Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π^?p → 2π^?π⁺p, π^?p → 2π^?π⁺π^op and π^?p → 2π^?2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π^?p → 2π^?π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π^?p → (2π^?π⁺)p, and of the proton, π^?p → π^?(π^?π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π^?p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π^?p → π^?(π^?π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π^?p → π^?(π^?2π⁺)n. Another strong maximum corresponds to the pion dissociation π^?p → (2π^?π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π^?p → (2π^?2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π^?p → (2π^?π⁺)(π^op) and π^?p → (2π^?π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.