Interplay of quark and meson degrees of freedom in a near-threshold resonance

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.     

Some two body non-leptonicB decays and estimation off D in the heavy quark effective theory

We have studied some of the two body nonleptonic decays ofB meson in the context of heavy quark effective theory using factorization hypothesis. Treatinga ₁ as a free parameter, we have obtained its value asa ₁=0.822±0.045, by correlating the experimental and predicted branching ratio for process. With this value ofa ₁ the branching ratios obtained for other decay channels are in good agreement with the experiment. The decay constant ofD meson is extracted to be 280.82 MeV. Heavy quark spin symmetry has also been tested.     

A P-matrix analysis of nucleon-nucleon scattering below 1 GeV inspired by the quark compound bag model

The quark compound bag model was suggested recently as a dynamical model for the hadronic interaction, taking quark degrees of freedom into account. Important parameters of this model are the positions and residues of the Jaffe-Low P-matrix poles. They can be extracted from the experimental data on the S-matrix. The P-matrix is determined for several nucleon-nucleon channels. A realistic long-range interaction is included in this analysis which introduces a small model dependence in P. The Wigner-Breit condition on the P-matrix can be used to detect deficiencies of existing phase-shift analyses at low energies.     

Quark potential in a quark–meson plasma

We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T _c≤3, with T _c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.     

Near threshold effects in positron-atom (molecule) scattering

The energy dependence of the total cross-sections for ionization by positron impact has been measured for He, Ne, Ar, CO₂ and O₂. The interplay between this and other scattering channels has been investigated. The data for He, Ne and Ar has been interpreted using a combination ofR-matrix and threshold theories in the neighbourhood of the Ps formation threshold. In CO₂, an enhancement of the Ps formation probability is found when the remnant ion is left in an excited state. In O₂, structure has been observed which indicates channel-coupling with excitation to the Schumann-Runge continuum.     

K-matrix analysis of the (IJ<Superscript>PC</Superscript> = 00<Superscript>+ +</Superscript>)-wave in the mass region below 1900 MeV

We present the results of the current analysis of the partial wave IJ ^PC = 00^{+ +} based on the available data for meson spectra ( ππ, KˉK,ηη,η,ππππ). In the framework of the K-matrix approach, the analytical amplitude has been reconstructed in the mass region 280 MeV < < 1900 MeV. The following scalar-isoscalar states are seen: comparatively narrow resonances f ₀(980), f ₀(1300), f ₀(1500), f ₀(1750) and the broad state f₀(1200-1600). The positions of the amplitude poles (masses and total widths of the resonances) are determined as well as pole residues (partial widths to meson channels ππ, KˉK,ηη,η,ππππ). The fitted amplitude gives us the positions of the K-matrix poles (bare states) and the values of bare-state couplings to meson channels thus allowing the quark-antiquark nonet classification of bare states. On the basis of the obtained partial widths to the channels ππ, KˉK,ηη,η, we estimate the quark/gluonium content of f ₀(980), f ₀(1300), f ₀(1500), f ₀(1750), f₀(1200-1600). For f ₀(980), f ₀(1300), f ₀(1500) and f ₀(1750), their partial widths testify the qˉq origin of these mesons though being unable to provide precise evaluation of the possible admixture of the gluonium component in these resonances. The ratios of the decay coupling constants for the f₀(1200-1600) support the idea about the gluonium nature of this broad state. Received: 14 May 2002 / Accepted: 20 August 2002 / Published online: 11 February 2003 RID="a" ID="a"e-mail: anisovic@thd.pnpi.spb.ru Communicated by A. Sch?fer     

Determination of heavy-meson wave functions from B decays

We extract the B, D, and meson wave functions from the CLEO data of the decays and in the perturbative QCD framework. In this formalism, various logarithmic corrections are organized to give the Wilson evolution from the W boson mass down to the characteristic scale of a decay process, which is of order of the b quark mass, and the Sudakov evolution from the characteristic scale to a lower factorization scale of order . With large logarithms organized, the b quark decay amplitudes are evaluated reliably in perturbation theory. Below the factorization scale, QCD dynamics is regarded as being nonperturbative, and absorbed into meson wave functions. Because of their universality, the heavy-meson wave functions determined in this work, can be employed to make predictions of other decay modes. We also observe that the dependence of heavy meson wave functions on intrinsic parton transverse momenta plays an important role in the explanation of data. Received: 18 February 1999 / Revised version: 24 June 1999 / Published online: 3 November 1999     

