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 ir~, and 135 Mev to 198 Mev for the 7r + , have been used for the measurement of total cross sections by an attenuation experiment using liquid hydrogen as well as CH2 and C as absorbers. Possible errors introduced by contamination of the ir + beam by protons have been eliminated by use of time-of-flight and pulse-height discrimination. The corrected cross sections for iT 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 ir + 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 ir~ mesons except for the very high energies where the beams are of low intensity. The ir + cross sections follow very well the curve representing three times the total ir~ cross section, indicating that in the measured energy range the dominant interaction between pion and nucleon occurs for total isobaric spin 7=f. Comparison of the ir~ cross section with (8/3)7rX 2 supports the idea that the particular angular momentum state /= §, L-1 (for /= f) is especially prominent in the scattering.The total cross sections for TT + and if~ mesons interacting with deuterium have also been measured by comparing the transmissions of D 2 0 and H2O cells. Within the accuracy, the TT + and x~ total cross sections are equal, consistent with the principle of charge symmetry. The total scattering cross section of deuterium is less than but of the same order of magnitude as the sum of the hydrogen cross sections for TT + and ir~. DEFLECTING MAGNET SCALE IN FEETFIG.

π−−DScattering at 142 MeV

“…The total interaction cross section becomes o-tot&i^ <TE+I+^neutral = 183=1=7 mb. This is to be compared with the interpolated result cr to tai= 175±8 mb of Ashkin et al 22 and 158±8 mb measured by Ignatenko et al 2Z…”

Pion Production in Pion-Nucleon Collisions

“…The same restriction was encountered previously in the treatment of the isobar model for nucleon-nucleon collisions. 3 However, the assumption of complete separation is probably better satisfied than for the nucleon-nucleon case at comparable energies, because of the large energy of the recoil pion. Thus the recoil pion tends to move a greater distance during the decay time (^10~2 3 sec) than the unexcited nucleon (or the second isobar N*) in the nucleon-nucleon collision.…”

“…This situation is analogous to the corresponding one for nucleon-nucleon collisions. 3 The factor G x in Eq. (1) then depends upon #(##*)> and similarly C also becomes a function of the angle 6 T of the recoil pion.…”

“…The various mass values will be called mi,j (.7=1, 2, • • •)• For each mi t j f the following quantity gj, 1 was evaluated: <x{mi, 3 …”

“…The treatment of the isobar excitation process in pionnucleon collisions was developed in analogy to our previously published isobaric nucleon model 3 for single pion production in nucleon-nucleon collisions with the recoil (unexcited) nucleon being replaced by the recoil pion.…”