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Register a new userExclusive dilepton production in ultraperipheral $PbPb$ collisions at the LHC
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In this paper we perform a systematic study of the exclusive dilepton production by $gamma gamma$ interactions in $PbPb$ collisions at the LHC Run 2 energies considering different levels of precision for the treatment of the absorptive corrections and for the nuclear form factor. The rapidity and invariant mass distributions are estimated taking into account the experimental cutoffs and a comparison with the recent ALICE and ATLAS data for the $e^+ e^-$ and $mu^+ mu^-$ production is presented.
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In this paper we investigate the production of a true muonium state, which is an atom consisting of a $mu^+ mu^-$ bound state, by $gamma gamma$ interactions in ultraperipheral $PbPb$ collisions considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The rapidity distributions and cross sections are estimated considering the RHIC, LHC and FCC energies. Our results indicate that the experimental analysis can be useful to observe, for the first time, the true muonium state.
Using the framework of collinear factorization in perturbative QCD (pQCD), we analyze the recent data of the LHCb and ALICE collaborations on exclusive photoproduction of J/{psi} in ultraperipheral pp and AA collisions, respectively. We demonstrate that the simultaneous analysis of the proton and Pb data allows us to reduce the ambiguity of the pQCD description of the $gamma p to J/psi p$ and $gamma A to J/psi p$ cross sections and, hence, to place additional constraints on the gluon distributions in the nucleon and nuclei at small x. We also make predictions for the cross section of coherent exclusive photoproduction of J/{psi} in nucleus-nucleus ultraperipheral collisions accompanied by the electromagnetic excitation of nuclei and the subsequent neutron emission.
In this paper we present a comprehensive analysis of exclusive vector meson photoproduction in $pp$, $pPb$ and $PbPb$ collisions at Run 2 LHC energies using the Color Dipole formalism. The rapidity distributions and total cross sections for the $rho$, $phi$, $J/Psi$, $Psi (2S)$ and $Upsilon$ production are estimated considering the more recent phenomenological models for the dipole - proton scattering amplitude, which are based on the Color Glass Condensate formalism and are able to describe the inclusive and exclusive $ep$ HERA data. Moreover, we also discuss the impact of the modelling of the vector meson wave functions on the predictions. The current theoretical uncertainty in the Color Dipole predictions is estimated and a comparison with the experimental results is performed.
Recent data on the nuclear modification of W and Z boson production measured by the ATLAS collaboration in PbPb collisions at $sqrt{s_{rm nn}}=5.02$ TeV show an enhancement in peripheral collisions, seemingly contradicting predictions of the Glauber model. The data were previously explained by arguing that the nucleon-nucleon cross section may be shadowed in nucleus-nucleus collisions, and hence suppressed compared to the proton-proton cross section at the same collision energy. This interpretation has quite significant consequences for the understanding of heavy-ion data, in particular in the context of the Glauber model. Instead, we provide an alternative explanation of the data by assuming that there is a mild bias present in the centrality determination of the measurement; on the size of the related systematic uncertainty. Using this assumption, we show that the data is in agreement with theoretical calculations using nuclear parton distribution functions. Finally, we speculate that the centrality dependence of the W$^-$/W$^{+}$ ratio may point to the relevance of a larger skin thickness of the Pb nucleus, which, if present, would result in a few percent larger PbPb cross section than currently accounted for in the Glauber model and may hence be the root of the centrality bias.
Using the Gribov-Glauber model for photon-nucleus scattering and a generalization of the vector meson dominance model for the hadronic structure of the photon, we make predictions for the cross section of incoherent $rho$ photoproduction in Pb-Pb ultraperipheral collisions (UPCs) in the Large Hadron Collider kinematics. We find that the effect of the inelastic nuclear shadowing is significant and leads to an additional 25% suppression of the incoherent cross section. Comparing our predictions to those of the STARlight Monte Carlo framework, we observe very significant differences.
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