Crossed Channel Isospin Amplitude Analysis of the Reaction pN→Nπ Δ(1236) above 6 GeV/c Incident Momentum

Abstract

Data on the reactions pn → NπΔ(1236) and pp → NπΔ(1236) at 19 GeV/c have been used to study the reactions pN → N(πΔ) and pN → (Nπ)Δ in terms of crossed channel isospin amplitudes. The cross section of the reaction pN → N(πΔ) is about twice that of pN → (Nπ)Δ. Each reaction can be described by three amplitudes MIIx, where Ix and I are the isospins of the exchange and of the Δπ or Nπ system, respectively. We find that for the reaction where the pion clusters to the Δ, i.e., pN → N(πΔ), the isoscalar exchange is the leading mechanism, but the M3/21 amplitude also gives a large contribution. For the other reaction, i.e., pN → (Nπ)Δ, the isovector exchange amplitude leading to a I = 3/2 Nπ state, is dominating. The Ix = 2 exchange amplitude is unimportant. These results have been compared with the results of similar analyses of other three-body reactions and some common features and differences have been pointed out.Available data at other energies have been used to investigate the energy dependence of the isospin amplitudes for the reaction pN → ΔπN in a double exchange representation. It is found that the amplitude involving isoscalar exchange is dominating above 20 GeV/c and has a weak energy dependence while the amplitude with double isovector exchange has an energy dependence pnlab with n ≈ - 1.5.