Neutral Pion-Deuteron Production in 400-Mevn−pCollisions

The reaction $n+p\to d+{\pi }^0$ has been studied in a high-pressure hydrogen-filled diffusion cloud chamber. A total of 102 deuterons were identified by a technique of ionization measurement in conjunction with momentum measured in the 10 500-gauss magnetic field. From the laboratory deuteron angle and momentum, the pion angle and the incident neutron energy can be deduced with good resolution, provided the pion is emitted backward in the center-of-mass system. Proton recoils were observed simultaneously, from which the incident neutron flux and energy spectrum were determined. The energy spectrum is centered at 400 Mev with a spread of ±25 Mev. From 52 events occurring in the backward direction the angular distribution of pion emission was found to be consistent with (${{0.28}_{-0.14\mathrm{}}}^{+0.26\mathrm{}}+{{cos}^2\overline{\psi }}_{\pi }$), where the limits include 70 percent of the probability and ${\overline{\psi }}_{\pi }$ is the pion angle in the center-of-mass system. The observed excitation function and total cross section determined from 60 events is consistent with $(0.47\mathrm{}\pm 0.08){\eta }^3$ millibran, where $\eta$ is the center-of-mass pion momentum in rest mass units. These results agree, within the accuracy of the measurements, with the prediction of charge independence that the ratio of this reaction to $p+p\to d+{\pi }^{+}$ should be ½.