On the Question of Charge Symmetry inD-DReactions

Abstract

The question of charge symmetry in D-D reactions is discussed in light of the recently discovered virtual excited states of the alpha particle. We point out their effects on the asymmetries in the angular distributions as well as the provision of a mechanism for P-wave enhancement. Relation with three-nucleon isobars is also discussed. D+D-+p+H 3 , D+D->n+He 3 (la) (lb) are also of interest from the viewpoints of nuclear structure and of general quantum mechanical symmetry principles. Of the latter, the most obvious fact is that the Bose statistics of the initial T = 0 system requires that there be no interference between the even and odd angular momentum partial waves; and that among the initial singlet, triplet and quintet spin states only the triplet state can couple with the odd partial waves. An immediate consequence of this is that the angular distribution of the reaction products must be symmetric about 90° in the center of mass system. 3 ) Another fact which follows from overall angular momentum and parity conservation (neglecting the small ad­ mixture of weak interaction current) is that the ground states of the three-body nuclei have positive parity. Reaction (la) also provides the most accurate test to-date of the reciprocity theorem in strong interactions. 4 ) These observations do not depend on the reaction mechanism or on what goes on in the intermediate state. In addition, recent measurements 1 ) of reactions (la) and (lb) bave aroused some controversy with regard to the question of charge symmetry in the three­ nucleon isobars. These measurements showed that the zero-to-ninety-degree asymmetry for the angular distribution of the final neutrons is strikingly larger than that of. the protons. One might argue that this difference could arise from the difference in the mass radii of He 3 and H 3 • Such a difference in the cor­