Study of exclusive one-pion and one-eta production using hadron and   dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and   2.2 GeV with HADES
  We present measurements of exclusive \pi^{+,0} and \eta\ production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy in hadron and dielectron channels. In the case of \pi^+ and \pi^0, high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of \Delta(1232) and higher lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross sections are of special interest in the case of pp \to pp \eta, since controversial data exist at 2.0 GeV; we find \sigma =0.142 \pm 0.022 mb. Using the dielectron channels, the \pi^0 and \eta\ Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions. 
HADES Collaboration: G. Agakishiev, H. Alvarez-Pol, A. Balanda, R.   Bassini, M. B\"ohmer, H. Bokemeyer, J. L. Boyard, P. Ca...
nucl-ex