DsJ (2317) meson production at RHIC

We study the production of D _sJ (2317) mesons in relativistic heavy ion collisions using the quark coalescence model. The predicted D _sJ (2317) abundance depends sensitively on the quark structure of the D _sJ (2317) meson. We have also evaluated the absorption cross sections of the D _sJ (2317) meson by π, ρ, kaon and K* in a phenomenological hadronic model. We find that the final yield of D _sJ (2317) mesons remains sensitive to its initial number produced from the quark-gluon plasma, providing thus the possibility of studying the quark structure of the D _sJ (2317) meson and its production mechanism in relativistic heavy ion collisions.     

Leptonic constant of the pseudoscalar <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> meson

We calculate the leptonic constant for the pseudoscalar ground state of the B _c meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy quark current in nonrelativistic QCD as matched with full QCD.     

Meson loops in the f0(980) and a0(980) radiative decays into ρ , ω

We calculate the radiative decay widths of the a ₀(980) and f ₀(980) scalar mesons into ργ and ωγ considering the dynamically generated nature of these scalar resonances within the realm of the chiral unitary approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two-meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.     

Effective meson lagrangian with chiral and heavy quark symmetries from quark flavor dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)_F symmetry breaking effects are estimated and, if possible, confronted with experiment.     

Chiral unitary theory: Application to nuclear problems

In this talk we briefly describe some basic elements of chiral perturbation theory, xPT, and how the implementation of unitarity and other novel elements lead to a better expansion of the T-matrix for meson-meson and meson-baryon interactions. Applications are then done to the ππ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and K ⁻ atoms, and how the φ meson properties are changed in a nuclear medium.     

Scalar mesons and multichannel amplitudes

Properties of scalar–isoscalar mesons are analyzed in a unitary model using separable interactions in three decay channels: $\pi\pi, and an effective . We obtain different solutions by fitting various data on the and phase shifts and inelasticities including the CERN–Cracow–Munich measurements of the reaction on a polarized target. The analytical structure of the meson–meson multichannel amplitudes is studied with special emphasis on the role played by the S-matrix zeroes. S-matrix poles, located in the complex energy plane not too far from the physical region, are interpreted as scalar resonances. We see a wide , a narrow and a relatively narrow . In one of our solutions a resonance at about 1700 MeV is also found. Total, elastic and inelastic channel cross sections, branching ratios and coupling constants are evaluated and compared with available data. We construct an approximation to our model and show that the Breit–Wigner approach has a limited phenomenological applicability. Received: 19 October 1998 / Revised version: 25 January 1999 / Published online: 15 April 1999     

Recombination model for hadron production

We calculate baryon distributions in the fragmentation region ofpp collision using Das and Hwa picture of quark recombination. A new estimation of the sea quark distributions in proton is obtained by fitting the pseudoscalar meson data at fixedP _T taking account of parton transverse momenta.     

Unified QCD determination of all pseudoscalar leptonic decay constants

Leptonic decay constants of all pseudoscalar mesons are determined in QCD by means of a new QCD sum-rule method. In the light meson and heavy quark limit the results are very similar and also agree with the well-known PCAC and scaling predictions respectively. The corrections to light meson pole dominance are generally small while those to the heavy quark limit are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainf =132 MeV,f _k=161 MeV,f _B=128±28 MeV,f _D=175±13 MeV,f _Bs=144±30 MeV andf _Ds=193±12 MeV.Work supported by Bundesministerium für Forschung und Technologie (BMFT) under contract No. 06MZ758     

Study of semileptonic and nonleptonic decays of the B<Subscript>c</Subscript><Superscript>-</Superscript> meson

We evaluate semileptonic and two-meson nonleptonic decays of the B _c ^- meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one-body current operators at the quark level. Our model reproduces the constraints of heavy-quark spin symmetry obtained in the limit of infinite heavy-quark mass. For the two-meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.     

Parton distributions from lattice QCD

We extract the x dependence of the valence nonsinglet u - d distribution function in the nucleon from the lowest few moments calculated on the lattice, using an extrapolation formula which ensures the correct behavior in the chiral and heavy quark limits. We discuss the implications for the quark mass dependence of meson masses lying on the J^PC = 1^{– -} Regge trajectory.