Narrow Results

The recently obtained solutions of Dirac equation in the confining SU(3)-Yang–Mills field in Minkowski spacetime are applied to describe the energy spectra of quarkonia (charmonium and bottomonium). The nonrelativistic limit is considered for the relativistic effects to be estimated in a self-consistent way and it is shown that the given effects are extremely important for both the energy spectra and the confinement mechanism.

Motivated by recent lattice gauge results that the quarkonium does not dissolve at the critical temperature, we report on recent developments in understanding the properties of charmonium states in the quark gluon plasma using perturbative QCD and QCD sum rule approaches. Using lattice results on the energy density and pressure of pure gauge theory as inputs to the operator product expansion in these theories, we find non trivial property changes of heavy quarkonium across the phase transition.

Heavy quarkonium states are considered as one of the key observables for the study of the phase transition from a system made of hadrons towards a Quark–Gluon Plasma (QGP). In the last 25 years, experiments at CERN and Brookhaven have studied collisions of heavy ions looking for a suppression of charmonia/bottomonia, considered as a signature of the phase transition. After an introduction to the main concepts behind these studies and a short review of the SPS and RHIC results, I will describe the results obtained in Pb–Pb collisions by the ALICE experiment at the LHC. The ALICE findings will be critically compared to those of lower energy experiments, to CMS results, and to model calculations. The large cross-sections for heavy-quark production at LHC energies are expected to induce a novel production mechanism for charmonia in heavy-ion collisions, related to a recombination of pairs along the history of the collision and/or at hadronization. The occurrence of such a process at the LHC will be discussed. Finally, prospects for future measurements will be shortly addressed.

In this article we present a short review on measurements of charmonia production at the LHCb experiment carried out during 2010, 2011 and 2012 data taking periods. The review covers the production of J/ψ, ψ(2S), χ_c, J/ψJ/ψ, as well as J/ψ in association with open charm. We also review the measurement of J/ψ polarization. The results are compared to theoretical predictions.

Recent BESIII data indicate a significant rate of the process e⁺e^- →h_c π⁺ π^- at the Y(4260) and Y(4360) resonances, implying a substantial breaking of the heavy quark spin symmetry. We consider these resonances within the picture of hadrocharmonium, i.e. of (relatively) compact charmonium embedded in a light-quark mesonic excitation. We suggest that the resonances Y(4260) and Y(4360) are a mixture, with mixing close to maximal, of two states of hadrochamonium, one containing a spin-triplet pair and the other containing a spin-singlet heavy quark pair. We argue that this model is in a reasonable agreement with the available data and produces distinctive and verifiable predictions for the energy dependence of the production rate in e⁺e^- annihilation of the final states J/ψππ, ψ′ππ and h_c ππ, including the pattern of interference between the two resonances.

Contrary to almost standard opinion that the $X(3872$) resonance is the $D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ molecule or the $qc\bar{q}\bar{c}$ four-quark state, we discuss the scenario where the $X(3872)$ resonance is the $c\bar{c}={\chi }_{c1}(2P)$ charmonium which “sits on” the $D^{\ast 0}{\bar{D}}^0$ threshold.

We explain the shift of the mass of the $X(3872)$ resonance with respect to the prediction of a potential model for the mass of the ${\chi }_{c1}(2P)$ charmonium by the contribution of the virtual $D^{\ast }\bar{D}+\mathrm{\text{c.c.}}$ intermediate states into the self energy of the $X(3872)$ resonance. This allows us to estimate the coupling constant of the $X(7872)$ resonance with the $D^{\ast 0}{\bar{D}}^0$ channel, the branching ratio of the $X(3872)\to D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ decay, and the branching ratio of the $X(3872)$ decay into all non-$D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ states. We predict a significant number of unknown decays of $X(3872)$ via two gluon: $X(3872)\to \text{gluon gluon}\to \text{hadrons}$.

We suggest a physically clear program of experimental researches for verification of our assumption.

The cross-sections of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ and $e^{+}{e}^{-}\to {\pi }^{+}{D}^0{D}^{\ast -}+\mathrm{\text{c.c.}}$ have been measured by BESIII experiment. A new resonance $Y(4390)$ is observed in the two decay modes. A combined fit is performed to the two cross-sections. $Y(4390)$’s parameters are determined to be $M_{Y(4390)}=(4392.6\pm 4.2\pm 1.0)\mathrm{\text{MeV}}/c^2$, ${\mathrm{\Gamma }}_{Y(4390)}=(154.2\pm 9.3\pm 2.4)\mathrm{\text{MeV}}$, where the first uncertainties are statistical and the second systematic. The ratio $\frac{{ℬ}(Y(4390)\to {\pi }^{+}{D}^0{D}^{\ast -}+\mathrm{\text{c.c.}})}{{ℬ}(Y(4390)\to {\pi }^{+}{\pi }^{-}{h}_c)}$ is also obtained and it indicates that $Y(4390)$’s main decay modes maybe $\pi D{D}^{\ast }$. We determine the lower limit of its leptonic decay width of around 150 eV, which can be compared with the theoretical expectations of different models. These information may help in understanding the nature of this state.

The cross-section of $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ has been measured by BESIII experiment, two enhancements are seen around 4.2 GeV and 4.5 GeV. We try to fit the cross-section with coherent sum of two Breit–Wigner functions, the fit results show $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ line shape can be described by $Y(4220)$ and a new structure around 4.5 GeV, also can be described by the known charmonium $\psi (4160)$ and $\psi (4415)$. Based on current data, we cannot distinguish which explanation is right. More measurements around 4.2 GeV and 4.5 GeV are desired to improve the understanding of the structures in $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$.

