Charmed Mesons in Nuclei with Heavy-Quark Spin Symmetry

We study the properties of charmed pseudoscalar and vector mesons in dense matter within a unitary meson–baryon coupled-channel model which incorporates heavy-quark spin symmetry. This is accomplished by extending the SU(3) Weinberg–Tomozawa Lagrangian to incorporate spin-flavor symmetry and implement a suitable flavor symmetry breaking. Several resonances with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with 1/2⁺ and 3/2⁺ baryons. Those states are then compared to experimental data as well as theoretical models. Next, Pauli-blocking effects and meson self-energies are introduced in a self-consistent manner to obtain the open-charm meson spectral functions in a dense nuclear environment. We finally discuss the formation of D-mesic nuclei.     

Charmed hadrons in nuclear medium

We study the properties of charmed hadrons in dense matter within a coupled-channel approach which accounts for Pauli blocking effects and meson self-energies in a self-consistent manner.We analyze the behaviour in this dense environment of dynamically-generated baryonic resonances as well as the open-charm meson spectral functions.We discuss the implications of the in-medium properties of open-charm mesons on the D s0 （2317） and the predicted X（3700） scalar resonances.     

Near-threshold η production in pp collisions

We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances,and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced,and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements.Besides, the invariant mass spectra of pp and pη explain the data well at excess energy of 15 Me V, and are basically consistent with the data at excess energy of 40 Me V. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 Me V, which suggests that a more complicated mechanism is needed at higher energy region.     

Exotic pentaquarks as Gamov-Teller resonances

If the number of colors N c is taken large,baryons and their excitations can be considered in a mean-field approach.We argue that the mean field in baryons breaks spontaneously the spherical and SU(3) flavor symmetries,but retains the SU(2) symmetry of simultaneous rotations in space and isospace.The one-quark and quark-hole excitations in the mean field,together with the SU(3) rotational bands about them determine the spectrum of baryon resonances,which turns out to be in good accordance with reality when one puts N c =3.A by-product of this scheme is a confirmation of the light pentaquark Θ + baryon uudds as a typical Gamov–Teller resonance long known in nuclear physics.An extension of the same large-N c logic to charmed baryons leads to a prediction of a anti-decapenta (15)-plet of charmed pentaquarks,two of which,B ++ c = cuuds and B + c = cudds,may be light and stable with respect to strong decays.     

Charmed baryon resonances with heavy-quark symmetry

We study charmed baryon resonances that are generated dynamically from a coupled-channel unitary approach that implements heavy-quark symmetry. Some states can already be identified with exper-imental observations, such as Λ_c(2595), Λ_c(2660), Σ_c(2902) or Λ_c(2941), while others need a compilation of more experimental data as well as an extension of the model to include higher order contributions. We also compare our model to previous SU(4) schemes.     

Test of duality in baryon-antibaryon amplitudes from Reggeon-particle scattering

By studying the backward production data for meson resonances we investigate the dual properties of baryon-Reggeised antibaryon elastic scattering. We find strong support for the duality prediction that meson resonances in the baryon antibaryon channel should be dual to an exotic trajectory.     

Hadron resonances as rovibrational states

A rovibrational model,including anharmonic,centrifugal,and Coriolis corrections,is used to calculate π,K,N, and Σ orbital and radial resonances.The four orbital excitations of the π meson correspond to the b(1235),π_2(1670),b_3(2030),and π_4(2250) resonances.Its first four radial excitations correspond to the π(1300),π(1800),π(2070),and π(2360) resonances.The orbital excitations of the K meson are interpreted as the K_1(1270),K_2(1770),K_3(2320),and K_4(2500) resonances;its radial excitations correspond to the K(1460) and K(1830) resonances.The N orbital excitations are identified with the N(1520),N(1680),N(2190),N(2220),and N(2600) resonances.The first four radial excitations of the N family correspond to the N(1440),N(1880),N(2100),and N(2300) resonances.The orbital excitations of the Σ baryon are associated with the Σ(1670),Σ(1915),Σ(2100),and Σ(2250) resonances,whereas its radial excitations are identified with the Σ(1660),Σ(1770),and Σ(1880) resonances.The proposed rovibrational model calculations show a good agreement with the corresponding experimental values and allow for the prediction of hadron resonances,thereby proving to be useful for the interpretation of excited hadron spectra.     

T-matrix approach to heavy quark diffusion in the QGP

We assess transport properties of heavy quarks in the quark–gluon plasma (QGP) using static heavy-quark (HQ) potentials from lattice-QCD calculations in a Brueckner many-body T-matrix approach to evaluate elastic heavy-quark–light-quark scattering amplitudes. In the attractive meson and diquark channels, resonance states are formed for temperatures up to ∼1.5T _c, increasing pertinent drag and diffusion coefficients for heavy-quark rescattering in the QGP beyond the expectations from perturbative-QCD calculations. We use these transport coefficients, complemented with perturbative elastic HQ gluon scattering, in a relativistic Langevin simulation to obtain HQ p _t distributions and elliptic flow (v ₂) under conditions relevant for the hot and dense medium created in ultrarelativistic heavy-ion collisions. The heavy quarks are hadronized to open-charm and -bottom mesons within a combined quark-coalescence fragmentation scheme. The resulting single-electron spectra from their semileptonic decays are confronted with recent data on “non-photonic electrons” in 200 A GeV Au–Au collisions at the Relativistic Heavy-Ion Collider (RHIC).     

