The processes of D^{(*)}-mesons and Λ_c-baryons production in e^+e^--annihilation at 10.58 GeV and 91.18 GeV energies are concerned. At the 10.58 GeV energy the production of charmed particles via the B-mesons decays is also concerned. Scaling violation of the fragmentation functions is calculated at the NLL-accuracy. Nonperturbative fragmentation functions are retrieved from the experimental data of B-factories and are approximated by simple analytic expressions. It is proved, that the difference between nonperturbative fragmentation functions of mesons and baryons can be easily explained by quark counting.
The cross section value of doubly charmonium production in e+e- annihilations have been estimated at interaction energy 10.6 GeV. The quarkonium wave function shape, as well as the nonzero value of charm quark have been taken into account.
In the framework of quark-hadron duality, the cross section values of charmonium and doubly charmed baryon production in $e^+e^-$-annihilations have been estimated at interaction energy $\sqrt{s}=10.6$ GeV. It has been shown that the approach under discussion allows to resolve some contradictions between the experimental data and pQCD predictions.
The total and differential cross sections for the production of triply charmed $Ω_{ccc}$ baryons in $e^{+}e^{-}$ annihilation are calculated at the $Z$-boson pole.
In this paper initial state radiation corrections to double production of charmonium mesons on one-photon electron-positron annihilation at center of mass energy $\sqrt{s}=10.6\GeV$ are studied. It is shown, that these corrections have noticeable effect and must be taken into consideration.
We discuss the hadroproduction of charmed mesons in the framework of the constituent cascade model taking into account the valence quark annihilation. It is shown that the small valence quark annihilation process dominates the leading particle production at large Feynman x and explains the recent experimental data on the asymmetry between D^0 and D^0 bar at 350 GeV/c.
In the pole-dominance model for the two-body nonleptonic decays of charmed mesons $D \rightarrow PV$ and $D \rightarrow VV$, it is shown that the contributions of the intermediate pseudoscalar and the axial-vector meson poles cancel each other in the annihilation diagrams in the chiral limit. In the same limit, the annihilation diagrams for the $D \rightarrow PP$ decays vanish independently.
Recent measurements of the Belle Collaboration of the exclusive production of two charmonia in the $e^+e^-$ annihilation differ substantially from theoretical predictions. Recently it was suggested that a significant part of this discrepancy can be explained by the process $e^2e^- --> 2J/psi$ and value for its cross-section was published. In this paper it is shown, that these results are incorrect and the values for the cross-sections of the production of different vector charmonia are presented.
We review the charmonium production in $e^+e^-$ annihilation at $\sqrt{s}=10.6GeV$. NRQCD predictions for the $J/ψ$ production are compared with the recent measurements by BaBar and Belle. A NRQCD calculation for the $D$-wave charmonium production is reported to further test the color-octet mechanism and detect the $J^{PC}=2^{--}$ state. The issue of double $c \bar c$ production in $e^+e^-$ annihilation observed by Belle is also discussed.
In this paper the production of excited vector and pseudoscalar charmonium mesons in $\epem$ annihilation is analyzed in the framework of light cone. In particular the cross sections $\epem \to ψ(2S)η_c(1S), ψ(1S)η_c(2S),ψ(2S)η_c(2S)$ have been calculated. It is shown, that contrary to NRQCD the cross sections calculated in the framework of light cone agree with experimental data.
It is suggested that the recently observed enhancement of the relative yield in $e^+e^-$ annihilation of states with hidden charm and hidden strangeness above 4.43\,GeV is associated with the $S$ wave production of the charmed strange meson pairs $D_{s0}(2317) \bar D_s^* + {\rm c.c.}$ and $D_{s1}^*(2460) \bar D_s+ {\rm c.c.}$. This mechanism implies a pattern of breaking of the Heavy Quark Spin Symmetry (HQSS) that can be tested in the final channels such as $η_c(1S) ϕ$, $h_c(1P) η$, $h_c(1P) η' $ produced in the same energy range.
