Neutron-proton interactions in the energy range (290 ÷ 970) MeV

Abstract

A study of inelastic n-p interactions has been made using the Birmingham 1 GeV synchrotron and a 9 in. diameter liquid hydrogen bubble chamber. 1840 three-pronged events initiated by neutrons in the energy range (290 ÷ 970) MeV have been analysed, the possible reactions being: n + p → p + p + π−; n + p → n + p + π0, π0 → e+ + e- + γ, and n + p → n + p + π+ + π−. The ratio found for the integrated cross-sections σ(n + p → n + p + π0) /σ (n + p → p + p + ρ-) = 2.67 ± 0.43 is shown to resolve a long-standing conflict with charge independence. The energy-dependence of the n + p → p + p + π− cross-section has been inferred from the expected shape of the incident neutron spectrum with the aid of earlier cross-section measurements in the energy range. The laboratory kinetic energy distributions and centre-of-mass angular distributions for protons from ppπ- events suggest that the peripheral mechanism of interaction is important at lower energies and to a greater extent than indicated by the one-pion-exchange model. However the Treiman-Yang test for this model is satisfied for events involving small momentum transfer and (3, 3) isobar production. The cross-section for the reaction n + p → n + p + π+ + π- increases more quickly above threshold than required by the statistical model of Cerulus and Hagedorn, and much more so than required by one-pion-exchange processes. Comparison with p-p scattering results, in which double-pion production is far smaller, emphasizes the importance of theT=0 channel.