ALICE results on vector meson photoproduction in ultra-peripheral p-Pb and Pb-Pb collisions

Lead nuclei, accelerated at the LHC, are sources of strong electromagnetic fields that can be used to measure photon-induced interactions in a new kinematic regime. These interactions can be studied in ultra-peripheral p-Pb and Pb-Pb collisions where impact parameters are larger than the sum of the nuclear radii and hadronic interactions are strongly suppressed. Heavy quarkonium photoproduction is of particular interest since it is sensitive to the gluon distribution in the target. The ALICE Collaboration has studied J/psi and psi(2S) photoproduction in ultra-peripheral Pb-Pb collisions and exclusive J/psi photoproduction off protons in ultra-peripheral p-Pb collisions at the LHC. Implications for the study of gluon density distributions and nuclear gluon shadowing are discussed. Recent ALICE results on rho photoproduction are also presented.Comment: 4 pages, 2 figures, proceedings of the International Conference on Particles and Nuclei (PANIC 2014), Hamburg, Germany, August 25-29, 201

Photoproduction of heavy vector mesons in ultra-peripheral Pb-Pb collisions

Ultra-peripheral Pb-Pb collisions, in which the two nuclei pass close to each other, but at an impact parameter greater than the sum of their radii, provide information about the initial state of nuclei. In particular, heavy vector meson production, where the particle mass sets a hard scale, proceeds in such collisions by photon-gluon interactions, and gives access to nuclear PDFs. The ALICE collaboration has published measurements of J/psi and psi(2S) photoproduction in ultra-peripheral collisions in LHC Run 1 at forward (J/psi) and mid-rapidity, and has obtained a substantially larger data set in 2015 from LHC Run 2, allowing much more detailed studies of the production mechanism to be performed. In particular, the increased energy and more detailed measurements in the forward region in Run 2 give access to significantly lower values of Bjorken-x than in previous studies. In this talk, the latest available results from Run 2 will be given.Comment: 4 pages, 5 figures, XXVIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2017

Overview of ALICE results

Selected ALICE results on the global event properties, particle spectra, azimuthal anisotropy, heavy flavour and quarkonium production in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV are presented. First results on p-Pb collisions at sqrt(s_NN) = 5.02 TeV are briefly reviewed.Comment: 5 pages, proceedings of the conference "New Trends in High Energy Physics", Alushta, Ukraine, September 23-29, 201

Evidence for nuclear gluon shadowing from the ALICE measurements of PbPb ultraperipheral exclusive J/{\psi} production

We show that the recent ALICE measurements of exclusive J/{\psi} production in ultraperipheral PbPb collisions at 2.76 TeV provide the first direct experimental evidence for the strong nuclear gluon shadowing in lead at $x \sim 10^{-3}$. The evidence is based on the comparison of the nuclear suppression factor S(x\approx 0.001)=0.61^{+0.05}_{-0.04} found in the analysis of the coherent J/{\psi} photoproduction cross sections measured by ALICE with the nuclear gluon shadowing predicted by the global fits of nuclear parton distributions and by the leading twist theory of nuclear shadowing.Comment: 14 pages, 3 figures. The final version matching the published pape