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A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B -factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau–Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h c (1 P ), χ c 2 (2 P ), , and  η b (1 S ). In addition, the unexpected and still-fascinating X (3872) has been joined by more than a dozen other charmonium- and bottomonium-like “ XYZ ” states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark–gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of , , and bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark–gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

. Open and hidden heavy-flavor physics in high-energy nuclear collisions are entering a new and exciting stage towards reaching a clearer understanding of the new experimental results with the possibility to link them directly to the advancement in lattice Quantum Chromo-Dynamics (QCD). Recent results from experiments and theoretical developments regarding open and hidden heavy-flavor dynamics have been debated at the Lorentz Workshop Tomography of the Quark-Gluon Plasma with Heavy Quarks , which was held in October 2016 in Leiden, The Netherlands. In this contribution, we summarize identified common understandings and developed strategies for the upcoming five years, which aim at achieving a profound knowledge of the dynamical properties of the quark-gluon plasma.

The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158  A  GeV In–In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2< M <2.6 GeV. The mass spectrum for M <1 GeV is consistent with a dominant contribution from π + π − → ρ → μ + μ − annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. For M >1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell–Yan pairs. The slope parameter T eff associated with the transverse momentum spectra rises with mass up to the ρ , followed by a sudden decline above. The rise for M <1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M >1 GeV and its relation to parton–hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low p T and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on ω in-medium effects.

We present a new measurement ofJ/ψproduction in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the ( J/ψ )/Drell-Yan cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the ( J/ψ )/Drell-Yan cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions.

The NA60 experiment has studied low-mass muon pair production in proton–nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the \\[\\rho /\\omega \\] and \\[\\phi \\] mesons are measured in the full \\[p_{\\mathrm {T}}\\] range accessible, from \\[p_{\\mathrm {T}}= 0\\] up to \\[2 \\, {\\hbox {GeV/c}}\\]. The nuclear dependence of the production cross sections of the \\[\\eta \\], \\[\\omega \\] and \\[\\phi \\] mesons has been found to be consistent with the power law \\[\\sigma _{\\mathrm {pA}} \\propto {\\mathrm {A}}^\\alpha \\], with the \\[\\alpha \\] parameter increasing as a function of \\[p_{\\mathrm {T}}\\] for all the particles, and an approximate hierarchy \\[\\alpha _\\eta \\approx \\alpha _\\phi > \\alpha _\\omega \\]. The cross section ratios \\[\\sigma _\\eta /\\sigma _\\omega \\], \\[\\sigma _\\rho /\\sigma _\\omega \\] and \\[\\sigma _\\phi /\\sigma _\\omega \\] have been studied as a function of the size A of the production target, and an increase of the \\[\\eta \\] and \\[\\phi \\] yields relative to the \\[\\omega \\] is observed from p–Be to p–U collisions.

We present an overview of the results obtained in pPb and PbPb collisions at the Large Hadron Collider during Run 1. We first discuss the results for global characteristics: cross sections, hadron multiplicities, azimuthal asymmetries, correlations at low transverse momentum, hadrochemistry, and femtoscopy. We then review hard and electroweak probes: particles with high transverse momentum, jets, heavy quarks, quarkonia, electroweak bosons and high transverse momentum photons, low transverse momentum photons and dileptons, and ultraperipheral collisions. We mainly focus on the experimental results, and present very briefly the main current theoretical explanations.

The study of the production of heavy quarks and quarkonia in ultra-relativistic heavy-ion collisions is crucial for our understanding of high-temperature QCD. In particular, quarkonia states are sensitive to the presence of a deconfined state, and the study of heavy quark propagation in the medium created in the collision gives important information on the attained parton density. In this paper, I will shortly review the main questions that can be addressed by the study of these hard probes, summarize the SPS and RHIC results presented at this Conference and outline possible developments in the field.

We report on the opportunities for spin physics and Transverse-Momentum Dependent distribution (TMD) studies at a future multi-purpose fixed-target experiment using the proton or lead ion LHC beams extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER@LHC using typical targets would surpass that of RHIC by more that 3 orders of magnitude in a similar energy region. In unpolarised proton-proton collisions, AFTER@LHC allows for measurements of TMDs such as the Boer-Mulders quark distributions, the distribution of unpolarised and linearly polarised gluons in unpolarised protons. Using the polarisation of hydrogen and nuclear targets, one can measure transverse single-spin asymmetries of quark and gluon sensitive probes, such as, respectively, Drell-Yan pair and quarkonium production. The fixed-target mode has the advantage to allow for measurements in the target-rapidity region, namely at large x↑ in the polarised nucleon. Overall, this allows for an ambitious spin program which we outline here.

We report a new measurement of J/ψ, ψ′ and Drell–Yan cross-sections, in the kinematical domain -0.425

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