Narrow Results

Mixing in the D⁰ system may provide a sensitive probe for new physics beyond the Standard Model (SM) but has so far eluded experimental observation. The SM predictions are typically small (< 10^-3) for the mixing parameters x, y which, in the absence of charge-parity (CP) symmetry violation, measure the mass (x = Δ m/Γ) and lifetime (y = ΔΓ/2Γ) difference of the CP eigenstates in the D⁰ system. The asymmetric B-factory experiments BABAR and Belle open up the opportunity of measuring x, y with unprecedented statistical precision and sample purities. Results from BABAR and Belle, and from CLEO are reviewed.

Motivated by the recent surprising discovery of two new meson states with quark content but unexpectedly low masses and narrow total decay widths, we work out, in a nonrelativistic potential-model approach developed already some two decades ago, the predictions for the energy levels of the corresponding charm–anti-strange quark bound states. In spite of the fact that this simple quark model reproduces the mass spectrum of the previously observed hadrons remarkably well, we are led to the conclusion that, without considerable modifications, both the new states do not fit into this framework.

The BaBar experiment has discovered an unexpected new narrow state, in the inclusive invariant mass distribution from e⁺e^- annihilation data at energies near 10.6 GeV. The same experiment has also shown evidence for structure in the 2.46 GeVc² region in the mass spectrum. These discoveries have triggered a search in several experiments for new states coupled to the meson which have confirmed the existence of together with both in inclusive e⁺e^- annihilation and in B-decays. These two new states are difficult to explain in terms of potential models.

We review the theoretical and experimental evidence for the candidacy of the and the for charmed tetraquarks. We briefly review the 't Hooft interaction's influence on the single-charm (C = 1) tetraquark mass spectrum: its consequences for other observed mesons such as the , as well as its predictions of the (thus far) unobserved exotic tetraquark states. In particular we show that the small mass difference is naturally predicted by the tetraquark model, within the present experimental error bars, and thus may constitute the first "smoking gun" evidence for tetraquark existence. A short outlook of the possible future research directions is given.

The recently discovered scalar and axial vector charmed strange mesons are predicted in the hadrogenesis picture. They are generated by coupled-channel dynamics involving the scattering of Nambu-Goldstone bosons off pseudoscalar and vector D(D_s)-meson ground-states. The interaction vertices are given by the leading order chiral Lagrangian and chiral corrections to order . To assess this dynamical picture further, the radiative and strong decays into the isospin-violating π⁰D_s and channels are calculated. A consistent picture of these decays emerges when the parameters are chosen in accordance with expectations from the heavy-quark symmetry and large N_c limit of QCD and when light vector mesons are introduced explicitly in the radiative decay processes. More accurate data are needed to predict decay parameters reliably.

Detector PANDA was proposed for studies of the interaction of antiprotons with nucleons and nuclei at the future GSI accelerator facility. Selected topics of physics program at PANDA including studies of the interaction of charmed hadrons in matter, production of double Λ-hypernuclei, CP-violation in the and system as well as studies of electromagnetic form factors of proton are presented.

We present a study of and D_sJ(2460)⁺ meson production in B decays based on a data sample of 122 million pairs collected with the BABAR experiment.

We review the theoretical and experimental evidence for the candidacy of the , and the for charmed tetraquarks. We briefly review the 't Hooft interaction's influence on the single-charm (C=1) tetraquark mass spectrum: its consequences for other observed mesons such as the , as well as its predictions of the (thus far) unobserved exotic tetraquark states. In particular we show that the near mass degeneracy of and was naturally predicted by the tetraquark model with 't Hooft interaction, and thus may constitute the first "smoking gun" evidence for tetraquark existence. A short outlook of possible future research directions is given.

Many new results on charm physics were obtained recently. We review of the experimental status in charm and charmonium decay, production and spectroscopy, together with the theoretical interpretations and the open questions.

The Belle experiment at the KEKB asymmetric-energy e⁺e^- collider provides an excellent environment not only for B physics, but also for studies in charm and charmonium spectroscopy. The paper gives a summary of recent Belle achievements in this field.

The positive parity scalar and axial-vector charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(D_s)-meson ground states. The attraction leading to the specific masses of these states reflects the chiral symmetry breaking scale which characterizes the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order are calculated and found to be small. The and mesons decay either strongly into the isospin-violating π⁰D_s and channels or electromagnetically. We show that the π⁰-η and (K⁰D⁺-K⁺D⁰) mixings act constructively to generate strong widths of the order of 140 keV. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order . We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays to obtain a satisfactory description of the available data.

The PANDA detector will allow to investigate the charmonium region in annihilation processes at a energy range for which production cross sections of charmonium states are unknown, in particular for those above the threshold. Cross sections for these states are expected to be rather small, so that it has to be verified that PANDA can cope with small rates. Therefore, several reaction channels have been identified as "benchmark channels" and the PANDA performance has been investigated in Monte Carlo studies. The focus of the charmed benchmark channels is to show the physics performance of the planned apparatus and to investigate the feasibility of separating the physics signal from a huge hadronic background.

