Experimental results on the inelastic pion-nucleon interactions at 7 GeV and the formation of isobaric states

Abstract

In a stack of NIKFI-R emulsions, which was irradiated with negative pions at the J.I.N.R. (Dubna), we identified with appropriate criteria 215 π --nucleon interactions. In a careful investigation of the proton momentum distribution the existence of two maxima was established. The corresponding distribution of the inelasticities of the pion-nucleon collisions shows also two maxima with the mean values K = 0.30 and K ≈ 0.68 . Remarkable differences are shown in the momentum and angular distributions of the secondary particles in the two groups of interactions with K ≦ 0.5 and K > 0.5. The experimental data agree with the assumption that the collisions of K ≦ 0.5 could have proceeded via the formation of isobaric states of the pion and of the nucleon. The cross sections for these reactions are ⪅ 11mb for π −-proton collisions and ⪅ 10 mb for π −-neutron collisions. We established especially the existence of a pronounced peak at M π∗ ≈ 765 MeV in the π ∗ mass spectrum for π −- nucleon interactions with K ≦ 0.5.