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…
In this paper we study inclusive production of vector charmonium states $J/ψ$ or $ψ(2S)$ in two-photon $\epem$-annihilation at $\sqrt s=10.6 \rm GeV$ using color-singlet model. Analytic expressions for differential cross sections, numerical values of total cross sections and plots of different distributions are presented. These distributions differ significantly from the one-photon case so these modes can be easily separated.
We calculate the double charmonium production cross section within the framework of $4\times 4$ Bethe-Salpeter Equation in the electron-positron annihilation, at center of mass energy $\sqrt{s}= 10.6$GeV, that proceeds through the exchange of a single virtual photon. In this calculation, we make use of the full Dirac structure of 4D BS wave functions of these charmonia, with the incorporation of all the Dirac covariants (both leading and sub-leading). The calculated cross-sections for the double charmonium productions for final states, ($J/Ψ, η_c$); ($Ψ',η_c$) ; ($J/Ψ, η_c'$); and ($Ψ',η_c'$) …
The production cross sections of $J/ψ~η_b$, $Υ\;η_c$ pairs in a single boson $e^+e^-$ annihilation have been studied in a wide range of energies, which will be achieved at future $e^+e^-$ colliders. The main color singlet contributions to the production processes are taken into account, including the one loop QCD contribution.
We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as $\ldc\to\ldπ^+,Σ^0π^+,p \bar K_0$, $Ξ_c^0\toΞ^-π^+$ and $Ω_c^0\toΩ^-π^+$. The joint angular formulae for these processes are presented, and are used to extract the asymmetry parameters in $\ee$ annihilation data. Base on the current $\ldc$ data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters $α_{\ldπ^+}$ for $\ldc\to\ldπ^+$, $α_{Σ^+π^0}$ for $\ldc\toΣ^+π^0$ and $α_{\usigπ^+}$ for $\ldc\to\usigπ^+$.
We suggest searching for excited charmonium states in $e^+e^-$ annihilation via double charmonium production at $\sqrt{s}=10.6$ GeV with $B$ factories, based on a more complete leading order calculation including both QCD and QED contributions for various processes. In particular, for the C=+ states, the $χ_{c0}(nP)$ (n=2,3) and $η_c(mS)$ (m=3,4) may have appreciable potentials to be observed; while for the C=- states, the $η_ch_c$ production and especially the $χ_{c1}h_c$ production might provide opportunities for observing the $h_c$ with higher statistics in the future. A brief discussion fo…
We calculate the contributions from QED processes involving two virtual photons to the cross sections for e^+ e^- annihilation into two charmonium states with the same C-parity. Generically, the cross sections are three orders of magnitude smaller than those for charmonia with opposite C-parity because they are suppressed by a factor of alpha^2/alpha_s^2. However, if both charmonia have quantum numbers J^{PC} = 1^{--}, then there is a contribution to the cross section that involves the fragmentation of each photon into a charmonium. The fragmentation contribution is enhanced by powers of E_{be…
We calculate the D-wave charmonium production in $e^+e^-$ annihilation at BELLE and BABAR at $\sqrt{s}=10.6$ GeV using the nonrelativistic QCD factorization formalism, including color singlet and color octet contributions. We analyze the contributions of various processes for $δ_J(J=1,2)$ production. We find that both the color singlet and color octet channels may give substantial contributions, and the production rates are estimated to be $σ(δ_1)\simeq 0.043-0.16pb$ and $σ(δ_2)\simeq 0.094-0.29pb$, which, however, are very sensitive to the choice of the color octet matrix elements of the D-wa…
We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on pbarp to KbarK by connecting the processes via SU(4) flavor symmetry. Our predictions for the DDbar production cross section are in the order of 10^{-2} -- 10^{-1} mu b. They turned out to be …
