Leptonic decays of the eta meson with the WASA detector at CELSIUS

Decay channels of the eta meson with at least one lepton pair in the final state are discussed. Preliminary results on electron-positron pair production from the pd->He eta reaction from the WASA experiment at CELSIUS are presented.Comment: 8 pages, 7 figures, prepared for Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Cracow, 17-22 June 200

Two-proton correlation function: a gentle introduction

The recent COSY-11 collaboration measurement of the two-proton correlation function in the pp -> ppeta reaction, reported at this meeting [1], arouse some interest in a simple theoretical description of the correlation function. In these notes we present a pedagogical introduction to the practical methods that can be used for calculating the correlation function.Comment: Prepared for the proceedings of the Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Krakow, Poland, 17-22 June 200

η′\eta' production in proton-proton collisions far from the threshold

I discuss exclusive production of the $\eta'$ meson in the $pp \to p\eta'p$ reaction far from the threshold. The contribution of diffractive component as well as that for $\gamma^* \gamma^* \to \eta'$ fusion are calculated. In the first case the formalism of unintegrated gluon distribution functions (UGDF) is used. The distributions in the Feynman $x_F$ (or rapidity), transferred four-momenta squared between initial and final protons ($t_1$, $t_2$) and azimuthal angle difference between outgoing protons ($\Phi$) are calculated. The deviations from the $\sin^2(\Phi)$ dependence predicted by one-step vector-vector-pseudoscalar coupling are quantified and discussed. The results are compared with the results of the WA102 collaboration at CERN. Most of the models of UGDF from the literature give too small cross section as compared to the WA102 data and predict angular distribution in relative azimuthal angle strongly asymmetric with respect to $\pi/2$ in disagreement with the WA102 data. This points to a different mechanism at the WA102 energy. Predictions for RHIC, Tevatron and LHC are given.Comment: 7 pages, 6 figures and 1 table invited talk at the symposium on meson physics at COSY11 and WASA-at-COSY, Cracow, Poland, June 17-22, 200

COSY-11 : How will we remember it ?

A personal selection is made of the highlights of the COSY-11 physics program undertaken at the COoler SYnchrotron of the Forschungszentrum Juelich. This has been particularly rich in the field of strange and non-strange meson production in proton-proton and proton-deuteron collisions. The results are considered in relation to experiments carried out at other facilities and with respect to their impact on theory.Comment: Invited talk at the "Symposium on Meson Physics at COSY--11", Cracow, June 2007. 14 pages + 12 eps figures. AIP conference styl

Physics of EtaPrime->Pi+Pi-Eta and EtaPrime->Pi+Pi-Pi0 decays

The article describes experimental status of EtaPrime->Pi+Pi-Eta and EtaPrime->Pi+Pi-Pi0 decays. A theoretical framework used for description of the decays mechanism is also reviewed. The possibilities for the measurements with WASA-at-COSY are mentioned.Comment: Proceedings from Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Cracow, 17-22 June 200

Summary of the COSY-11 Measurements of Hyperon Production

The studies of hyperon production performed at COSY-11 are summarized. The results of the experiments in the reaction channels pp-->pK+Lambda, pp-->pK+Sigma0, and pp-->nK+Sigma+ are shown. Excitation functions fromthreshold up to about 90MeV excess energies have been evaluated with high precision for the Lambda and Sigma0 production. The Lambdap and Sigma0p final state interactions were extracted. The Sigma+ production was measured at 13 and 60 MeV excess energies.Comment: 8 pages, 4 figures, Talk given at Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Cracow, Poland, 17-22 Jun 200

Model-independent approach to eta -> pi+ pi- gamma and eta' -> pi+ pi- gamma

We present a new, model-independent method to analyze radiative decays of mesons to a vector, isovector pair of pions of invariant mass square below the first significant pion-pion threshold in the vector channel. It is based on a combination of chiral perturbation theory and dispersion theory. This allows for a controlled inclusion of resonance physics without the necessity to involve vector meson dominance explicitly. As an example, the method is applied to an analysis of the reactions eta -> pi+ pi- gamma and eta'->pi+ pi- gamma.Comment: 16 pages, 4 figure

Luminosity determination for the quasi-free nuclear reactions

A method for the calculation of the luminosity for the proton-nucleus collisions based on the quasi-free proton-proton scattering is presented. As an example of application the integrated luminosity for the scattering of protons off the deuteron target is determined for the experiment of the quasi-free pn --> pneta reaction performed by means of the COSY-11 facility.Comment: 7 pages, 5 figures, Presented at Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Cracow, Poland, 17-22 Jun 200