Total Cross Sections for Negative and Positive Pions in Hydrogen and Deuterium

Abstract

External meson beams, ranging in energy from 135 Mev to 260 Mev for the ${\pi }^{-}$, and 135 Mev to 198 Mev for the ${\pi }^{+}$, have been used for the measurement of total cross sections by an attenuation experiment using liquid hydrogen as well as C${\mathrm{H}}_2$ and C as absorbers. Possible errors introduced by contamination of the ${\pi }^{+}$ beam by protons have been eliminated by use of time-of-flight and pulse-height discrimination. The corrected cross sections for ${\pi }^{-}$ mesons in hydrogen rise from 47 mb at 133 Mev to a maximum of about 66 mb near 180 Mev and fall thereafter to 38 mb at 258 Mev, with typical uncertainties of ±5 percent. The cross sections for ${\pi }^{+}$ mesons rise from 122 mb at 128 Mev to around 200 mb between 170 Mev and 196 Mev, with accuracy comparable to that for the ${\pi }^{-}$ mesons except for the very high energies where the beams are of low intensity. The ${\pi }^{+}$ cross sections follow very well the curve representing three times the total ${\pi }^{-}$ cross section, indicating that in the measured energy range the dominant interaction between pion and nucleon occurs for total isobaric spin $I=\frac{3}{2}$. Comparison of the ${\pi }^{-}$ cross section with $\left(\frac{8}{3}\right)\pi {\lambda }^2$ supports the idea that the particular angular momentum state $J=\frac{3}{2}$, $L=1\mathrm{}$ (for $I=\frac{3}{2}$) is especially prominent in the scattering.