Observations on Neutral $\pi$ Mesons Produced in Nuclear Interactions of 24-Gev Protons with Carbon Nuclei

Energy-angle characteristics of neutral $\pi$ mesons produced in interactions of 24-Gev protons with carbon nuclei have been studied by detecting the $\gamma$ rays from ${\pi }^0$ decay in a small emulsion stack. The energy of the $\gamma$ rays was obtained from the opening angles of electron-positron pairs, using a special measuring criterion which was justified by making multiple scattering measurements on a fraction of the pairs. The average energy of neutral $\pi$ mesons in the c.m. system has been found to be 470±35 Mev. The most probable value of their transverse momentum is 230 Mev/c and the average value is 398±25 Mev/c. It is concluded that at 24 Gev the fraction of the available energy in the c.m. system spent in pion production is 0.43±0.07.