Heavy-flavour and quarkonium production in the LHC era: from proton-proton to heavy-ion collisions.

This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the proton and nucleus structure at high energy to deconfinement and the properties of the Quark-Gluon Plasma. Emphasis is given to the lessons learnt from LHC Run 1 results, which are reviewed in a global picture with the results from SPS and RHIC at lower energies, as well as to the questions to be addressed in the future. The report covers heavy flavour and quarkonium production in proton-proton, proton-nucleus and nucleus-nucleus collisions. This includes discussion of the effects of hot and cold strongly interacting matter, quarkonium photoproduction in nucleus-nucleus collisions and perspectives on the study of heavy flavour and quarkonium with upgrades of existing experiments and new experiments. The report results from the activity of the SaporeGravis network of the I3 Hadron Physics programme of the European Union 7[Formula: see text] Framework Programme.

Cronin effect in hadron production off nuclei.

Recent data from RHIC for high- pT hadrons raised again the long-standing problem of quantitatively understanding the Cronin effect, i.e., nuclear enhancement of high- pT hadrons. All existing models for the Cronin effect rely on a fit to the data to be explained. We develop a phenomenological description based on the light-cone QCD-dipole approach which allows one to explain data without fitting to them and to provide predictions for pA collisions at RHIC and LHC. We point out that the underlying mechanism drastically changes with energy, from incoherent production of high- pT hadrons on different nucleons at low energies, to an entirely coherent process at very high energies.

Scanning the quark-gluon plasma with charmonium.

We suggest the variation of charmonium production rate with Feynman x(F) in heavy ion collisions as a novel and sensitive probe for the properties of the created matter. Final state interactions with the comoving matter create a minimum at x(F) = 0, which is especially deep and narrow if a quark-gluon plasma is formed. While a strong effect is predicted at SPS, at the RHIC energy it overlaps with the expected peak formed by shadowing effects and needs comparison with pA data. We predict a steep dependence on centrality and suggest that this new probe is complementary to the dependence on transverse energy, and is more sensitive to a scenario of final state interactions.

Energy loss of fast quarks in nuclei.

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of 2H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is -dE/dz = 2.32+/-0.52+/-0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.

Nonperturbative gluon radiation and energy dependence of elastic scattering.

The energy dependence of the total hadronic cross sections is caused by gluon bremsstrahlung which we treat nonperturbatively. It is located at small transverse distances about 0.3 fm from the valence quarks. The cross section of gluon radiation is predicted to exponentiate and rise with energy as s(delta) with delta = 0.17+/-0. 01. The total cross section also includes a large energy independent Born term which corresponds to no gluon radiation. The calculated total cross section and the slope of elastic scattering are in good agreement with the data.