Invariant mass distributions for the pp to p p eta reaction at Q=10 MeV

Proton-proton and proton-eta invariant mass distributions and the total cross section for the pp to pp eta reaction have been determined near the threshold at an excess energy of Q=10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q=15.5 MeV and Q= 40MeV.

Comparative Studies of Low Energy ppeta and ppeta-prime Systems with Cosy-11 Detector

We present a comparison of the two-body invariant mass distributions for the pp -> ppeta and pp -> ppeta-prime reactions, both measured at a nominal excess energy value of Q = 15.5 MeV. For the pp -> ppeta reaction, in addition, the differential cross sections were extracted for an excess energy of Q = 10 MeV. The comparison of the results for the eta and eta-prime meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the interaction of the meson and the proton.

Near threshold production of the eta meson via the quasi-free pn --> pn eta reaction

Total cross sections for the quasi-free pn --> pn eta reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding cross sections for the pp --> pp eta reaction by a factor of about three in contrast to the factor of six established for higher excess energies. To large extent, the observed decrease of the ratio sigma(pn --> pn eta)/sigma(pp --> pp eta) towards threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final state interactions. The experiment has been conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton-neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn --> pn eta reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.

Near threshold production of the pseudoscalar mesons at the COSY-11 facility

We summarise measurements of the COSY-11 collaboration concerning the excitation functions of the near threshold pseudoscalar meson production in the proton-proton interaction. The results are discussed in the context of the meson-nucleon and hyperon-nucleon interactions. We conclude that the $eta$-proton interaction is significantly stronger than the eta-proton interaction. Similarly, we found that the hyperon Lambda interacts with the nucleon considerably stronger than the hyperon Sigma, and that the interaction of (K-)-proton is much stronger than this of the (K+)-proton.

Dynamics of the near threshold eta meson production in proton-proton interaction

We present the results of measurements of the analysing power for the p(pol)p --> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret these results within the framework of the meson exchange models. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in s-wave.

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.

Summary of studies of the eta meson production with polarized proton beam at COSY-11

We report on the COSY-11 measurements of the analysing power for the p(pol)p --> ppeta reaction and interpret the results in the framework of the meson exchange models.