Reaction<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>+</mml:mo><mml:mi>p</mml:mi><mml:mo>→</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>+</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>+</mml:mo><mml:mi>n</mml:mi></mml:math>from 360 to 800 MeV

Abstract

The reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+n$ is studied in the Lawrence Radiation Laboratory's 72-in. hydrogen bubble chamber. Events are located by scanning the pictures for ${\ensuremath{\pi}}^{+}$ tracks. Cross sections, Dalitz plots, and ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}n$ mass spectra are given at 360-, 430-, 460-, 480-, 555-, 605-, 673-, and 780-MeV beam energies. No clear evidence is found for ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ resonances between threshold and 680 MeV. However, there is a strong preference for high ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ effective masses, especially at the lowest beam energies. Arguments are given to ascrib this anomaly to the $I=0$ state of the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ system. The ${{N}_{\frac{3}{2}}}^{*}(1238)$ isobar is observed in its negative charge state. The angular distribution of its production is discussed.