Production of Eta Mesons in Proton-Proton Collisions Close to Threshold
  A brief experimental overview on the close-to-threshold eta meson production in proton-proton interactions is presented and the available observables in measurements with unpolarized and polarized beam and target are discussed. 
R. Czyzykiewicz, H.-H. Adam, A. Budzanowski, D. Grzonka, M. Janusz, L.   Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja,...