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We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on J / ψ and ψ (2 S) mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from feeddown from bottom hadron decays. For our predictions for ψ (2 S) production, the mechanism of sequential regeneration relative to the more strongly bound J / ψ meson plays an important role in interpreting recent ALICE data. [ABSTRACT FROM AUTHOR]

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of π 0 , η , and η ′ , and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions. [ABSTRACT FROM AUTHOR]

Heavy and light quarks produced in high- p T partonic collisions radiate differently. Heavy quarks regenerate their color field, stripped-off in the hard reaction, much faster than the light ones and radiate a significantly smaller fraction of the initial quark energy. This peculiar feature of heavy-quark jets leads to a specific shape of the fragmentation functions observed in e + e − annihilation. Differently from light flavors, the heavy quark fragmentation function strongly peaks at large fractional momentum z, i.e., the produced heavy–light mesons, B or D, carry the main fraction of the jet momentum. This is a clear evidence of the dead-cone effect, and of a short production time of a heavy–light mesons. Contrary to propagation of a small q q ¯ dipole, which survives in the medium due to color transparency, a heavy–light Q q ¯ dipole promptly expands to a large size. Such a big dipole has no chance to remain intact in a dense medium produced in relativistic heavy ion collisions. On the other hand, a breakup of such a dipole does not affect much the production rate of Q q ¯ mesons, differently from the case of light q q ¯ meson production. [ABSTRACT FROM AUTHOR]

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field ( σ ¯ 3 = f K ± − f K 0 ) and the third generator of the matrix of the explicit symmetry breaking [ h 3 = m a 0 2 f K ± − f K 0 ] are estimated in terms of the decay constants of the neutral ( f K 0 ) and charged Kaon ( f K ± ) and the mass of a 0 meson. Both quantities σ ¯ 3 and h 3 are then evaluated, at finite baryon ( μ B ), isospin chemical potential ( μ I ), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ( T − μ I ) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field ( σ ¯ 3 = f K ± − f K 0 ) and the third generator of the matrix of the explicit symmetry breaking [ h 3 = m a 0 2 f K ± − f K 0 ] are estimated in terms of the decay constants of the neutral ( f K 0 ) and charged Kaon ( f K ± ) and the mass of a 0 meson. Both quantities σ ¯ 3 and h 3 are then evaluated, at finite baryon ( μ B ), isospin chemical potential ( μ I ), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ( T − μ I ) phase diagram. The in-medium modifications of pseudoscalars ( J p c = 0 − + ), scalars ( J p c = 0 + + ), vectors ( J p c = 1 − − ), and axial-vectors ( J p c = 1 + + ) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram ( T − μ I ) is qualitatively similar to the ( T − μ B ) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states a 0 , σ , η ′ , π , f 0 , κ , η , K, ρ , ω , κ * , ϕ , a 1 , f 1 , K * , and f 1 * . Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase. [ABSTRACT FROM AUTHOR]

As known, the realistic, exponential, fall-off of the rate of production of light mesons in the chromo-electric field of a quark–antiquark string, as a function of the meson mass, can be obtained from the Schwinger-formula Gaussian fall-off within a phenomenological approach which assumes a certain distribution of the string tension. This approach gets a clear meaning in the London limit of the dual superconductor, where the logarithmic increase of the chromo-electric field towards the core of the string leads precisely to the change of the Gaussian fall-off to the exponential one, thus allowing for an identification of the phenomenological distribution of the string tension. In this paper, we demonstrate that, for this distribution of the string tension, the distribution of large-size Yang–Mills instantons, which are interacting with the confining monopole background, becomes O (1 / ρ 3) , where ρ is the size of an instanton. Since such a distribution of large-size instantons is known to yield confinement, we conclude that, in the London limit of the dual-superconductor vacuum, instantons can form a confining medium, and we evaluate their contribution to the total string tension. [ABSTRACT FROM AUTHOR]

In this work, we interpret the newly observed η 1 (1855) resonance with exotic J P C = 1 − + quantum numbers in the I = 0 sector, reported by the BESIII Collaboration, as a dynamically generated state from the interaction between the lightest pseudoscalar mesons and axial-vector mesons. The interaction is derived from the lowest order chiral Lagrangian from which the Weinberg–Tomozawa term is obtained, describing the transition amplitudes among the relevant channels, which are then unitarized using the Bethe–Salpeter equation, according to the chiral unitary approach. We evaluate the η 1 (1855) decays into the η η ′ and K K ¯ * π channels and find that the latter has a larger branching fraction. We also investigate its SU(3) partners, and according to our findings, the π 1 (1400) and π 1 (1600) structures may correspond to dynamically generated states, with the former one coupled mostly to the b 1 π component and the latter one coupled to the K 1 (1270) K ¯ channel. In particular, our result for the ratio Γ (π 1 (1600) → f 1 (1285) π) / Γ (π 1 (1600) → η ′ π) is consistent with the measured value, which supports our interpretation for the higher π 1 state. We also report two poles with a mass about 1.7 GeV in the I = 1 / 2 sector, which may be responsible for the K * (1680) . We suggest searching for two additional η 1 exotic mesons with masses around 1.4 and 1.7 GeV. In particular, the predicted η 1 (1700) is expected to have a width around 0.1 GeV and can decay easily into K K ¯ π π . [ABSTRACT FROM AUTHOR]

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can be falling off either as a Gaussian, as suggested by the Schwinger formula, or as an exponential, which is the case in the London limit of the dual superconductor. We find an excellent agreement of the so-evaluated temperature dependence of the string-breaking distance with the respective lattice data, for the case of the meson-production rate corresponding to the London limit. [ABSTRACT FROM AUTHOR]