultrarelativistic collisions via a double-scattering mechanism. The calculations are done in impact parameter space. The cross section for γ A → ρ 0 A is parametrized based on an existing calculation. Smearing of ρ 0 masses is taken into account. The results of our calculations are compared at the Relativistic Heavy Ion Collider (RHIC) energy to the contribution of the two-photon mechanism discussed previously in the literature. The cross section for the double-scattering mechanism is found to be an order of magnitude larger at M ρρ < 2 GeV and more than two orders of magnitude at M ρρ > 3 GeV, than that for the photon-photon mechanism. Compared to the two-photon mechanism, the double-scattering mechanism populates somewhat larger ρ 0 ρ 0 invariant masses and larger rapidity distances between the two ρ 0 mesons and gives a significant contribution to the AA → AAπ + π − π + π − reaction. Some observables related to charged pions are presented too. We compare the results of our calculation with the STAR Collaboration results on four-charged-pion production. While the shape in invariant mass of the four-pion system is very similar to the measured one, the predicted cross section constitutes only 20% of the measured one. We discuss a possibility of identifying the double scattering mechanism at the Large Hadron Collider (LHC).

We calculate total and differential cross sections for J/ψ photoproduction in ultrarelativistic lead-lead collisions at the LHC energy √ s N N = 2.76 TeV. In the present approach we use a simple model based on vector dominance picture and multiple scattering of the hadronic (cc) state in a cold nucleus as an example. In our analysis we use both the classical mechanics and quantum (Glauber) formulae for calculating σ tot (J/ψP b) which is a building block of our model. We compare our UPC results with ALICE and CMS data. For semi-central collisions (b < R A + R B ) a modification of the photon flux seems necessary. We discuss different physics motivated approximations. We try to estimate the cross sections for different centrality bins and for J/ψ mesons emitted in forward rapidity range (2.5 < y < 4) corresponding to recent ALICE experimental results. Reasonable results are obtained but open questions are discussed.

The cross sections for exclusive muon-pair production in nucleus-nucleus collisions are calculated and several differential distributions are shown. Realistic (Fourier transform of charge density) charge form factors of nuclei are used and the corresponding results are compared with the cross sections calculated with monopole form factor often used in the literature and discussed recently in the context of higher-order QED corrections. Absorption effects are discussed and quantified. The cross sections obtained with realistic form factors are significantly smaller than those obtained with the monopole form factor. The effect is bigger for large muon rapidities and/or large muon transverse momenta. The predictions for the STAR and PHENIX collaboration measurements at RHIC as well as the ALICE and CMS collaborations at LHC are presented.

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