The associated production of a $J/ψ$ and a $π$-meson in antiproton-nucleon annihilation is studied in the framework of QCD collinear factorization. In this approach, a hard subprocess responsible for the production of the heavy quark-antiquark pair factorizes from soft hadronic matrix elements, such as the antiproton (nucleon) distribution amplitude and the nucleon-to-pion (antiproton-to-pion) transition distribution amplitude. This reaction mechanism should dominate the forward and backward kinematical regions, where the cross sections are expected to be measurable in the set-up of the PANDA …
Inspired by the observation of charmoniumlike $Z(4200)$, we explore the discovery potential of the neutral $Z^{0}(4200)$ production by antiproton-proton annihilation with an effective Lagrangian approach. By investigating the $\bar{p}p\rightarrow J/ψπ^{0}$ process including the $Z^{0}(4200)$ signal and background contributions, it is found that the center of mass energy $E_{c.m.}\simeq 4.0-4.5$ GeV is the best energy window for searching the neutral $Z^{0}(4200)$, where the signal can be clearly distinguished from background. The relevant calculations is not only helpful to search for the neut…
We calculate the exclusive cross sections for e^+ e^- annihilation into two charmonium states through a virtual photon. Purely electromagnetic contributions are surprisingly large, changing the cross sections by as much as 21%. The predicted cross section for J/psi + eta_c is about an order of magnitude smaller than a recent measurement by the BELLE Collaboration, although part of the discrepancy can be attributed to large relativistic corrections. The cross sections for S-wave + P-wave, P-wave + P-wave, and S-wave + D-wave charmonium states are also calculated. It may be possible to discover …
Measurements by the Belle Collaboration of the exclusive production of two charmonia in e^+ e^- annihilation differ substantially from theoretical predictions. Till now, no conclusive explanation for this remarkable discrepancy has been provided. Even the origin of the discrepancy is not identified, yet. We suggest that the measurement of four-charm events in Belle data must provide a strong constraint in identifying the origin of this large discrepancy. Our prediction of the cross section for e^+e^- -> c c-bar c c-bar, in lowest order in strong coupling constant, at sqrt{s}=10.6 GeV is about …
We present the gluon-gluon and photon-gluon helicity amplitudes for color singlet and octet charmonium production in polarized and unpolarized hadron-hadron and photon-hadron collisions.
In this work we study the process $e^{+}+e^{-}\longrightarrow J/Ψ+η_{c} $ at energy $\sqrt{s}= 10.6 GeV$ observed recently at B-factories whose measurements were made by Babar and Belle groups. We calculate the cross section for this process in the Bethe-salpeter formalism under Covariant Instantaneous Anstaz (CIA). To simplify our calculation, the heavy quark approximation $(q<<M, P M)$ is employed in the quark and gluon propagators. In the exclusive process of $e^{+}e^{-}$ annihilation into two heavy quarkonia, the cross section calculated in this scenario is compatible with the experimental…
Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\bar{p}p\rightarrow J/ψJ/ψ$ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, rel…
In this paper we summarize our recent results for low energy associated charmonium production cross sections, using 1) crossing symmetry, and 2) an explicit hadronic model. These predictions are of relevance to the planned charmonium and charmonium hybrid production experiment PANDA at GSI.
In this talk, we show our recent theoretical results for three-body systems in the charm sector which are made of three hadrons and contain one nucleon, one $D$ meson and in addition another meson, $\bar{D}$, $K$ or $\bar{K}$.