The physics program of the PANDA experiment at FAIR, studying antiproton-proton and antiproton-nucleus collisions, is described. A brief overview of the full program is given, but the emphasis is laid on spectroscopy of hidden and open charm mesons, as well as of multi-strange baryons. In addition the investigation of the J/ψ-nucleon interaction using transparency measurements in antiproton-nucleus collisions is discussed.

We employ QCD sum rules to calculate the J/ψ form factors and coupling constants with charmed mesons, by studying three-point correlation functions. In particular, we consider the J/ψD*D and J/ψDD vertices. We determine the momentum dependence of the form factors for kinematical conditions where J/ψ, D or D* are off-shell. Extrapolating to the pole of each of the form factors obtained, we determine the coupling constants. For both couplings, our results (within the errors) are compatible with estimates based on the constituent quark model.

We review dynamical and thermal models for the collectivity and the suppression pattern of charmed mesons — produced in proton–nucleus and nucleus–nucleus collisions at SPS (~158 A GeV) and RHIC energies (~21 A TeV). In particular, we examine the charmonium "melting" and the "comover dissociation" scenarios — implemented in a microscopic transport approach — in comparison to the available data from the SPS and RHIC. The analysis shows that the dynamics of c and quarks. quarks at RHIC are dominated by partonic or "pre-hadronic" interactions in the strongly coupled plasma stage and can neither be modeled by "hadronic" interactions nor described appropriately by color screening alone. Both the "charmonium melting" and the hadronic "comover absorption and recreation model" are found, however, to be compatible with the experimental observation at SPS energies; the experimental ratio of Ψ′/J/Ψ versus centrality clearly favors the "hadronic comover" scenario. We find that the collective flow of charm in the purely hadronic Hadron-String Dynamics (HSD) transport appears compatible with the data at SPS energies, but the data at top RHIC energies are substantially underestimated. Thus, the large elliptic flow v₂ of D-mesons and the low R_AA(p_T) of J/Ψ seen experimentally have to be attributed to early interactions of non-hadronic degrees of freedom. Simultaneously, we observe that non-hadronic interactions are mandatory in order to describe the narrowing of the J/Ψ rapidity distribution from pp to central Au + Au collisions at the top RHIC energy of . Additionally we demonstrate that the strong quenching of high-p_TJ/Ψ's in central Au + Au collisions indicates that a large fraction of final J/Ψ mesons is created by a coalescence mechanism close to the phase boundary. Throughout this review we, furthermore, provide predictions for charm observables from Au + Au collisions at FAIR energies of 25–35 A GeV.

We review how quark models are able to describe the phenomenology of the charm meson sector. The spectroscopy and decays of charmonium and open charm mesons are described in a particular quark model and compared with the data and the results of other existing models in the literature. A quite reasonable global description of the heavy meson spectra is reached. A new assignment of the ψ(4415) resonance as a 3D state leaving aside the 4S state to the X(4360) is tested through the analysis of the resonance structure in e⁺e^- exclusive reactions around the ψ(4415) energy region. We make tentative assignments of some of the XYZ mesons. To elucidate the structure of the 1⁺cs states, i.e., D_s1(2460) and D_s1(2536), we study the strong decay properties of the D_s1(2536) meson. We also perform a calculation of the branching fractions for the semileptonic decays of B and B_s mesons into final states containing orbitally excited charmed and charmed-strange mesons, which have become a very important source of information about the structure of heavy mesons. Analysis of the nonleptonic B-meson decays into D^(*)D_sJ are also included.

The properties of charmed mesons in nuclear matter and nuclei are reviewed. Different frameworks are discussed paying a special attention to unitarized coupled-channel approaches which incorporate heavy-quark spin symmetry. Several charmed baryon states with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with 1/2⁺ and 3/2⁺ baryons. These states are compared to experimental data. Moreover, the properties of open-charm mesons in matter are analyzed. The in-medium solution accounts for Pauli blocking effects, and for the meson self-energies in a self-consistent manner. The behavior in the nuclear medium of the rich spectrum of dynamically-generated baryon states is studied as well as their influence in the self-energy and, hence, the spectral function of open charm. The possible experimental signatures of the in-medium properties of open charm are finally addressed, such as the formation of charmed nuclei, in connection with the future FAIR facility.

The form factor and the coupling constant of the vertex J/ψD_s D_s was calculated using the QCD Sum Rules. We have considered the cases where the J/ψ and D_s mesons are off-shell.

We present a selection of recent charm results from the BESIII Collaboration. The topics include measurements of strong phase in D⁰ → Kπ decay and y_CP, decay constant f_D⁺ measurement from D⁺ → μ⁺ν, form-factors measurement in D⁰ → K⁻e⁺ν, π⁻e⁺ν, Dalitz plot analysis of , search for D⁰ → γγ rare decay and D_s decays.