Effects of the nuclear binding of nucleons on pion spectra

Using a magnetic spectrometer a comparative study was made of the energy spectra of π+ and π− -mesons produced in free pp-collisions as well as in pp- and pn-collisions in deutrons and in carbon nuclei at 654 MeV. The forms of the spectra of pions from deuterium and carbon are found to differ due to: a) a larger extent of correlation of nucleons in carbon nuclei than in deuterons; b) differences in the momentum distributions of nucleons in these nuclei; c) secondary pion-nucleon interactions in carbon nuclei. At ≈ 90° in the centre-of-mass system of two colliding nucleons the ratio of the differential cross sections for the production of π+-mesons on free protons and on protons in deuterons and in carbon nuclei was found to be equal to d σ d ω [ p + p →π + ] H : d σ d ω [ p + p →π + ] D : d σ d ω [ p + p →π + ] C = 1:0.79:0.40 , whereas the yields of π− -mesons per neutron for deuterium and carbon were found to be equal. The measured ratio (dσ+/dω)/(dσ−/dω) of the differential cross sections for the production of positive and negative pions on deuterium and carbon is equal to 10.3±1.3 and 6.0±0.8, respectively. The decrease of the value of this ratio for carbon is caused by a considerable contribution of the secondary exchange interaction π0+ n → π−+p to the yield of π− -mesons.