We discuss the power scaling rules along the lines of a complete heavy quark effective field theory (HQEFT) for the description of heavy quarkonium production through a color-octet mechanism. To this end, we firstly derive a tree-level heavy quark effective Lagrangian keeping both particle–antiparticle mixed sectors allowing for heavy quark–antiquark pair annihilation and creation, but describing only low-energy modes around the heavy quark mass. Then we show the consistency of using HQEFT fields in constructing four-fermion local operators à la NRQCD, to be identified with standard color-octet matrix elements. We analyze some numerical values extracted from charmonia production by different authors and their hierarchy in the light of HQEFT.

The variational method and the Hamiltonian formalism of QCD are used to derive relativistic, momentum space integral equations for a quark–antiquark system with an arbitrary number of gluons present. As a first step, the resulting infinite chain of coupled equations is solved in the nonrelativistic limit by an approximate decoupling method. Comparison with experiment allows us to fix the quark mass and coupling constant, allowing for the calculation of the spectra of massive systems such as charmonium and bottomonium. Studying the results with and without the non-Abelian terms, we find that the presence of the non-Abelian factors yields better agreement with the experimental spectra.

We study the quantum-mechanical evolution of the nonrelativistic oscillator, rapidly moving in the media with the random vector fields. We calculate the evolution of the level probability distribution as a function of time, and obtain rapid level diffusion over the energy levels. Our results imply a new mechanism of charmonium dissociation in QCD media.

We report recent results on the properties of the X(3872) produced via the B⁺→K⁺ X(3872) decay process in the Belle detector. We compare these properties with expectations for possible charmonium-state assignments.

Recent results on charmonia decays at BESII/BEPC are reported, including the observation of , ψ′→Vector Tensor and ψ′→Vector Pseudoscalar for the measurement of the relative phase between the strong and electromagnetic decays of ψ′ and a test of the pQCD "12% rule" between ψ′ and J/ψ decays; the test of the color-octet mechanism via and ; the first observation of χ_c0→f₀(980)f₀(980); and a study of the ψ′ and χ_cJ decays with in the final states.

Results are reported based on samples of 58 million J/ψ and 14 million ψ(2S) decays obtained by the BESII experiment. Improved branching fraction measurements are determined, including branching fractions for J/ψ→π⁺π^-π⁰, ψ(2S)→π⁰J/ψ, ηJ/ψ, π⁰π⁰J/ψ, anything J/ψ, and ψ(2S)→γχ_c1, γχ_c2→γγJ/ψ. The decay J/ψ→ωπ⁺π^- is studied. At low ππ mass, a large, broad peak due to the σ is observed, and its pole position is determined. Results are presented on ψ(2S) and J/ψ hadronic decays to and final states. No significant Θ(1540) signal, the pentaquark candidate, is observed, and upper limits are set. An enhancement near the m_p+M_Λ mass threshold is observed in the invariant mass spectrum from decays. It can be fit with an S-wave Breit-Wigner resonance with a mass m=2075±12 (stat)±5 (syst) MeV and a width of Γ=90±35 (stat)±9 (syst) MeV.

A major component of the approved upgrade of the GSI facility in Darmstadt, Germany is the High Energy Storage Ring (HESR) for high intensity, phase space cooled antiprotons with momenta up to 15 GeV/c. At this facility a wide physics program is planned to investigate both the structure of hadrons in the charmonium mass range and the spectroscopy of double hypernuclei. To serve the many experiments planned at this new facility, a general purpose detector called PANDA (Proton ANtiproton Detector Array) is planned. An overview of the PANDA detector concept, as well as selected results from simulation of the detector's performance will be presented.

Recently GSI presented the plans for a major new international research facility, called FAIR. A key feature of this new facility will be the delivery of intense, high-quality secondary beams which embody the production of antiprotons. For the antiproton beams a High Energy Storage Ring (HESR) is comprised. The design luminosity is 2·10³²cm^-2s^-1. Experiments will take place at an internal target. The rich spectroscopy program on exotic hadrons with antiproton beams is presented.

This paper gives an introduction to the hadron physics program and the planned PANDA experiment at the future FAIR facility located at GSI in Germany.

Recent results on charmonia decays at BES II are reported, including the measurements of ψ(2S) → Vector-Pseudoscalar, ψ(2S) → Vector-Tensor and for a test of the pQCD "12% rule" between ψ(2S) and J/ψ decays; the first observations of χ_c0 → f₀(980)f₀(980), ; and a study of the pentaquark state in ψ(2S) and J/ψ decays.

Last year's X(3872) discovery was confirmed with the CDF II detector in collisions. We measure its mass to be 3871.3±0.7±0.4 MeV/c². The source of X-mesons in the large CDF sample is resolved by studying their vertex displacement. We find 16.1±4.9±2.0% of our X-sample comes from decays of b-hadrons, and the remainder from prompt sources: either direct production or by decay of (unknown) short-lived particles. The mix of production sources is similar to that observed for the ψ(2S) charmonium state.

We report measurements of B decay modes involving the newly discovered D_sJ and X(3872) particles. Possible spin-parity and quark content assignments of these new states are discussed. The results are based on a large data sample recorded by the Belle detector at the KEKB e⁺e^- collider.