Free and Quasi-free Production of gamma, pi, eta, and eta' bosons in Nucleon-Nucleon Collisions


This letter comprises suggestions for investigations of few different physics issues by means of the measurement of the total and differential cross sections of the production of gamma, pi, eta, and eta' bosons in the collisions of nucleons in various isospin combinations. It is proposed

  1. to make a systematic study of the dependence of the meson production cross sections in nucleon-nucleon collisions as a function of the nucleon virtuality defined as a difference between a mass of a free nucleon and the mass of its virtual counterpart inside eg. a deuteron.
  2. to study thepi andeta meson production in neutron-neutron collisions via double quasi-free nn->nnX reactions. A Dalitz-plot analysis of the n-n-meson system would enable eg. to study the neutron-neutron and neutron-meson scattering lengths, the first is still not well etablished and the second - in case of eta - is only roughly estimated, yet highly desired as one of the key constants in hadron physics. It will also allow to determine the production cross sections in the channel of isospin equal to one without the necessity of correcting for the Coulomb interaction.
  3. to investigate theeta' meson structure and the isospin dependence of its creation in the nucleon-nucleon interaction by comparing its production in proton-proton and proton-neutron collisions. The excitation function for pp->pp eta' is already established. In August 2004 the COSY-11 collaboration will start measurements of the pn->pn eta' reaction in the excess energy range between 0 and 30 MeV and these could be extended up to the excess energy of about 150 MeV when using WASA@COSY.
  4. to search for a signal from the eta-proton and eta'-proton interaction, which should manifest itself as a modification of events population on a Dalitz-plot of a pp->ppX reaction. At present such investigations are carried out at COSY-11, however, due to the need of the subtraction of the unavoidable multi-pion background, the available statistics allows only for the determination of one-dimensional invariant mass distributions, yet the full information of the mutual interaction between ejectiles is excessible from the two-dimensional spectra. The detection of protons and an independent identification of the produced meson via the detection of the gamma quants would allow to determine a background free Dalitz-plot.
  5. to measure the nucleon-nucleon bremsstrahlung radiation. This process is highly sensitive to the nucleon-nucleon potential, and hence may serve as a tool to discriminate between various existing models. Moreover, since the interaction of gamma quants with nucleons is negligibly small in comparison to the meson-nucleon one, a comparative study of the NNeta, NNeta', and NNgamma systems will certainly allow to draw less model dependend conclusions of the Neta and Neta' interaction than those) which might follow from the study of the meson production only.

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