Quarkonium Interactions in QCD
Contents: 1. Introduction 2. Operator Product Expansion for Quarkonium Interactions 3. Scale Anomaly, Chiral Symmetry and Low-Energy Theorems 4. Quarkonium Interactions in Matter 5. Conclusions and Outlook
nucl-th↗
arXiv subjects
D. Kharzeev
Publications and source records attributed to D. Kharzeev.
J/Psi Suppression in an Equilibrating Parton Plasma
Short-distance QCD is employed to calculate the $J/ψ$ survival probability in an equilibrating parton gas, whose evolution is governed by a set of master rate equations. Partons in the early stage of high-energy nuclear collisions may initially not be in equilibrium, but their average transverse momentum is sufficiently high to break up a $Q\bar{Q}$ bound state. Such a break-up during the evolution of the parton gas is shown to cause a substantial $J/ψ$ suppression at both RHIC and LHC energies, using realistic estimates of the initial parton densities. The transverse momentum dependence of the suppression is also shown to be sensitive to the initial conditions and the evolution history of the parton plasma.
hep-ph↗
CP-Violating Effect of QCD Vacuum in Quark Fragmentation
We demonstrate that the non-trivial CP-violating structure of QCD vacuum can lead to an observable effect in $e^+e^-\to q\bar q\to 2$-jet annihilation. We find that the sign of the jet handedness correlation can be opposite to that predicted by factorization of $q~\bar q$ fragmentation and CP-conjugation of the two jets. A simple model estimation of the handedness correlation magnitude is given.
hep-ph↗
The Return of The Prodigal Goldstone Boson
We propose that the mass of the $η^\prime$ meson is a particularly sensitive probe of the properties of finite energy density hadronic matter and quark gluon plasma. We argue that the mass of the $η^\prime$ excitation in hot and dense matter should be small, and therefore that the $η^\prime$ production cross section should be much increased relative to that for pp collisions. This may have observable consequences in dilepton and diphoton experiments.
hep-ph↗
Charmonium Composition and Nuclear Suppression
We study charmonium production in hadron-nucleus collisions through the intermediate next-to-leading Fock space component $|(\bar{c}c)_8 g>$, formed by a colour octet $\bar{c}c$ pair and a gluon. We estimate the size of this state and show that its interaction with nucleons accounts for the observed charmonium suppression in nuclear interactions.
hep-ph↗
Colour Deconfinement and Quarkonium Dissociation
We survey how quarkonia can be used to probe colour deconfinement in relativistic nuclear collisions.
hep-ph↗
Charmonium Interactions in Nuclear Matter
We analyse the kinematic regimes attainable for $J/Ψ$ and $Ψ'$ production in $p-A$ collisions. With this information, we specify the requirements for an experiment to study the interaction of physical charmonium states in nuclear matter, making use of a heavy ion beam incident on a hydrogen or deuterium target.
hep-ph↗
Non-perturbative Quarkonium Dissociation in Hadronic Matter
We calculate the dissociation rates of quarkonium ground states by tunnelling and direct thermal activation to the continuum. For hadronic matter at temperatures $T \leq 0.2$ GeV, neither of these mechanisms leads to a sufficiently large dissociation to explain the experimentally observed suppression of charmonium. Dissociation by sequential excitation to excited energy levels, although OZI-forbidden, requires further analysis.
hep-ph↗
THE PROTON SPIN PUZZLE AND DEPOLARIZATION IN $\bar{p}p\to\barΛΛ$
We point out that the measurement of target spin depolarization $D_{nn}$ in the $\bar{p}p\to\barΛΛ$ reaction may test dynamical mechanisms invoked to explain the proton spin puzzle revealed by polarized deep--inelastic scattering experiments. In particular, models with {\it negatively} polarized $\bar{s}s$ pairs in the proton wave function predict $D_{nn}<0$, whereas models with {\it positively} polarized gluons would predict $D_{nn}>0$.
hep-ph↗
Quarkonium production in hadronic collisions
We summarize the theoretical description of charmonium and bottonium production in hadronic collisions and compare it to the available data from hadron-nucleon interactions. With the parameters of the theory established by these data, we obtain predictions for quarkonium production at RHIC and LHC energies.
hep-ph↗
Nucleon-Antinucleon Annihilation at the Open Charm Threshold
We discuss the $p\bar{p}$ annihilation into a pair of charmed $D$ mesons not far from the threshold of the reaction. An interesting interference pattern in the differential cross section is predicted to arise from the existence of both $t$-channel charmed-baryon exchange and $s$-channel $Ψ^{''}$ charmonium resonance amplitudes. We argue that the experimental study of this process would provide new and valuable information about the unknown $p\bar{p}Ψ^{''}$ and $Λ_c N D$ couplings. These are important to know to solve the long-standing puzzle of the heavy flavour contents of baryons and to test the semi-local duality.
hep-ph↗
Chiral Dynamics, Deconfinement and Thermal Dileptons
We show that in a hot hadron gas, chiral symmetry restoration and deconfinement lead to a strong suppression of dilepton production by pion annihilation in the continuum above the $ρ-ω-ϕ$ peak. The suppression due to deconfinement persists also for annihilation reactions involving heavier mesons.
hep-ph↗
Quarkonium Interactions in Hadronic Matter
The cross section for the \J~and \U~interaction with light hadrons is calculated in short-distance QCD, based on the large heavy quark mass and the resulting large energy gap to open charm or beauty. The low energy form of the cross section is determined by the gluon structure functions at large $ x$; hence it remains very small until quite high energies. This behaviour is experimentally confirmed by charm photoproduction data. It is shown to exclude \J~absorption in confined hadronic matter of the size or density attainable in nuclear collisions; in contrast, the harder gluon spectrum in deconfined matter allows break-up interactions.
hep-ph↗