arXiv subjects
Publications and source records attributed to Yu. S. Kalashnikova.
We discuss methods and approaches to the description of molecular states in the spectrum of heavy quarks and investigate in detail various properties of the exotic charmonium-like state X(3872) in the framework of the mesonic molecule model.
Data on open-charm channels collected by the Belle Collaboration are analysed simultaneously using a unitary approach based on a coupled-channel model in a wide energy range $\sqrt{s}=3.7÷4.7$ GeV. The resulting fit provides a remarkably good overall description of the line shapes in all studied channels. Parameters of 5 vector charmonium resonances are extracted from the fit.
Various aspects of the Generalised Nambu-Jona-Lasinio model for QCD in four dimensions are reviewed. The properties of mesonic excitations are discussed in detail, with special attention paid to the chiral pion. The spontaneous chiral symmetry breaking in the vacuum and the effective chiral symmetry restoration in the spectrum of highly excited mesons and baryons are described microscopically.
The QCD string model is employed to evaluate the masses of orbitally and radially excited heavy-light mesons and lightest hybrids in the spectrum of charmonium and bottomonium. The number of parameters of the model is reduced to only seven which are the string tension, the two values of the strong coupling constant (one for heavy-light and $\bar{c}c$ mesons and one for $\bar{b}b$ mesons), and the four overall spectrum shift constants which depend on the quark contents of the particular meson or hybrid family. A few well-established states in the spectrum of heavy-light and heavy-heavy mesons are used to fix these parameters, and then the masses of other mesons and hybrids come out as predictions of the model which are confronted with the existing experimental data, and a few suggestions are made concerning yet not measured quantum numbers of some states in the spectrum of charmonium and bottomonium.
We propose a practical parametrisation for the line shapes of near-threshold states compatible with all requirements of unitarity and analyticity. The coupled-channel system underlying the proposed parametrisation includes bare poles and an arbitrary number of elastic and inelastic channels treated fully nonperturbatively. The resulting formulae are general enough to be used for a simultaneous analysis of the data in all available production and decay channels of the (system of) state(s) under consideration for a quite wide class of reactions. As an example, we fit the experimental data currently available for several decay channels for the charged $Z_b^{(\prime)}$ states in the spectrum of bottomonia and find a good overall description of the data. We find the present data to be consistent with the $Z_b(10610)$ as a virtual state and with the $Z_b(10650)$ as a resonance, both residing very close to the $B\bar{B}^*$ and $B^*\bar{B}^*$ threshold, respectively.
Numerous quarkonium(like) states lying near $S$-wave thresholds are observed experimentally. We propose a self-consistent approach to these near-threshold states compatible with unitarity and analyticity. The underlying coupled-channel system includes a bare pole and an arbitrary number of elastic and inelastic channels treated fully nonperturbatively. The resulting analytical parametrization is ideally suited for a combined analysis of the data available in various channels that is exemplified by an excellent overall description of the data for the charged $Z_b(10610)$ and $Z_b(10650)$ states.
Starting from the hypothesis that the X(3872) is a $D\bar D^*$ molecule, we discuss the radiative decays of the X(3872) into $γJ/ψ$ and $γψ'$ from an effective field theory point of view. We show that radiative decays are very weakly sensitive to the long-range structure of the X(3872). In particular, contrary to earlier claims, we argue that the experimentally determined ratio of the mentioned branching fractions is not in conflict with a wave function of the X(3872) that is dominated by the $D\bar D^*$ hadronic molecular component.
We re-examine one-pion exchange as a possible binding mechanism in the X(3872) charmonium-like state and argue it to be not sufficiently binding for this purpose. We conclude therefore that other short-range dynamics are responsible for the X formation.
We re-analyse the two- and three-pion mass distributions in the decays X(3872)->rho J/psi and X(3872)->omega J/psi and argue that the present data favour the 1++ assignment for the quantum numbers of the X.
