Susana Coito

Delicate interplay between the D0-D*0, rho0-J/psi, and omega-J/psi channels in the X(3872) resonance

The nature of the X(3872) enhancement is analyzed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular JPC=1++ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo–Zweig–Iizuka-forbidden ρ0J/ψ and ωJ/ψ channels are coupled as well, but effectively smeared out by using complex ρ0 and ω masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the D0D∗0, ρ0J/ψ, and ωJ/ψ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector

Multichannel calculation of excited vector {phi} resonances and the {phi}(2170)

c\bar{c}

Delicate interplay between the D 0 D ∗0, ρ 0 J/ψ, and ωJ/ψ channels in the X(3872) resonance

resonance, with a pole at or slightly below the D0D∗0 threshold.

Quasi-bound states in the continuum: a dynamical coupled-channel calculation of axial-vector charmed mesons

A multichannel calculation of excited J{sup PC}=1{sup --}{phi} states is carried out within a generalization of the resonance-spectrum expansion, which may shed light on the classification of the {phi}(2170) resonance, discovered by BABAR and originally denoted X(2175). In this framework, a complete spectrum of bare ss states is coupled to those Okubo-Zweig-Iizuka-allowed decay channels that should be most relevant for the considered energy range. The included S- and P-wave two-meson channels comprise the lowest pseudoscalar, vector, scalar, and axial-vector mesons, while in the qq sector both the {sup 3}S{sub 1} and {sup 3}D{sub 1} states are coupled. The only two free parameters are tuned so as to reproduce mass and width of the {phi}(1020), but come out reasonably close to previously used values. Among the models T-matrix poles, there are good candidates for observed resonances, as well as other ones that should exist according to the quark model. Besides the expected resonances as unitarized confinement states, a dynamical resonance pole is found at (2186-i246) MeV. The huge width makes its interpretation as the {phi}(2170) somewhat dubious, but further improvements of the model may change this conclusion.

No Serious Meson Spectroscopy Without Scattering

The nature of the X(3872) enhancement is analyzed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular JPC=1++ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo–Zweig–Iizuka-forbidden ρ0J/ψ and ωJ/ψ channels are coupled as well, but effectively smeared out by using complex ρ0 and ω masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the D0D∗0, ρ0J/ψ, and ωJ/ψ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector

Modeling Two-boson Mass Distributions,

c\bar{c}

E

resonance, with a pole at or slightly below the D0D∗0 threshold.

(38 MeV) and

Masses and widths of the charmed axial-vector mesons D1(2420), D1(2430), Ds1(2536), and Ds1(2460) are calculated nonperturbatively in the Resonance-Spectrum-Expansion model, by coupling various open and closed meson-meson channels to the bare J P = 1 + c n (n = u;d) and c s states. The coupling to two-meson channels dynamically mixes and lifts the mass degeneracy of the spectroscopic 3 P1 and 1 P1 states, as an alternative to the usual spin-orbit splitting. Of the two resulting S-matrix poles in either case, one stays very close to the energy of the bare state, as a quasi-bound state in the continuum, whereas the other shifts considerably. This is in agreement with the experimental observation that the D1(2420) and Ds1(2536) have much smaller widths than one would naively expect. The whole pattern of masses and widths of the axial-vector charmed mesons can thus be quite well reproduced with only two free parameters, one of which being already strongly constrained by previous model calculations.

Z

The principal purpose of meson spectroscopy is to understand the confining force, which is generally assumed to be based on low-energy QCD. This is usually done in the context of quark models that ignore the dynamical effects of quark-pair creation and decay. Very recent lattice calculations confirm much earlier model results showing that neglecting such effects, in the so-called quenched approximation, may give rise to discrepancies of hundreds of MeV, and so distort the meson spectra resulting from quark confinement only. Models attempting to mimic unquenching through a redefinition of the constituent quark mass or screening of the confining potential at larger interquark separations are clearly incapable of accounting for the highly non-perturbative and non-linear effects on mesonic bound-state and resonance poles, as demonstrated with several published examples.

(57.5 GeV)

Besides general features of two-boson mass distributions, experimental results are are discussed. Furthermore, E(38 MeV) and Z(57.5 GeV) are highlighted.