  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.

Nuclear Experiment;Nuclear Theory