We investigate the role played by the three-body $D\bar{D}π$ dynamics on the near-threshold resonance X(3872) charmonium state, which is assumed to be formed by nonperturbative $D\bar D^*$ dynamics. It is demonstrated that, as compared to the naive static-pions approximation, the imaginary parts that originate from the inclusion of dynamical pions reduce substantially the width from the $D\bar{D}π$ intermediate state. In particular, for a resonance peaked at 0.5 MeV below the $D^0\bar D^{*0}$ threshold, this contribution to the width is reduced by about a factor of 2, and the effect of the pion dynamics on the width grows as long as the resonance is shifted towards the $D^0\bar{D^0}π^0$ threshold. Although the physical width of the $X$ is dominated by inelastic channels, our finding should still be of importance for the $X$ line shapes in the $D\bar{D}π$ channel below $D{\bar D}^*$ threshold. For example, in the scattering length approximation, the imaginary part of the scattering length includes effects of all the pion dynamics and does not only stem from the $D^*$ width. Meanwhile, we find that another important quantity for the $X$ phenomenology, the residue at the $X$ pole, is weakly sensitive to dynamical pions. In particular, we find that the binding energy dependence of this quantity from the full calculation is close to that found from a model with pointlike $D\bar D^*$ interactions only, consistent with earlier claims. Coupled-channel effects (inclusion of the charged $D\bar{D}^*$ channel) turn out to have a moderate impact on the results.
We investigate the interplay of quark and meson degrees of freedom in a physical state representing a near-threshold resonance for the case of multiple continuum channels. The aim is to demonstrate the full complexity of near-threshold phenomena. It turns out that those are especially rich, if both quark and meson dynamics generate simultaneously weakly coupled near-threshold poles in the S-matrix. We study the properties of this scenario in detail, such as t-matrix and production amplitude zeros, as well as various effects of the continuum channels interplay.
The 1D2 charmonium assignment for the X(3872) meson is considered, as prompted by a recent result from the BABAR Collaboration, favouring 2-+ quantum numbers for the X. It is shown that established properties of the X(3872) are in a drastic conflict with the 1D2 c-anti-c assignment.
We discuss on very general grounds possible lineshapes of composite particles with one unstable constituent. Expressions are derived in a coupled-channel formalism for constituents interacting in an S-wave with no assumption made on the width of one of them. We show how easy-to-use formulae, already existing in the literature, emerge for narrow constituents and identify the parameter that controls the regime of their applicability.
We demonstrate that in calculation, where unitarity constraints are properly imposed, the deeply bound hadronic molecules recently proposed by Close and Downum do not exist.
We investigate the interplay of quark and meson degrees of freedom in a physical state representing a near-threshold resonance for the case of a single continuum channel. We demonstrate that such a near-threshold resonance may possess quite peculiar properties if both quark and meson dynamics generate weakly coupled near-threshold poles in the S-matrix. In particular, the scattering t-matrix may possess zeros in this case. We also discuss possible implications for production reactions as well as studies within lattice QCD.
Properties of the charmonium-like state X(3872) are investigated and its nature is discussed as based on the existing experimental data. In particular, we analyse the new data from Belle and BaBar Collaborations and argue that, while the BaBar data prefer the dynamically generated virtual state in the D\bar{D}* system, the new Belle data clearly indicate a sizable c\bar{c} 2^3P_1 component in the X wave function.
In this manuscript we comment on the criticism raised recently by Achasov and Kiselev [Phys. Rev. D 76, 077501 (2007)] on our work on the radiative decays phi to gamma a_0/f_0 [Eur. Phys. J. A 24, 437 (2005)]. Specifically, we demonstrate that their criticism relies on results that violate gauge-invariance and is therefore invalid.
QCD string model is employed to calculate the masses and spin splittings of lowest charmonium hybrid states with a magnetic gluon. Relative decay rates into various S- and P-wave D-meson pairs are calculated for these hybrids.