Coherent $$\mathrm{J}/\psi $$ and $${\uppsi '}$$ photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ TeV

The coherent photoproduction of $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ s NN = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $$\mathrm{J}/\psi $$ J / ψ is reconstructed using the dilepton ($$l^{+} l^{-}$$ l + l - ) and proton–antiproton decay channels, while for the $${\uppsi '}$$ ψ ′ the dilepton and the $$l^{+} l^{-} \pi ^{+} \pi ^{-}$$ l + l - π + π - decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 $$\mu {\mathrm{b}}^{-1}$$ μ b - 1 . The results are compared with theoretical models for coherent $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around $$6\times 10^{-4}$$ 6 × 10 - 4 , such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $$\mathrm{J}/\psi $$ J / ψ cross section including ALICE measurements at forward rapidity. The ratio of $${\uppsi '}$$ ψ ′ to $$\mathrm{J}/\psi $$ J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.

Analytical description of hadron production in hadron-hadron and nuclear-nuclear collisions in the mid-rapidity region

It is shown that the inclusive spectra of the produced hadrons in hadron-hadron and nuclear-nuclear collisions can be presented as the universal function dependent of the self-similarity parameter in the analytical form. The article gives a description of the self-similarity parameter depending on the rapidity in the mid-rapidity region. The experimental data are in good agreement with the results of our calculations in a wide energy range from a few GeV to a few TeV in the central rapidity region.

Description of ϕ-meson production in hadronic and nuclear collisions at very high energies

We expose the current experimental and theoretical situation of the interesting case of the production of [Formula: see text] mesons in up to very high energy collisions of hadrons on both nucleon and nuclear targets, and we present a quantitatively good theoretical description of the corresponding experimental data, based on the formalism of the well established Quark–Gluon String Model, that has proved to be valid for a wide energy range. All the available experimental data for [Formula: see text]-meson production in hadron–nucleon collisions on the spectra of secondary [Formula: see text], and on the ratios of [Formula: see text] and [Formula: see text] production cross-sections, as well the corresponding ones for [Formula: see text]-meson production on nuclear targets, are considered. In particular, it is seen that the production of [Formula: see text]-mesons on nuclear targets presents unusually small shadow corrections for the inclusive density in the central rapidity region.

Strangeness production in Pb-Pb collisions at LHC energies with ALICE

The results on the production of strange and multi-strange hadrons (K0S, Λ, Ξ and Ω) measured with ALICE in Pb-Pb collisions at the top LHC energy of [see formula in PDF] = 5.02 TeV are reported. Thanks to its excellent tracking and particle identification capabilities, ALICE is able to measure weakly decaying particles through the topological reconstruction of the identified hadronic decay products. Results are presented as a function of centrality and include transverse momentum spectra measured at central rapidity, pT-dependent Λ/K0S ratios and integrated yields. A systematic study of strangeness production is of fundamental importance for determining the thermal properties of the system created in ultrarelativistic heavy ion collisions. In order to study strangeness enhancement, the yields of studied particles are normalised to the corresponding measurement of pion production in the various centrality classes. The results are compared to measurements performed at lower energies, as well as to different systems and to predictions from statistical hadronization models.

Open heavy-flavour measurements with ALICE at the LHC

Heavy quarks are produced in the early stages of ultra-relativistic heavy-ion collisions, and their number is preserved throughout the subsequent evolution of the system. Therefore, they constitute ideal probes for characterising the Quark-Gluon Plasma (QGP) medium and for the study of its transport properties. In particular, heavy quarks interact with the partonic constituents of the plasma, losing energy, and are expected to be sensitive to the medium collective motion induced by its hydrodynamical evolution. In pp collisions, the measurement of heavy-flavour hadron production provides a reference for heavyion studies, and allows also testing perturbative QCD calculations in a wide range of collision energies. Similar studies in p-Pb collisions help in disentangling cold nuclear matter effects from modifications induced by the presence of a QGP medium, and are also useful to investigate the possible existence of collective phenomena also in this system. The ALICE detector provides excellent performances in terms of particle identification and vertexing capabilities. Hence, it is fully suited for the reconstruction of charmed mesons and baryons and of electrons from heavy-flavour hadron decays at central rapidity. Furthermore, the ALICE muon spectrometer allows reconstructing heavy-flavour decay muons at forward rapidity. A review of the main ALICE results on open heavy flavour production in pp, p-Pb and Pb-Pb collisions is presented. Recent, more differential measurements are also shown, including azimuthal correlations of heavy-flavour particles with charged hadrons in p-Pb collisions, and D-meson tagged-jet production in p-Pb and Pb-Pb collisions.

Nuclear modification of prompt and non-prompt J/Ψ production in p-Pb collisions at √SNN = 5.02 TeV with ALICE

Various Cold Nuclear Matter (CNM) effects, such as nuclear shadowing or partonic energy loss, can modify the production of J/Ψ in heavy-ion collisions with respect to what is measured in elementary colliding systems. The study of p-Pb collisions at the Large Hadron Collider (LHC) energy scale represents a crucial tool to assess the influence of Cold Nuclear Matter on J/Ψ production in order to achieve a more correct interpretation of Pb-Pb collision results. The ALICE detector at the LHC is capable of reconstructing J/Ψ mesons at central rapidity through their e+e- decay channel down to zero transverse momentum (pT), and has measured the fraction of J/Ψ produced from the decay of beauty-flavoured hadrons (non-prompt J/Ψ) in p-Pb collisions down to pT = 1:3 GeV/c. In this paper, the results obtained by ALICE from the measurement of the prompt and non-prompt J/Ψ yields at mid-rapidity in p-Pb collisions at √SNN = 5.02 TeV will be discussed in comparison to different theoretical predictions including CNM effects.

Transverse Momentum Distribution in Ψ(1S,2S) Photoproduction in PP and AA Collisions at the LHC

The exclusive photoproduction of the heavy vector mesons [Formula: see text] is investigated in the context of ultra-peripheral collisions proton-proton and nucleus-nucleus for the energies available at the LHC run 2. Using the light-cone color dipole formalism, it was calculated the transverse momentum distribution in the central rapidity region, in which it is expected major contribution for the process.