Proton-proton correlation function for the pp -> pp + eta and pp -> pp + pions reactions

For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. The shape of the two-proton correlation function derived for the pp -> ppeta reaction differs from that for the pp -> pp(pions) and both do not show a peak structure opposite to results determined for inclusive measurements of heavy ion collisions.

Upper limit of the total cross section for the pn --> pn eta reaction

The upper limit of the total cross section for the pn --> pn eta reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R_eta = sigma(pn --> pn eta) / sigma(pp --> pp eta) with the corresponding ratio for eta-meson production does not favor the dominance of the N*(1535) resonance in the production process of the eta meson and suggests nonidentical production mechanisms for eta and eta mesons.

Two-proton correlation function for the pp -> pp+eta and pp -> pp+pions reactions

For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. A two-proton correlation function was derived from the data for the pp -> ppX reaction, measured near the threshold of eta meson production. A technique developed for the purpose of this analysis permitted to establish the correlation function separately for the production of the pp+eta and of the pp+pions systems. The shape of the two-proton correlation function for the ppeta differs from that for the pp(pions) and both do not show a peak structure opposite to results determined for inclusive measurements of heavy ion collisions.

Measurement of the invariant mass distributions for the pp -> ppeta reaction at excess energy of Q = 16.4 MeV

The proton-proton and proton-eta invariant mass distributions have been determined for the pp -> ppeta reaction at an excess energy of Q = 16.4 MeV. The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp -> ppeta reaction and reveal an enhancement for large relative proton-proton momenta. This result, together with the fact that the proton-eta interaction is much stronger that the proton-eta interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.

Comparative studies of the interaction in the low energy ppeta and ppeta systems

The COSY-11 collaboration measured the pp -> ppeta and pp -> ppeta reactions in order to perform comparative studies of the interactions within the proton-proton-meson system. This thesis presents in detail the analysis of the pp -> ppeta reaction which was measured at the proton beam momentum of 3.260 GeV/c. The elaboration results in differential distributions of squared invariant proton-proton (s_pp) and proton-eta (s_peta) masses, as well as in angular distributions and the total cross section at an excess energy of 16.4 MeV. The differential distributions s_pp and s_peta are compared to theoretical predictions and to the analogous spectra determined for the pp -> ppeta reaction. The comparison of the results for the eta and eta meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the meson-proton interaction. Further, the shapes of the distributions do not favour any of the postulated theoretical models.

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.

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.

Experimental proton-proton correlation function derived for the pp -> ppeta reaction

Based on the high statistics data from the pp -> ppX reaction measured by the COSY-11 collaboration [1] we have derived a two-proton correlation function for the production of the ppeta and pp+pions systems. The measured correlation function normalized to the value simulated for a point-like source was compared with a theoretical prediction in order to estimate the size of the reaction volume.