Fast Meson Interactions in Nuclear Emulsions. II.π+Mesons

Abstract

${\ensuremath{\pi}}^{+}$ mesons produced in the exterior proton beam of the Berkeley cyclotron are bent by an auxiliary magnet and detected in Ilford G5 emulsions. These mesons are studied in the same way as were the ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons in Part I of this experiment. Extra care is taken to eliminate protons from the data and a special technique is developed to make more efficient small angle scattering measurements. The average initial energy, 45.5 Mev, is slightly higher than that of the ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons, and the spread in energy is greater. Less than 18 percent of observed track is less than 30 Mev and 98 percent of it is over 22 Mev.No disappearances are found over the 902 cm of track. Fewer are expected than were found in Part I, since the average number of charged prongs is greater for ${\ensuremath{\pi}}^{+}$ induced stars than for ${\ensuremath{\pi}}^{\ensuremath{-}}$. No inelastic scatters are found among the 5 scatters greater than 30\ifmmode^\circ\else\textdegree\fi{}. Though the star frequency is the same as in the previous experiment, the frequency for scatters is significantly lower, a fact which is not explained by the slightly higher energy. A statistical upper bound on the cross section for ${\ensuremath{\pi}}^{+}$ scattering on hydrogen is obtained as 2.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}26}$ ${\mathrm{cm}}^{2}$.