We calculate the cross section for $e^+ e^-$ annihilation into $D^{*0} \bar D^0 +γ$ at center-of-mass energies near the $D^{*0} \bar D^{*0}$ threshold under the assumption that $X(3872)$ is a weakly bound charm meson molecule. The Dalitz plot has a $\bar D^{*0}$ resonance band in the squared invariant mass $t$ of $\bar D^0 γ$. In the limit as the decay width of the $D^{*0}$ goes to 0, the Dalitz plot also has a narrow band in the squared invariant mass $u$ of $D^{*0} \bar D^0$ from a charm-meson triangle singularity. At the physical value of the $D^{*0}$ width, the narrow band reduces to a sho…
New evaluation of the relativistic effects in the double production of $S$-wave charmonium states is performed on the basis of perturbative QCD and the relativistic quark model. The main improvement consists in the exact account of properties of the relativistic meson wave functions. For the gluon and quark propagators entering the production vertex function we use a truncated expansion in the ratio of the relative quark momenta to the center-of-mass energy $\sqrt{s}$ up to the second order. The exact relativistic treatment of the wave functions makes all such second order terms convergent, th…
I discuss the special opportunities that a Tau-Charm Factory offers for identifying gluonic excitations, hybrid charmonium and other exotic hadronic states. (Invited talk at TCF Workshop, Marbella, 1-6June)
We discuss the decay of Bc mesons into two light mesons (pi, K^(*), eta', rho, omega, phi). All these decay channels come from a single type of diagram, namely tree annihilation. This allows us to derive extremely simple SU(3) relations among these processes. The size of annihilation contributions is an important issue in B physics, and we provide two different estimates in the case of non-leptonic charmless Bc decays, either a comparison with annihilation decays of heavy-light mesons or a perturbative model inspired by QCD factorisation. We finally discuss a possible search for these channels…
In the hadroproduction of charm in the context of string fragmentation, the pull of a beam remnant at the other end of a string may give a charm hadron more energy than the perturbatively produced charm quark. The collapse of a low-mass string to a single hadron is the extreme case in this direction, and gives rise to asymmetries between charm and anticharm hadron spectra. We study these phenomena, and develop models that describe the characteristics not only of the charm hadrons but also of the associated event.
It is shown that the D--meson, whose light quark is the initial-pion valence quark and whose charmed quark is produced in annihilation of valence quarks and has got a large enough momentum, is really a leading meson in reactions like $π^- p -> DX$. If such annihilation of valence quarks from initial hadrons is impossible there must be no distinct leading effect.
We study the production of charmed mesons (D) and baryons (Lambda_c) in antiproton-proton (app) annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on app -> antiLambda-Lambda and app -> antiK-K by connecting the processes via SU(4) flavor symmetry. Our predictions for the antiLambda_c-Lambda_c production cross …
We calculate the form factor and cross section of the excited charmonium production process $e^{+}+e^{-}\rightarrow ψ\left ( 2S \right )+η_{c}$ by light-cone sum rules. In our method, the form factor depends on the distribution amplitude of $η_{c}$ meson. Experimentally, the energy scale of $e^{+}+e^{-}\rightarrow ψ\left ( 2S \right )+η_{c}$ process is much larger than the initial energy scale of $η_{c}$ meson in our BHL model. Therefore, we further consider the evolution of the distribution amplitude with the energy scale, and select the distribution amplitude as our input parameter when the …
We present the calculation of the inclusive x_F-distributions of charmed hadrons, produced in high-energy $Σ^-$-beam. Our calculation is based on the modified mechanism of charmed quarks fragmentation as well as on the mechanism of c-quark recombination with the valence quarks from initial hadrons.
A resently developed generalization of the Quark--Gluon String Model to the case of bosonic resonances production in hadron--hadron collisions is used for the calculation of inclusive production of charmed mesons $D$, $D^*(2010)$ and $D^{*}_{2}(2460)$. A simple relation which determines the dependence of the charmed meson production cross sections on their spin J is obtained. It is shown that the theoretical predictions for the inclusive spectra and production cross sections of these charmed mesons are confirmed experimentally with a reasonable accuracy.
We study $Λ_c^\pm$ production in $pN$ and $π^-N$ interactions. Recent experimental data from the SELEX and E791 Collaborations at FNAL provide important information on the production mechanism of charm hadrons. In particular, the production of the $Λ_c$ baryon provides a good test of the intrinsic charm and the recombination mechanisms, which have been proposed to explain the so called leading particle effects.
