Search

The effect of quark-gluon vertex dressing on the ground-state masses of theu/d-quark pseudoscalar, vector and axialvector mesons is considered with the Dyson-Schwinger equations. This extends the ladder-rainbow Bethe-Salpeter kernel to two-loops. To render the calculations feasible for this exploratory study, we employ a simple infrared dominant model for the gluon exchange that implements the vertex dressing. The resulting model, involving two distinct representations of the effective gluon exchange kernel, preserves both the axial-vector Ward-Takahashi identity and charge conjugation symmetry. Numerical results confirm that the pseudoscalar meson retains its Goldstone boson character. The vector meson mass, already at a very acceptable value at ladder level, receives only 30?MeV of attraction from this vertex dressing. For the axial-vector states, which are about 300?MeV too low in ladder approximation, the results are mixed: The 1+- state receives 290?MeV of repulsion, but the 1++ state is lowered further by 30?MeV. The exotic channels 0-- and 1-+ are found to have no states below 1.5?GeV in this model. [ABSTRACT FROM AUTHOR]

Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model, we analyze near-threshold production of a0(980)-mesons in the reaction NN → dK &Kmacr; as well as the background of non-resonant K &Kmacr;-pair production. We argue that the reaction pp → dK+ &Kmacr;0 at an energy release Q ≤ 100MeV is dominated by the intermediate production of the a0(980)-resonance. At larger energies the non-resonant K+ &Kmacr;0-pair production — where the kaons are produced in a relative P-wave — becomes important. The effects of final-state interactions are evaluated in a unitarized scattering length approach and found to be in the order of a 20% suppression close to threshold. Thus, in present experiments at the Cooler Synchrotron COSY-Jülich for Q ≤ 107 MeV the a0+ signal can reliably be separated from the non-resonant K+ &Kmacr;00 background. [ABSTRACT FROM AUTHOR]

The production and decay of vector mesons (p, w) in pA and AA reactions is studied with particular emphasis on their in-medium spectral functions. It is explored within transport calculations if hadronic in-medium decays like Π+π- or π°γ might provide complementary information to their dilepton (e+e-) decays. Whereas the π+&pi,- signal from the p-meson is found to be strongly distorted by pion rescattering, the w-meson Dalitz decay to π°γ appears promising even for more heavy nuclei in 7A and pA reactions. Furthermore, the influence of nucleon and kaon/antikaon potentials on the K± yields and spectra in pA collisions is calculated and compared to the recent data from the ANKE Collaboration. [ABSTRACT FROM AUTHOR]

We consider near-threshold a[sub 0](980)-meson production in πN and NN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN reactions are used to calculate the contribution of the a[sub 0] meson to the cross sections and invariant KK mass distributions of the reactions pp → pnK[sup +]K[sup 0] and pp → ppK[sup +]K[sup –]. It is found that the experimental observation of a[sub 0][sup +] mesons in the reaction pp → pnK[sup +]K[sup 0] is much more promising than the observation of a[sub 0][sup 0] mesons in the reaction pp → ppK[sup +]K[sup –]. Effects of isospin violation in the reactions pN → da[sub 0], pd → [sup 3]He([sup 3]H)a[sub 0], and dd → [sup 4]Hea[sub 0], which are induced by a[sub 0](980)–f[sub 0](980) mixing, are also analyzed.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]