As simple as ABC - the dd → α X reaction explained

Abstract: A model is presented for the dd → αππ reaction. It is based on two parallell and almost independent NN → dπ processes, where the final deutrons fuse to form the α particle. While underestimating the results at lower energies, the modelgives a good quantitative description of the α-particle momentum distributions throughout the 0.8 < Td < 1.9 GeV energy range. In particular it reproduces the remarkable peak structure (the ABC effect) that dominates the spectra at these energies. The predictions of deuteron vector and tensor analyzing powers are also in good agreement with data, both in frequency and magnitude of the oscillations.By considering two np → dππ processes instead of NN → dπ, the model is extended to four-pion production. With a simple parameterization of the np → dππ amplitude, the high missing mass part of the dd → αX spectra at Td1.9 GeV could be fairly well reproduced.The model is also applied to dd → αγγ, using two np → dγ processes. This reaction is important as background to the charge-symmetry-breaking reaction dd → απ0. The calculated two-photon contribution is of the same magnitude as a reported π0 signal, taking the experimental resolution into account. New experiments are needed in order to clarify the situation.