An explanation of the ABC enhancement in the dd -> alpha X reaction at intermediate energies

The dd -> alpha X reaction is studied in a model where each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reaction. The condition that the two deuterons fuse to form an alpha-particle then leads to peaks at small missing masses, the well-known ABC enhancement, but also a broad structure around the maximum missing mass. With a simplified input amplitude the model gives a quantitative description of both the alpha-particle momentum and angular distributions for a deuteron beam energy of 1250 MeV.