η-production on the proton via electromagnetic and hadronic probes

The reactions π~-p→ηn and γp→ηp are investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and ρN. The direct η-photoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU(6) O(3) symmetry. In the models search, the following known nucleon resonances are embodied: S_(11)(1535), S_(11)(1650), P_(11)(1440), P_(11)(1710), P_(13)(1720), D_(13)(1520), D_(13)(1700), D_(15)(1675), and F_(15)(1680). Data for the π~-p→ηn reaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P_(13)(1900) and F_(15)(2000), are also considered. However, reproducing the data for γp→ηp requires, within our approach, two new nucleon resonances, for which we extract mass and width.     

Too many X’s, Y’s and Z’s?

Heavy meson spectroscopy above open flavor thresholds has become a challenge both from the experimental and theoretical points of view. Experimentally, several signals have been interpreted as meson resonances with unusual properties; theoretically, such signals may be identified with meson-meson molecules or compact multiquark structures. We analyze the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge multiquark structures as meson-meson molecules.     

Analytic properties of the scattering amplitude and resonances parameters in a meson exchange model

The analytic properties of scattering amplitudes provide important information. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions. In the present study, we determine the pole structure of pion–nucleon scattering in an analytic model based on meson exchange. For this, the sheet structure of the amplitude is determined. To show the precision of the resonance extraction and discuss phenomena such as resonance interference, we discuss the S₁₁ amplitude in greater detail.     

Strangeness production in proton—proton and proton—nucleus collisions

We discuss the investigation of the strange meson production in proton-proton (pp) and proton-nucleus (pA) reactions within an effective Lagrangian model. The kaon production proceeds mainly via excitations ofN*(1650),N*(1710), andN* (1720) resonant intermediate nucleonic states, in the collision of two initial state nucleons. Therefore, the strangeness production is expected to provide information about the resonances lying at higher excitation energies. For beam energies very close to the kaon production threshold the hyperon-proton final state interaction effects are quite important. Thus, these studies provide a check on the models of hyperon-nucleon interactions. The inmedium production of kaons shows strong sensitivity to the self-energies of the intermediate mesons     

The puzzle of the D and D<Subscript>s</Subscript> mesons

We present a theoretical framework that accounts for the new D_J and D_sJ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional P-wave quark-antiquark states and four-quark components. The narrowest states are basically P-wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.     

Partial-wave decomposition of pion and photoproduction amplitudes

Partial-wave amplitudes for production and decay of baryon resonances are constructed in the framework of the operator expansion method. The approach is fully relativistically invariant and allows us to perform combined analyses of different reactions imposing directly analyticity and unitarity constraints. All formulas are given explicitly in the form used by the Crystal Barrel Collaboration in the (partly forthcoming) analyses of the electro-, photo- and pion-induced meson production data.     

The non-ordinary Regge behavior of the $$K^*_0(800)$$ or $$\kappa $$κ-meson versus the ordinary $$K^*_0(1430)$$K0∗(1430)

The Regge trajectory of an elastic resonance can be calculated from dispersion theory, instead of fitted phenomenologically, using only its pole parameters as input. This also provides a correct treatment of resonance widths in Regge trajectories, essential for very wide resonances. In this work we first calculate the \(K^*_0(1430)\) Regge trajectory, finding the ordinary almost real and linear behavior, typical of \(q \bar{q}\) resonances. In contrast, for the \(K^*_0(800)\) meson, the resulting Regge trajectory is non-linear and has a much smaller slope than ordinary resonances, being remarkably similar to that of the \(f_0(500)\) or \(\sigma \) meson. The slope of these unusual Regge trajectories seems to scale with the meson masses rather than with scales typical of quark degrees of freedom. We also calculate the range of the interaction responsible for the formation of these resonances. Our results strongly support a non-ordinary, predominantly meson–meson-like, interpretation for the lightest strange and non-strange resonances.     

Effects of intrasubband coupling on the scattering phases and density of states in a quantum wire

The properties of scattering phases and density of states in a quantum wire with an attractive scatterer are analyzed. We consider two bound states which couple to a scattering channel and give rise to two Fano resonances. It is shown that varying the parameters of the scatterer (such as its strength and position) produces significantly different effects on the phase behavior and density of states, depending on the subband they occur. These effects stem mainly from the difference between the coupling matrix elements of the two resonant levels with the propagating channel mode.