We study charm particle production in hadron-hadron collisions. After calculating perturbatively the charm quark differential cross section, we study the hadronization mechanisms. It is shown that recombination is the key to understand the so called Leading Particle Effect in charm meson production. For charm baryon production, however, leading particle effects are due to a combination of contributions coming from both, the recombination and the fragmentation mechanisms. We compare our calculations to experimental data on charm hadron production in $π^- N$ and $p N$ interactions from several e…
Recently the ALICE Collaboration has published a few data of charm hadrons in Pb + Pb collisions at the CERN Large Hadron Collider (LHC). We extend the quark combination to the charm sector and point out that the measurement of charm hadron yields can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios, e.g. $D^{*+}/D^0$, $D_s^+/D^+$ and $Λ_c^+/D_s^+$, to measure various properties of low $p_T$ charm quark hadronization. We argue that ratios $D_s^+/D^0$ and $2D…
We analyze the charm quark electric dipole moment (EDM) in the minimal supersymmetric extension of the standard model (MSSM), including important two-loop gluino contributions. Considering the experimental constraint on the neutron EDM, the theoretical prediction for the charm quark EDM can reach about $10^{-20}e\cdot cm$. If taking into account the mixing between the scharm and stop quarks in the effective supersymmetry scenario, the charm quark EDM can be enhanced to $\sim 10^{-19}e\cdot cm$. Direct production of the CP-odd $^1P_1$ state $h_c$ in $e^+e^-$ annihilation via the CP-violating pr…
In calculations of the hyperfine splitting in charmonium, the contributions of the disconnected diagrams are considered small and are typically ignored. We aim to estimate nonperturbatively the size of the resulting correction, which may eventually be needed in high precision calculations of the charmonium spectrum. We study this problem in the quenched and unquenched QCD cases. On dynamical ensembles the disconnected charmonium propagators contain light modes which complicate the extraction of the signal at large distances. In the fully quenched case, where there are no such light modes, the …
Leading charm hadrons produced in hadron-nucleus interactions cannot be adequately described within the parton fusion model. Recent results on charm baryon production in $Σ^- A$ interactions at 330 GeV with the WA89 detector disagree with fusion predictions. Intrinsic heavy quark pairs in the $Σ^-(dds)$ wavefunction provide a simple mechanism for producing fast charm hadrons. We calculate leading charm baryon production from $Σ^-$, $π^-$ and $p$ projectiles in a two component model combining parton fusion with intrinsic charm. Final state $D^{-}$, $Σ_{c}^{0}$, $Ξ_{c}^{+}$, and $Λ_{c}^{+}$ $dσ/…
The cross sections for the charmonium production processes p pbar -> m Psi, where m is a light meson and Psi is a charmonium state, are of great interest for the planned p-pbar experiment PANDA. In this paper we estimate these cross sections using known results for the decays Psi -> m p pbar which are related to these reactions by crossing. In lieu of detailed experimental data on the decay Dalitz plots, we assume a constant amplitude as a first approximation; this implies a simple relation between the cross sections and decay widths. The single measured exclusive cross section of this type is…
We discuss the relative role of fragmentation and recombination processes for heavy flavour hadron production in different kinematical regions in high energy hadron-hadron and photon-hadron collisions. We predict several qualitative features which should be observed if our picture of heavy flavour production is consistent.
Fermilab experiment E791, measuring charmed hadron production in $π^- A$ interactions at 500 GeV with high statistics, has observed a strong asymmetry between the hadroproduction cross sections for leading $D$ mesons which contain projectile valence quarks and the nonleading charmed mesons without projectile valence quarks. Such correlations of the charge of the $D$ meson with the quantum numbers of the beam hadron explicitly contradict the factorization theorem in perturbative QCD which predicts that heavy quarks hadronize through a jet fragmentation function that is independent of the initia…
We give the first estimate of charmless scalar meson emitting weak hadronic decays of 0 $\Lembda_{b}^{0}$, $Ξ_{b}^{0}$ and $Ξ_{b}^{-}$ bottom baryons employing the pole model and consequently predict their branching ratios.
