Near-threshold production of a0(980) mesons in the reaction pp -> d K^+ \bar{K}^0

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 -> d K \bar{K} as well as the background of non-resonant K\bar{K}-pair production. We argue that the reaction pp -> d K^+ \bar{K}^0 at an energy release Q<=100 MeV is dominated by the intermediate production of the a0(980)-resonance. At larger energies the non-resonant K^+\bar{K}^0-pair production - where the kaons are produced in a relative P-wave - becomes important. Then 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-J\"ulich for Q<=107 MeV the a_0^+ signal can reliably be separated from the non-resonant K^+\bar{K^0} background.Comment: 14 pages, 12 figures, submitted to EPJ

Photon induced Lambda(1520) production and the role of the K^* exchange

We study the photon induced Lambda(1520) production in the effective Lagrangian method near threshold, E_\gamma^{LAB}<2 GeV, and in the quark-gluon string model at higher energies 3 GeV < E_\gamma^{LAB} < 5 GeV. In particular, we study the role of the K^* exchange for the production of Lambda(1520) within the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74 (2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^* pair, which is dynamically generated, turns out to be relatively small and, thus, the K exchange mechanism dominates the reaction. In the higher energy region, where experimental data are available, the quark-gluon string mechanism with the K Regge trajectory reproduces both the energy and the angular distribution dependences of the Lambda(1520) photo-production reaction.Comment: 20 pages and 6 page

a0(980)-f0(980) mixing and isospin violation in the reactions pN -> d a0, pd -> 3He/3H a0 and dd -> 4He a0

It is demonstrated that f_0-a_0 mixing can lead to a comparatively large isospin violation in the reactions pN -> da_0, pd -> ^3He/^3H a_0 and dd -> ^4He a_0 close to the corresponding production thresholds. The observation of such mixing effects is possible, e.g., by measuring the forward-backward asymmetry in the reaction pn -> d a_0^0 -> d eta pi^0.Comment: 14 pages, 5 figure

K^- ^3He and K^+K^- interactions in the pd -> ^3He K^+K^- reaction

We investigate the K^- ^3He and K^+ K^- interactions in the reaction pd -> ^3He K^+ K^- near threshold and compare our model calculations with data from the MOMO experiment at COSY-Juelich. A large attractive effective K^- p amplitude would give a significant K^- ^3He final-state interaction effect which is not supported by the experimental data. We also estimate upper limits for the a_0(980) and f_0(980) contributions to the produced K^+ K^- pairs.Comment: 5 pages, 2 figures, accepted for publication in PR

Production of a0a_0-mesons in the reactions πN→a0N\pi N \to a_0 N and pp→da0+p p \to d a_0^+ at GeV energies

We investigate the reactions $\pi N \to a_0 N$ and $p p \to d a_0^+$ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross section of the reaction $\pi N \to a_0 N$. These results are used to calculate the differential and total cross sections of the reaction $p p \to d a_0^+$ within the framework of the two-step model in which two nucleons produce an $a_0$-meson via $\pi$ -meson exchange and fuse to a deuteron. The necessity of new measurements on $a_0$ production and branching fractions (of its decay to the $K\bar K$ and $\pi\eta$ channels) is emphasized for clarifying the $a_0$ structure. Detailed predictions for the reaction $pp \to d a_0^+$ are presented for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure

Omega- and phi-meson production in p n -> d M reactions near threshold and OZI-rule violation

We investigate the reactions p n -> d omega and p n -> d phi close to the corresponding thresholds. The S-wave amplitudes are calculated within the framework of the two-step model which is described by a triangle graph with pi, rho and omega mesons in the intermediate state. The cross sections of the reactions p n -> d omega and p n -> d phi are predicted to be significantly larger than the cross sections of the corresponding reactions p p -> p p omega and p p -> p p phi at the same values of the c.m. excess energy Q. The ratio of the yields of phi to omega is found to be (30 +/- 7) x 10^-3

Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories

We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and square-root form which have been suggested recently by Brisudov\'{a}, Burakovsky and Goldman. We find that the recent experimental data from TJNAF in the few GeV region can reasonably be described by the model. Angular distributions at different $\gamma$-energies are presented and the effect of a forward-backward asymmetry is discussed. Predictions for the energy dependence of $d\sigma/dt$ at higher energies and different $\Theta_{cm}$ are presented, too.Comment: 21 pages, LaTeX, including 6 postscript figures; submitted to Phys. Rev.

Polarization observables in high-energy deuteron photodisintegration within the Quark-Gluon Strings Model

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different $\gamma$-energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5 -- 6 GeV are presented and compared with the available data.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200