Heavy quarkonium: progress, puzzles, and opportunities

By N. Brambilla, S. Eidelman, B. Heltsley, R. Vogt, G. Bodwin, E. Eichten, A. Frawley, A. Meyer, R. Mitchell, V. Papadimitriou and 57 more. 2010

1,463 citations recorded by the source corpus.

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 hc(1P), χc2(2P), $B_{c}^{+}$, and ηb(1S). 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 $c\bar{c}$, $b\bar{b}$, and $b\bar{c}$ 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.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/dccc4d6d595318eb8731d59915498513e4743c14

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Nuclear and High Energy Physics

Citations in the corpus

Observation of X(3872) production in pp collisions at root s=7 TeV (2011, neutral): “The cross-section measurement is performed under the most favoured assumption for the quantum numbers of the X(3872) particle, J = 1 [31], which is used for the generation of Monte Carlo events.”
Heavy quarkonium in extreme conditions (2019, background): “In both cases a well defined lowest lying peak structure is visible at all separation distances r∕a ∈ [1, 17].”
Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era (2018, background): “Studies of the properties and production of quarkonia states at hadron colliders provide an important testing ground for Quantum Chromodynamics [565].”
New observables in inclusive production of quarkonia (2019, methodology): “We guide the reader to different reviews [41, 43, 338] for some specific cases, in particular that of the ψ(2S )/J/ψ yield ratio.”
Measurement of nuclear modification factors of ϒ(1S), ϒ(2S), and ϒ(3S) mesons in PbPb collisions at sNN=5.02 TeV (2018, background): “These in-medium effects have been studied in numerical simulations of quantum chromodynamics (QCD) on a space–time lattice, and captured as real and imaginary components of the heavy-quark potential [7].”
Exotics: Heavy pentaquarks and tetraquarks (2017, methodology): “The B-O approximation for QQ̄ mesons in QCD was studied by Juge, Kuti, and Morningstar [90] who investigated the hybrid bb̄g molecules, a bound system of bb̄ and excited gluon field, and also carried out detailed studies in the lattice quenched approximation.”
Excited and exotic charmonium spectroscopy from lattice QCD (2012, background): “From left to right, the operators in the left panel are (a1×D([1]) J=1), (ρ2×D [2] J=2) , (ρ×D([2]) J=2), (a0×D [3] J13=2,J=2 ), (a1×D([3]) J13=0,J=1) , (a1×D([3]) J13=2,J=1) ; the operators in”
Heavy-quark QCD exotica (2016, methodology): “Analysis preselection requirements are imposed prior to using a gradient boosted decision tree, BDTG [19], that separates the Λ0b signal from backgrounds.”