On the basis of perturbative QCD and the relativistic quark model we calculate relativistic and bound state corrections in the production processes of a pair of P-wave charmonium states. Relativistic factors in the production amplitude connected with the relative motion of heavy quarks and the transformation law of the bound state wave function to the reference frame of the moving P-wave mesons are taken into account. For the gluon and quark propagators entering the production vertex function we use a truncated expansion in the ratio of the relative quark momenta to the center-of-mass energy s…
Hybrid charmonium with mass ~4 GeV could be produced via a c c.bar color-octet component in b->c c.bar s. These states could be narrow and could have a significant branching ratio to light hadrons, perhaps enhanced by glueballs. Decays to gluonic hadrons could make a sizable contribution to B->no charm decays. Experimental signatures and search strategies are discussed.
The effects of the intrinsic charm on the hadronic production of $Ξ_{cc}$ are studied. By taking reasonable intrinsic charm component into account, the change of the theoretical prediction on the production of $Ξ_{cc}$ for LHC and Tevatron is small, but in contrast it may enhance significantly for SELEX. The reason is that the collision energy at LHC and Tevatron is so large that the gluon-gluon fusion sub-process, which is irrelevant to intrinsic charm, becomes dominant. But the situation for SELEX is quite different. Our numerical results for SELEX show that by considering all the contributi…
Caution is suggested on the comparison of the spin-singlet charmonium P-state with the centre of gravity of triplet states, when the mass splitting is of the order of a few MeV. The physics of new hidden-charm states X and Y is briefly reviewed. Perspectives for producing double-charm baryons and double-charm exotic mesons are discussed.
The experimental data of BELLE Collaboration on the exclusive charmed meson pair production in the process of monophotonic $e^+e^-$-annihilation ($e^+e^-\to γ^* \to D\bar D$) has been studied. It has been shown that these data is described satisfactorily in the frame work of constituent quark model. Our studies have demonstrated that the central production process $e^+e^-\to e^+e^-γγ\to e^+e^-D\bar D +X$ and the process of monophotonic $e^+e^-$-annihilation yield comparable numbers of the charmed meson pairs.
Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model (SCM). Charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At hadronization, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with laws of statistical mechanics. Important special cases: a system with a small number of charmed quark-antiquark pairs and charm hadronization in a subsystem of t…
Motivated by the recent observation of double charm quark pair production by the Belle Collaboration, we calculate the complete ${\cal O}(α_{s}^{2})$ inclusive production cross sections for $η_{c}$, $J/ψ$, and $χ_{cJ}$(J=0, 1, 2) plus $c\bar{c}$ in $e^+ e^-$ annihilation through a virtual photon. We consider both color-singlet and color-octet contributions, and give the analytical expressions for these cross sections. The complete color-singlet calculations are compared with the approximate fragmentation calculations as functions of the center-of-mass energy $\sqrt{s}$. We find that most of th…
The weak decay of charmed baryons multiplets into ground state and mesons are investigated using current algebra technique. Some of the interesting results on the partial decays rates and the asymmetry parameters for $Δ$C=$Δ$S=-1 the mode are calculated and consequences discussed
The physics of charm has become one of the best laboratories exposing the limitations of the naive constituent quark model and also giving hints into a more mature description of hadron spectroscopy. Recent discoveries are a challenge that have revolutionized our understanding of the hadron spectra. In this talk we address the study of many-quark components in charmonium spectra. To make the physics clear we also discuss exotic many-quark systems.
We propose a modification of the mechanism of charmed quarks fragmentation into $D$ mesons in hadronic collisions. It is shown that the distinction in valence quark distributions in the initial $π^{\pm}$ and $K^{\pm}$ mesons leads to different inclusive spectra of $D$ and $D_s$ mesons produced in $π^{\pm}$ and $K^{\pm}$ beams.
We provide a brief summary of recent developments in QCD calculations in and beyond fixed-order perturbation theory, for observables in $e^{+}e^{-}$ annihilation as well as hadron collisions.
A selected survey is presented of the recent progress in hadron spectroscopy. This includes spin-singlet charmonium states, excitations of charmonium and open-charm mesons, double-charm baryons, and pentaquark candidates. Models proposing exotic bound states or resonances are reviewed. The sector of exotic mesons with two heavy quarks appears as particularly promising.
