Study of the ABC Enhancement in the d d -> alpha X reaction
  The polarized d d -> alpha X reaction at beam energies close to the eta threshold shows very strong structure in the missing mass corresponding to the ABC enhancement. The deuteron tensor analysing power A_yy, and the slope of the vector analysing power A_y with respect to angle, have been measured for this reaction around the forward direction. Both signals are small, and their variations with the alpha-particle momentum are in broad agreement with a theoretical model in which each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reaction. 
R. Wurzinger, O. Bing, M. Boivin, P. Courtat, G. Faldt, R.   Gacougnolle, A. Gardestig, F. Hibou, Y. Le Bornec, J.M. Martin,...