Pion Production by Pions

Abstract

A liquid hydrogen target was bombarded by negative pions of energies 260, 317, 371, and 427 Mev. Positive pions from the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}+n$ were detected by the use of a counter telescope, that selected the ${\ensuremath{\pi}}^{+}$ by its characteristic $\ensuremath{\pi}\ensuremath{-}\ensuremath{\mu}$ decay. With the 260-Mev beam, ${\ensuremath{\pi}}^{+}$ mesons were counted at 90\ifmmode^\circ\else\textdegree\fi{} in the laboratory system. At 317, 371, and 427 Mev, the differential cross section was measured for ${\ensuremath{\pi}}^{+}$ mesons emitted at 60\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 125\ifmmode^\circ\else\textdegree\fi{}, and 160\ifmmode^\circ\else\textdegree\fi{} in the center-of-mass system. The angular distributions are nearly isotropic at 317 and 371 Mev but are peaked forward at 427 Mev. The total cross sections are 0.14\ifmmode\pm\else\textpm\fi{}0.10 mb at 260 Mev, 0.71\ifmmode\pm\else\textpm\fi{}0.17 mb at 317 Mev, 1.93\ifmmode\pm\else\textpm\fi{}0.37 mb at 371 Mev, and 3.36\ifmmode\pm\else\textpm\fi{}0.74 mb at 427 Mev. These results indicate a much larger cross section than the theoretical prediction based on the static model. Reasonable agreement can be obtained by the inclusion of a pion-pion interaction in the production mechanism.