Production of Chargedπ-Mesons in H, D, C, Cu, and Pb by 381-Mev Protons

Abstract

The differential cross section for the production of charged $\pi$-mesons at 90° from a 381-Mev proton beam has been measured in H, D, C, Cu, and Pb. Nuclear emulsions, imbedded in a tapered copper absorber, placed 90° below the internal circulating proton beam of the Nevis cyclotron detected mesons of both signs, from 0 to 125 Mev. The beam was monitored by means of the ${\mathrm{C}}^{11}$ activity produced in the target to determine the absolute cross section. The hydrogen and deuterium results were obtained by subtracting the carbon cross section from polyethylene and deuterated paraffin, respectively. Assuming the reaction in H is $p+p\to {\pi }^{+}+d$ with a ${cos}^2\theta$ angular distribution, the total cross section for H at 381 Mev is calculated from the 90° value to be (7.3±2.3)×${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$. The spectra for heavy nuclei are calculated with the assumptions that meson production occurs through nucleon-nucleon collisions and that the meson receives the maximum available energy in the c.m. system. Good agreement with the experimental results is found for matrix elements proportional to meson momentum. The ${\pi }^{+}$ production cross section increases with a dependence slower than $A^{\frac{2}{3}}$, whereas the ${\pi }^{-}$ increases approximately as $A^{\frac{2}{3}}$. This asymmetry is also found in the large $\frac{{\pi }^{+}}{{\pi }^{-}}$ ratio of 10 in carbon and about 25 in deuterium.